ALBERT

Beschreibung: A sun-tracking method to improve the pointing accuracy of weather radar Atmospheric Measurement Techniques, 5, 547-555, 2012 Author(s): X. Muth, M. Schneebeli, and A. Berne Accurate positioning of data collected by a weather radar is of primary importance for their appropriate georeferencing, which in turn makes it possible to combine those with additional sources of information (topography, land cover maps, meteorological simulations from numerical weather models to list a few). This issue is especially acute for mobile radar systems, for which accurate and stable leveling might be difficult to ensure. The sun is a source of microwave radiation, which can be detected by weather radars and used for accurate positioning of radar data. This paper presents a technique based on the similarity between theodolites and radar systems as well as on the sun echoes to quantify and hence correct the instrumental errors which can affect the pointing accuracy of radar antenna. The proposed method is applied to data collected in the Swiss Alps using a mobile X-band radar system. The obtained instrumental bias values are evaluated by comparing the locations of the ground echoes predicted using these bias estimates with the observed ground echo locations. The very good agreement between the two confirms the accuracy of the proposed method.

Beschreibung: Smoke aerosol and its radiative effects during extreme fire event over Central Russia in summer 2010 Atmospheric Measurement Techniques, 5, 557-568, 2012 Author(s): N. Chubarova, Ye. Nezval', I. Sviridenkov, A. Smirnov, and I. Slutsker Different microphysical, optical and radiative properties of aerosol were analyzed during the severe fires in summer 2010 over Central Russia using ground measurements at two AERONET sites in Moscow (Meteorological Observatory of Moscow State University – MSU MO) and Zvenigorod (Moscow Region) and radiative measurements at the MSU MO. Volume aerosol size distribution in smoke conditions had a bimodal character with the significant prevalence of fine mode particles, for which effective radius was shifted to higher values ( r eff-fine = 0.24 μm against approximately 0.15 μm in typical conditions). For smoke aerosol, the imaginary part of refractive index (REFI) in the visible spectral region was lower than that for typical aerosol (REFI λ =675 nm = 0.006 against REFI λ =675 nm = 0.01), while single scattering albedo (SSA) was significantly higher (SSA λ =675 nm = 0.95 against SSA λ =675 nm ~ 0.9). Extremely high aerosol optical thickness at 500 nm (AOT500) was observed on 6–8 August reaching the absolute maximum on 7 August in Moscow (AOT500 = 6.4) and at Zvenigorod (AOT500 = 5.9). A dramatic attenuation of solar irradiance at ground was also recorded. Maximum irradiance loss had reached 64% for global shortwave irradiance, 91% for UV radiation 300–380 nm, and 97% for erythemally-weighted UV irradiance at relatively high solar elevation 47°. Significant spectral dependence in attenuation of solar irradiance in smoky conditions was mainly explained by higher AOT and smaller SSA in UV (0.8–0.9) compared with SSA in the visible region of spectrum. The assessments of radiative forcing effect (RFE) at the TOA indicated a significant cooling of the smoky atmosphere. Instant RFE reached −167 Wm −2 at AOT500 = 6.4, climatological RFE calculated with August 2010 monthly mean AOT was about −65 Wm −2 , compared with −20 Wm −2 for typical aerosol according to the 10 yr period of measurements in Moscow.

Beschreibung: The relative roles of CO 2 and palaeogeography in determining Late Miocene climate: results from a terrestrial model-data comparison Climate of the Past Discussions, 8, 715-786, 2012 Author(s): C. D. Bradshaw, D. J. Lunt, R. Flecker, U. Salzmann, M. J. Pound, A. M. Haywood, and J. T. Eronen The Late Miocene (∼11.6–5.3 Ma) palaeorecord provides evidence for a warmer and wetter climate than that of today and there is uncertainty in the palaeo-CO 2 record of at least 150 ppmv. We present results from fully coupled atmosphere-ocean-vegetation simulations for the Late Miocene that examine the relative roles of palaeogeography (topography and ice sheet geometry) and CO 2 concentration in the determination of Late Miocene climate through comprehensive terrestrial model-data comparisons. Assuming that the data accurately reflects the Late Miocene climate, and that the Late Miocene palaeogeographic reconstruction used in the model is robust, then results indicate that the proxy-derived precipitation differences between the Late Miocene and modern can be largely accounted for by the palaeogeographic changes alone. However, the proxy-derived temperatures differences between the Late Miocene and modern can only begin to be accounted for if we assume a palaeo-CO 2 concentration towards the higher end of the range of estimates.

Beschreibung: Changes in the strength and width of the Hadley circulation since 1871 Climate of the Past Discussions, 8, 695-713, 2012 Author(s): J. Liu, M. Song, Y. Hu, and X. Ren Recent studies demonstrate that the Hadley Circulation has intensified and expanded for the past three decades, which has important implications for subtropical societies and may lead to profound changes in global climate. However, the robustness of this intensification and expansion that should be considered when interpreting long-term changes of the Hadley Circulation is still matters of debate. It also remains largely unknown how the Hadley Circulation has evolved over longer periods. Here we present long-term variability of the Hadley Circulation using the 20th Century Reanalysis. It shows a slight strengthening and widening of the Hadley Circulation since the late 1970s, which is not inconsistent with recent assessments. However, over centennial timescales (1871–2008), the Hadley Circulation shows a tendency towards more intense and narrower state. More importantly, the width of the Hadley Circulation has not yet completed a life-cycle since 1871. The strength and width of the Hadley Circulation during the late 19th and early 20th century show strong natural variability, exceeding variability that coincides with global warming in recent decades. These findings raise the question that the recent change of the Hadley Circulation is primarily attributed to greenhouse warming or a long-period oscillation of the Hadley Circulation substantially longer than that observed in previous studies.

Beschreibung: Evaluation of Arctic broadband surface radiation measurements Atmospheric Measurement Techniques, 5, 429-438, 2012 Author(s): N. Matsui, C. N. Long, J. Augustine, D. Halliwell, T. Uttal, D. Longenecker, O. Niebergall, J. Wendell, and R. Albee The Arctic is a challenging environment for making in-situ surface radiation measurements. A standard suite of radiation sensors is typically designed to measure incoming and outgoing shortwave (SW) and thermal infrared, or longwave (LW), radiation. Enhancements may include various sensors for measuring irradiance in narrower bandwidths. Many solar radiation/thermal infrared flux sensors utilize protective glass domes and some are mounted on complex mechanical platforms (solar trackers) that keep sensors and shading devices trained on the sun along its diurnal path. High quality measurements require striking a balance between locating stations in a pristine undisturbed setting free of artificial blockage (such as from buildings and towers) and providing accessibility to allow operators to clean and maintain the instruments. Three significant sources of erroneous data in the Arctic include solar tracker malfunctions, rime/frost/snow deposition on the protective glass domes of the radiometers and operational problems due to limited operator access in extreme weather conditions. In this study, comparisons are made between the global and component sum (direct [vertical component] + diffuse) SW measurements. The difference between these two quantities (that theoretically should be zero) is used to illustrate the magnitude and seasonality of arctic radiation flux measurement problems. The problem of rime/frost/snow deposition is investigated in more detail for one case study utilizing both SW and LW measurements. Solutions to these operational problems that utilize measurement redundancy, more sophisticated heating and ventilation strategies and a more systematic program of operational support and subsequent data quality protocols are proposed.

Beschreibung: Millennial-length forward models and pseudoproxies of stalagmite δ 18 O: an example from NW Scotland Climate of the Past Discussions, 8, 869-907, 2012 Author(s): A. Baker, C. Bradley, S. J. Phipps, M. Fischer, I. J. Fairchild, L. Fuller, C. Spötl, and C. Azcurra The stable oxygen isotope parameter δ 18 O remains the most widely utilised speleothem proxy for past climate reconstructions. Uncertainty can be introduced into stalagmite δ 18 O from a number of factors, one of which is the heterogeneity of groundwater flow in karstified aquifers. Here, we present a lumped parameter hydrological model, KarstFor, which is capable of generating monthly simulations of surface water – ground water – stalagmite δ 18 O for more than thousand year time periods. Using a variety of climate input series, we use this model for the first time to compare observational with modelled (pseudoproxy) stalagmite δ 18 O series for a site at Assynt, NW Scotland, where our knowledge of δ 18 O systematics is relatively well understood. The use of forward modelling allows us to quantify the relative contributions of climate, peat and karst hydrology, and disequilibrium effects in stalagmite δ 18 O, from which we can identify potential stalagmite δ 18 O responses to climate variability. Comparison of the modelled and actual stalagmite δ 18 O for two stalagmites from the site demonstrates that for the period of overlapping growth, the two series do not correlate with one another, but forward modelling demonstrates that this falls within the range explicable by differences in flow routing to the stalagmites. Pseudoproxy δ 18 O stalagmite series highlight the potential significance of peat hydrology in controlling stalagmite δ 18 O over the last 1000 years at this site.

Beschreibung: Reconstruction of high resolution atmospheric fields for Northern Europe using analog-upscaling Climate of the Past Discussions, 8, 819-868, 2012 Author(s): F. Schenk and E. Zorita The analog method (AM) has found application to reconstruct gridded climate fields from the information provided by proxy data and climate model simulations. Here, we test the skill of different set-ups of the AM, in a controlled but realistic situation, by analysing several statistical properties of reconstructed daily high-resolution atmospheric fields for Northern Europe for a 50-year period. In this application, station observations of sea-level pressure and air temperature are combined with atmospheric fields from a 50-year high-resolution regional climate simulation. This reconstruction aims at providing homogeneous and physically consistent atmospheric fields with daily resolution suitable to drive high resolution ocean and ecosystem models. Different settings of the AM are evaluated in this study for the period 1958-2007 to estimate the robustness of the reconstruction and its ability to replicate high and low-frequent variability, realistic probability distributions and extremes of different meteorological variables. It is shown that the AM can realistically reconstruct variables with a strong physical link to daily sea-level pressure on daily and monthly scale. However, to reconstruct low-frequency decadal and longer temperature variations, additional monthly mean station temperature as predictor is required. Our results suggest that the AM is a suitable upscaling tool to predict daily fields taken from regional climate simulations based on sparse historical station data. After this testing and characterization of the different set-ups the method will be applied to reconstruct the high-resolution atmospheric fields for the last 160 years.

Beschreibung: Madagascar corals reveal Pacific multidecadal modulation of rainfall since 1708 Climate of the Past Discussions, 8, 787-817, 2012 Author(s): C. A. Grove, J. Zinke, F. Peeters, W. Park, T. Scheufen, S. Kasper, B. Randriamanantsoa, M. T. McCulloch, and G.-J. A. Brummer The Pacific Ocean modulates Australian and North American rainfall variability on multidecadal timescales, in concert with the Pacific Decadal Oscillation (PDO). It has been suggested that Pacific decadal variability may also influence Indian Ocean surface temperature and rainfall in a far-field response, similar to the El Niño Southern Oscillation (ENSO) on interannual timescales. However, instrumental records of rainfall are too short and too sparse to confidently assess such multidecadal climatic teleconnections. Here, we present four climate archives spanning the past 300 yr from giant Madagascar corals. We decouple 20th century human deforestation effects from rainfall induced soil erosion using spectral luminescence scanning and geochemistry. The corals provide the first evidence for Pacific decadal modulation of rainfall over the Western Indian Ocean. We find that positive PDO phases are associated with increased Indian Ocean temperatures and rainfall in Eastern Madagascar, while precipitation in Southern Africa and Eastern Australia declines. Consequently, the negative PDO phase that started in 1998 should lead to reduced rainfall over Eastern Madagascar and increased precipitation in Southern Africa and Eastern Australia. We conclude that the PDO has important implications for future multidecadal variability of African rainfall, where water resource management is increasingly important under the warming climate.

Beschreibung: Profiles of CH 4 , HDO, H 2 O, and N 2 O with improved lower tropospheric vertical resolution from Aura TES radiances Atmospheric Measurement Techniques, 5, 397-411, 2012 Author(s): J. Worden, S. Kulawik, C. Frankenberg, V. Payne, K. Bowman, K. Cady-Peirara, K. Wecht, J.-E. Lee, and D. Noone Thermal infrared (IR) radiances measured near 8 microns contain information about the vertical distribution of water vapor (H 2 O), the water isotopologue HDO, and methane (CH 4 ), key gases in the water and carbon cycles. Previous versions (Version 4 or less) of the TES profile retrieval algorithm used a "spectral-window" approach to minimize uncertainty from interfering species at the expense of reduced vertical resolution and sensitivity. In this manuscript we document changes to the vertical resolution and uncertainties of the TES version 5 retrieval algorithm. In this version (Version 5), joint estimates of H 2 O, HDO, CH 4 and nitrous oxide (N 2 O) are made using radiances from almost the entire spectral region between 1100 cm −1 and 1330 cm −1 . The TES retrieval constraints are also modified in order to better use this information. The new H 2 O estimates show improved vertical resolution in the lower troposphere and boundary layer, while the new HDO/H 2 O estimates can now profile the HDO/H 2 O ratio between 925 hPa and 450 hPa in the tropics and during summertime at high latitudes. The new retrievals are now sensitive to methane in the free troposphere between 800 and 150 mb with peak sensitivity near 500 hPa; whereas in previous versions the sensitivity peaked at 200 hPa. However, the upper troposphere methane concentrations are biased high relative to the lower troposphere by approximately 4% on average. This bias is likely related to temperature, calibration, and/or methane spectroscopy errors. This bias can be mitigated by normalizing the CH 4 estimate by the ratio of the N 2 O estimate relative to the N 2 O prior, under the assumption that the same systematic error affects both the N 2 O and CH 4 estimates. We demonstrate that applying this ratio theoretically reduces the CH 4 estimate for non-retrieved parameters that jointly affect both the N 2 O and CH 4 estimates. The relative upper troposphere to lower troposphere bias is approximately 2.8% after this bias correction. Quality flags based upon the vertical variability of the methane and N 2 O estimates can be used to reduce this bias further. While these new CH 4 , HDO/H 2 O, and H 2 O estimates are consistent with previous TES retrievals in the altitude regions where the sensitivities overlap, future comparisons with independent profile measurement will be required to characterize the biases of these new retrievals and determine if the calculated uncertainties using the new constraints are consistent with actual uncertainties.

Beschreibung: Two instruments based on differential optical absorption spectroscopy (DOAS) to measure accurate ammonia concentrations in the atmosphere Atmospheric Measurement Techniques, 5, 413-427, 2012 Author(s): H. Volten, J. B. Bergwerff, M. Haaima, D. E. Lolkema, A. J. C. Berkhout, G. R. van der Hoff, C. J. M. Potma, R. J. Wichink Kruit, W. A. J. van Pul, and D. P. J. Swart We present two Differential Optical Absorption Spectroscopy (DOAS) instruments built at RIVM: the RIVM DOAS and the miniDOAS. Both instruments provide virtually interference-free measurements of NH 3 concentrations in the atmosphere, since they measure over an open path, without suffering from inlet problems or interference problems by ammonium aerosols dissociating on tubes or filters. They measure concentrations up to at least 200 μg m −3 , have a fast response, low maintenance demands, and a high up-time. The RIVM DOAS has a high accuracy of typically 0.15 μg m −3 for ammonia for 5-min averages and over a total light path of 100 m. The miniDOAS has been developed for application in measurement networks such as the Dutch National Air Quality Monitoring Network (LML). Compared to the RIVM DOAS it has a similar accuracy, but is significantly reduced in size, costs, and handling complexity. The RIVM DOAS and miniDOAS results showed excellent agreement ( R 2 = 0.996) during a field measurement campaign in Vredepeel, the Netherlands. This measurement site is located in an agricultural area and is characterized by highly variable, but on average high ammonia concentrations in the air. The RIVM-DOAS and miniDOAS results were compared to the results of the AMOR instrument, a continuous-flow wet denuder system, which is currently used in the LML. Averaged over longer time spans of typically a day, the (mini)DOAS and AMOR results agree reasonably well, although an offset of the AMOR values compared to the (mini)DOAS results exists. On short time scales, the (mini)DOAS shows a faster response and does not show the memory effects due to inlet tubing and transport of absorption fluids encountered by the AMOR. Due to its high accuracy, high uptime, low maintenance and its open path, the (mini)DOAS shows a good potential for flux measurements by using two (or more) systems in a gradient set-up and applying the aerodynamic gradient technique.

Beschreibung: Detailed insight into Arctic climatic variability during MIS 11 at Lake El'gygytgyn, NE Russia Climate of the Past Discussions, 8, 6309-6339, 2012 Author(s): H. Vogel, C. Meyer-Jacob, M. Melles, J. Brigham-Grette, A. A. Andreev, V. Wennrich, and P. Rosén Here we present a detailed multiproxy record of the climate and environmental evolution at Lake El'gygytgyn/Far East Russian Arctic during the period 430–395 ka covering the Marine Isotope Stage (MIS) 12/11 transition and the thermal maximum of super interglacial MIS 11. The MIS 12/11 transition at Lake El'gygytgyn is characterized by initial warming followed by a cold reversal implying similarities to the Bølling/Allerød (B/A) to Younger Dryas (YD) pattern of the last deglaciation. Full and remarkably stable interglacial conditions with mean temperatures of warmest month (MTWM) ranging between ca. 10–15 °C, annual precipitation (PANN) ranging between ca. 300–600 mm, strong in-lake productivity, coincide with dark coniferous forests in the catchment, annual disintegration of the lake ice cover and full mixis of the water column. Such conditions persisted for ca. 27 kyrs between ca. 425–398 ka. The Lake El'gygytgyn record closely resembles the climate pattern recorded in Lake Baikal (SE Siberia) sediments and Antarctic ice cores implying strong teleconnections between Northern and Southern Hemispheres during MIS 11. A peak warm period between ca. 418–415.5 ka and a precipitation anomaly at ca. 401 ka at Lake El'gygytgyn, in contrast, appear to be an expression of more regionally confined climate variations.

Beschreibung: Technical Note: The single particle soot photometer fails to reliably detect PALAS soot nanoparticles Atmospheric Measurement Techniques, 5, 3099-3107, 2012 Author(s): M. Gysel, M. Laborde, A. A. Mensah, J. C. Corbin, A. Keller, J. Kim, A. Petzold, and B. Sierau The single particle soot photometer (SP2) uses laser-induced incandescence (LII) for the measurement of atmospheric black carbon (BC) particles. The BC mass concentration is obtained by combining quantitative detection of BC mass in single particles with a counting efficiency of 100% above its lower detection limit. It is commonly accepted that a particle must contain at least several tenths of a femtogram BC in order to be detected by the SP2. Here we show the result that most BC particles from a PALAS spark discharge soot generator remain undetected by the SP2, even if their BC mass, as independently determined with an aerosol particle mass analyser (APM), is clearly above the typical lower detection limit of the SP2. Comparison of counting efficiency and effective density data of PALAS soot with flame generated soot (combustion aerosol standard burner, CAST), fullerene soot and carbon black particles (Cabot Regal 400R) reveals that particle morphology can affect the SP2's lower detection limit. PALAS soot particles are fractal-like agglomerates of very small primary particles with a low fractal dimension, resulting in a very low effective density. Such loosely packed particles behave like "the sum of individual primary particles" in the SP2's laser. Accordingly, most PALAS soot particles remain undetected as the SP2's laser intensity is insufficient to heat the primary particles to their vaporisation temperature because of their small size ( D pp ≈ 5–10 nm). Previous knowledge from pulsed laser-induced incandescence indicated that particle morphology might have an effect on the SP2's lower detection limit, however, an increase of the lower detection limit by a factor of ∼5–10, as reported here for PALAS soot, was not expected. In conclusion, the SP2's lower detection limit at a certain laser power depends primarily on the total BC mass per particle for compact particles with sufficiently high effective density. By contrast, the BC mass per primary particle mainly determines whether fractal-like particles with low fractal dimension and very small primary particles are detectable, while their total BC mass has only a minor influence. This effect shifts the lower detection limit to much higher BC mass, or makes them completely undetectable. Consequently, care has to be taken when using the SP2 in applications dealing with loosely packed particles that have very small primary particles as building blocks.

Beschreibung: What controls the spatio-temporal distribution of D-excess and 17 O-excess in precipitation? A general circulation model study Climate of the Past Discussions, 8, 5493-5543, 2012 Author(s): C. Risi, A. Landais, R. Winkler, and F. Vimeux Combined measurements of the H 2 18 O and HDO isotopic ratios in precipitation, leading to second-order parameter D-excess, have provided additional constraints on past climates compared to the H 2 18 O isotopic ratio alone. More recently, measurements of H 2 17 O have led to another second-order parameter: 17 O-excess. Recent studies suggest that 17 O-excess in polar ice may provide information on evaporative conditions at the moisture source. However, the processes controlling the spatio-temporal distribution of 17 O-excess are still far from being fully understood. We use the isotopic general circulation model LMDZ to better understand what controls D-excess and 17 O-excess in precipitation at present-day (PD) and during the last glacial maximum (LGM). The simulation of D-excess and 17 O-excess is evaluated against measurements in meteoric water, water vapor and polar ice cores. A set of sensitivity tests and diagnostics are used to quantify the relative effects of evaporative conditions (sea surface temperature and relative humidity), Rayleigh distillation, precipitation re-evaporation and supersaturation during condensation at low temperature. Simulations suggest that in the tropics convective processes and rain re-evaporation are important controls on D-excess and 17 O-excess. In higher latitudes, the effect of distillation, transport and mixing balance the effect of supersaturation. Since these terms are very large and near cancellation, results for both PD and LGM are very sensitive to the supersaturation function. The lower D-excess and 17 O-excess at LGM simulated at LGM are dominated by the supersaturation effect. Evaporative conditions had previously been suggested to be key controling factors of D-excess and 17 O-excess. In LMDZ, evaporative conditions are key in explaining the PD latitudinal and seasonal distributions, but play little role for 17 O-excess and for LGM variations. However, the LMDZ may underestimate this role. More generally, some shortcomings in the simulation of 17 O-excess by LMDZ suggest that GCMs are not yet the perfect tool to quantify with confidence all processes controlling 17 O-excess.

Beschreibung: Effect of air composition (N 2 , O 2 , Ar, and H 2 O) on CO 2 and CH 4 measurement by wavelength-scanned cavity ring-down spectroscopy: calibration and measurement strategy Atmospheric Measurement Techniques, 5, 2689-2701, 2012 Author(s): H. Nara, H. Tanimoto, Y. Tohjima, H. Mukai, Y. Nojiri, K. Katsumata, and C. W. Rella We examined potential interferences from water vapor and atmospheric background gases (N 2 , O 2 , and Ar), and biases by isotopologues of target species, on accurate measurement of atmospheric CO 2 and CH 4 by means of wavelength-scanned cavity ring-down spectroscopy (WS-CRDS). Changes of the background gas mole fractions in the sample air substantially impacted the CO 2 and CH 4 measurements: variation of CO 2 and CH 4 due to relative increase of each background gas increased as Ar 〈 O 2 〈 N 2 , suggesting similar relation for the pressure-broadening effects (PBEs) among the background gas. The pressure-broadening coefficients due to variations in O 2 and Ar for CO 2 and CH 4 are empirically determined from these experimental results. Calculated PBEs using the pressure-broadening coefficients are linearly correlated with the differences between the mole fractions of O 2 and Ar and their ambient abundances. Although the PBEs calculation showed that impact of natural variation of O 2 is negligible on the CO 2 and CH 4 measurements, significant bias was inferred for the measurement of synthetic standard gases. For gas standards balanced with purified air, the PBEs were estimated to be marginal (up to 0.05 ppm for CO 2 and 0.01 ppb for CH 4 ) although the PBEs were substantial (up to 0.87 ppm for CO 2 and 1.4 ppb for CH 4 ) for standards balanced with synthetic air. For isotopic biases on CO 2 measurements, we compared experimental results and theoretical calculations, which showed excellent agreement within their uncertainty. We derived instrument-specific water correction functions empirically for three WS-CRDS instruments (Picarro EnviroSense 3000i, G-1301, and G-2301), and evaluated the transferability of the water correction function from G-1301 among these instruments. Although the transferability was not proven, no significant difference was found in the water vapor correction function for the investigated WS-CRDS instruments as well as the instruments reported in the past studies within the typical analytical precision at sufficiently low water concentrations (

Beschreibung: Atmospheric effect on the ground-based measurements of broadband surface albedo Atmospheric Measurement Techniques, 5, 2675-2688, 2012 Author(s): T. Manninen, A. Riihelä, and G. de Leeuw Ground-based pyranometer measurements of the (clear-sky) broadband surface albedo are affected by the atmospheric conditions (mainly by aerosol particles, water vapour and ozone). A new semi-empirical method for estimating the magnitude of the effect of atmospheric conditions on surface albedo measurements in clear-sky conditions is presented. Global and reflected radiation and/or aerosol optical depth (AOD) at two wavelengths are needed to apply the method. Depending on the aerosol optical depth and the solar zenith angle values, the effect can be as large as 20%. For the cases we tested using data from the Cabauw atmospheric test site in the Netherlands, the atmosphere caused typically up to 5% overestimation of surface albedo with respect to corresponding black-sky surface albedo values.

Beschreibung: Improved Micro Rain Radar snow measurements using Doppler spectra post-processing Atmospheric Measurement Techniques, 5, 2661-2673, 2012 Author(s): M. Maahn and P. Kollias The Micro Rain Radar 2 (MRR) is a compact Frequency Modulated Continuous Wave (FMCW) system that operates at 24 GHz. The MRR is a low-cost, portable radar system that requires minimum supervision in the field. As such, the MRR is a frequently used radar system for conducting precipitation research. Current MRR drawbacks are the lack of a sophisticated post-processing algorithm to improve its sensitivity (currently at +3 dBz), spurious artefacts concerning radar receiver noise and the lack of high quality Doppler radar moments. Here we propose an improved processing method which is especially suited for snow observations and provides reliable values of effective reflectivity, Doppler velocity and spectral width. The proposed method is freely available on the web and features a noise removal based on recognition of the most significant peak. A dynamic dealiasing routine allows observations even if the Nyquist velocity range is exceeded. Collocated observations over 115 days of a MRR and a pulsed 35.2 GHz MIRA35 cloud radar show a very high agreement for the proposed method for snow, if reflectivities are larger than −5 dBz. The overall sensitivity is increased to −14 and −8 dBz, depending on range. The proposed method exploits the full potential of MRR's hardware and substantially enhances the use of Micro Rain Radar for studies of solid precipitation.

Beschreibung: Comparison of satellite microwave backscattering (ASCAT) and visible/near-infrared reflectances (PARASOL) for the estimation of aeolian aerodynamic roughness length in arid and semi-arid regions Atmospheric Measurement Techniques, 5, 2703-2712, 2012 Author(s): C. Prigent, C. Jiménez, and J. Catherinot Previous studies examined the possibility to estimate the aeolian aerodynamic roughness length from satellites, either from visible/near-infrared observations or from microwave backscattering measurements. Here we compare the potential of the two approaches and propose to merge the two sources of information to benefit from their complementary aspects, i.e. the high spatial resolution of the visible/near-infrared (6 km for PARASOL that is part of the A-Train) and the independence from atmospheric contamination of the active microwaves (ASCAT on board MetOp with a lower spatial resolution of 25 km). A global map of the aeolian aerodynamic roughness length at 6 km resolution is derived, for arid and semi-arid regions. It shows very good consistency with the existing information on the properties of these surfaces. The dataset is available to the community, for use in atmospheric dust transport models.

Beschreibung: Anisotropy of small-scale stratospheric irregularities retrieved from scintillations of a double star α-Cru observed by GOMOS/ENVISAT Atmospheric Measurement Techniques, 5, 2713-2722, 2012 Author(s): V. Kan, V. F. Sofieva, and F. Dalaudier In this paper, we discuss estimating anisotropy of air density irregularities (ratio of characteristic horizontal and vertical scales) from satellite observations of bi-chromatic scintillations of a double star whose components are not resolved by the detector. The analysis is based on fitting experimental auto- and cross-spectra of scintillations by those computed using the 3-D spectral model of atmospheric irregularities consisting of anisotropic and isotropic components. Application of the developed method to the scintillation measurements of the double star α-Cru by GOMOS (Global Ozone Monitoring by Occultation of Stars) fast photometers results in estimates of anisotropy coefficient of ~15–20 at altitudes 30–38 km, as well as other parameters of atmospheric irregularities. The obtained estimates of the anisotropy coefficient correspond to small-scale irregularities, close to the buoyancy scale.

Beschreibung: Development of a new data-processing method for SKYNET sky radiometer observations Atmospheric Measurement Techniques, 5, 2723-2737, 2012 Author(s): M. Hashimoto, T. Nakajima, O. Dubovik, M. Campanelli, H. Che, P. Khatri, T. Takamura, and G. Pandithurai In order to reduce uncertainty in the estimation of Direct Aerosol Radiative Forcing (DARF), it is important to improve the estimation of the single scattering albedo (SSA). In this study, we propose a new data processing method to improve SSA retrievals for the SKYNET sky radiometer network, which is one of the growing number of networks of sun-sky photometers, such as NASA AERONET and others. There are several reports that SSA values from SKYNET have a bias compared to those from AERONET, which is regarded to be the most accurate due to its rigorous calibration routines and data quality and cloud screening algorithms. We investigated possible causes of errors in SSA that might explain the known biases through sensitivity experiments using a numerical model, and also using real data at the SKYNET sites at Pune (18.616° N/73.800° E) in India and Beijing (39.586° N/116.229° E) in China. Sensitivity experiments showed that an uncertainty of the order of ±0.03 in the SSA value can be caused by a possible error in the ground surface albedo or solid view angle assumed for each observation site. Another candidate for possible error in the SSA was found in cirrus contamination generated by imperfect cloud screening in the SKYNET data processing. Therefore, we developed a new data quality control method to get rid of low quality or cloud contamination data, and we applied this method to the real observation data at the Pune site in SKYNET. After applying this method to the observation data, we were able to screen out a large amount of cirrus-contaminated data and to reduce the deviation in the SSA value from that of AERONET. We then estimated DARF using data screened by our new method. The result showed that the method significantly reduced the difference of 5 W m −2 that existed between the SKYNET and AERONET values of DARF before screening. The present study also suggests the necessity of preparing suitable a priori information on the distribution of coarse particles ranging in radius between 10 μm and 30 μm for the analysis of heavily dust-laden atmospheric cases.

Beschreibung: Calibration and intercomparison of acetic acid measurements using proton-transfer-reaction mass spectrometry (PTR-MS) Atmospheric Measurement Techniques, 5, 2739-2750, 2012 Author(s): K. B. Haase, W. C. Keene, A. A. P. Pszenny, H. R. Mayne, R. W. Talbot, and B. C. Sive Acetic acid is one of the most abundant organic acids in the ambient atmosphere, with maximum mixing ratios reaching into the tens of parts per billion by volume (ppbv) range. The identities and associated magnitudes of the major sources and sinks for acetic acid are poorly characterized, due in part to the limitations of available measurement techniques. This paper demonstrates that, when properly calibrated, proton-transfer-reaction mass spectrometry (PTR-MS) can be a valuable technique for fast response, accurate quantification of acetic acid in ambient air. Three different PTR-MS configurations were calibrated at low ppbv mixing ratios using permeation tubes, which yielded calibration factors between 7.0 and 10.9 normalized counts per second per ppbv (ncps ppbv −1 ) at a drift tube field strength of 132 Townsend (Td). Detection limits ranged from 0.06 to 0.32 ppbv with dwell times of 5 s. These calibration factors showed negligible humidity dependence. Acetic acid was measured with PTR-MS on Appledore B Island, ME, during the International Consortium for Atmospheric Research on Transport and Transformation (ICARTT) campaign and validated based on acetic acid measured in parallel using tandem mist chambers coupled with ion chromatography (MC/IC). Mixing ratios ranged from a minimum of 0.075 ± 0.004 ppbv to 3.555 ± 0.171 ppbv, with a median mixing ratio of 0.530 ± 0.025 ppbv. An orthogonal least squares linear regression of paired data yielded a slope of 1.14 ± 0.06 (2σ), an intercept of 0.049 ± 0.020 (2σ) ppbv, and an R 2 of 0.78.

Beschreibung: Airborne observations of formic acid using a chemical ionization mass spectrometer Atmospheric Measurement Techniques, 5, 3029-3039, 2012 Author(s): M. Le Breton, M. R. McGillen, J. B. A. Muller, A. Bacak, D. E. Shallcross, P. Xiao, L. G. Huey, D. Tanner, H. Coe, and C. J. Percival The first airborne measurements of formic acid mixing ratios over the United Kingdom were measured on the FAAM BAe-146 research aircraft on 16 March 2010 with a chemical ionization mass spectrometer using I − reagent ions. The I − ionization scheme was able to measure formic acid mixing ratios at 1 Hz in the boundary layer. In-flight standard addition calibrations from a formic acid source were used to determine the instrument sensitivity of 35 ± 6 ion counts pptv −1 s −1 and a limit of detection of 25 pptv. Routine measurements were made through a scrubbed inlet to determine the instrumental background. Three plumes of formic acid were observed over the UK, originating from London, Humberside and Tyneside. The London plume had the highest formic acid mixing ratio throughout the flight, peaking at 358 pptv. No significant correlations of formic acid with NO x and ozone were found, but a positive correlation was observed between CO and HCOOH within the two plumes where coincident data were recorded. A trajectory model was employed to determine the sources of the plumes and compare modelled mixing ratios with measured values. The model underestimated formic acid concentrations by up to a factor of 2. This is explained by missing sources in the model, which were considered to be both primary emissions of formic acid of mainly anthropogenic origin and a lack of precursor emissions, such as isoprene, from biogenic sources, whose oxidation in situ would lead to formic acid formation.

Beschreibung: Applying spaceborne reflectivity measurements for calculation of the solar ultraviolet radiation at ground level Atmospheric Measurement Techniques, 5, 3041-3054, 2012 Author(s): P. N. den Outer, A. van Dijk, H. Slaper, A. V. Lindfors, H. De Backer, A. F. Bais, U. Feister, T. Koskela, and W. Josefsson Long-term analysis of cloud effects on ultraviolet (UV) radiation on the ground using spaceborne observations requires the use of instruments that have operated consecutively. The longest data record can be built from the reflectivity measurements produced by the instruments Total Ozone Mapping Spectrometers (TOMS) flown on Nimbus 7 from 1979 to 1992, TOMS on Earth Probe from 1996 to 2005, and the Ozone Monitoring Instrument (OMI) flown on EOS Aura since 2004. The reflectivity data produced by TOMS on Earth Probe is only included until 2002. A comparison is made with cloud effects inferred from ground-based pyranometer measurements at over 83 World Radiation Data Centre stations. Modelled UV irradiances utilizing the standard reflectivity are compared with measurements of UV irradiances at eight European low-elevation stations. The reflectivity data of the two TOMS instruments shows a consistent agreement, and the required corrections are of low percentage, i.e. 2–3%. In contrast, the reflectivity product of OMI requires correction of 7–10%, and a solar angle dependency therein is more pronounced. These corrections were inferred from a comparison with pyranometer data, and tested using the UV measurements. The average reduction of UV radiation due to clouds for all sites together indicates a small trend: a diminishing cloudiness, in line with ground-based UV observations. Uncorrected implementation of the reflectivity data would have indicated the opposite. An optimal area was established for reflectivity data for the calculation of daily sums of UV radiation. It measures approximately 1.25° in latitudinal direction for square-shaped areas overhead the ground-based UV stations. Such an area can be traversed within 5 to 7 h at the average wind speeds found for the West European continent.

Beschreibung: Simulating the temperature and precipitation signal in an Alpine ice core Climate of the Past Discussions, 8, 6111-6134, 2012 Author(s): S. Brönnimann, I. Mariani, M. Schwikowski, R. Auchmann, and A. Eichler Accumulation and δ 18 O data from Alpine ice cores provide information on past temperature and precipitation. However, their correlation with seasonal or annual mean temperature and precipitation at nearby sites is often low. Based on an example we argue that, to some extent, this is due to the irregular sampling of the atmosphere by the ice core (i.e. ice cores only record precipitation events and not dry periods) and the possible incongruity between annual layers and calendar year due to dating uncertainty. Using daily meteorological data from nearby stations and reanalyses we replicate the ice core from the Grenzgletscher (Switzerland, 4200 m a.s.l.) on a sample-by-sample basis. Over the last 15 yr of the ice core record, accumulation and δ 18 O variations can be well reproduced on a sub-seasonal scale. This allows a wiggle-matching approach for defining quasi-annual layers. For this period, correlations between measured and replicated quasi-annual δ 18 O values approach 0.8. Further back in time, the quality of the agreement deteriorates rapidly. Nevertheless, we find significant correlations for accumulation and precipitation over the entire length of the record (1938–1993), which is not the case when comparing ice core δ 18 O with annual mean temperature. A Monte Carlo resampling approach of long meteorological time series is used to further explore the relation, in a replicated ice core, between δ 18 O and annual mean temperature. Results show that meteorologically very different years can lead to quasi-identical values for δ 18 O. This poses limitations to the use of δ 18 O from Alpine ice cores for temperature reconstructions in regions with a variable seasonality in precipitation.

Beschreibung: Testing the potential of OSL, TT-OSL, IRSL and post-IR IRSL luminescence dating on a Middle Pleistocene sediment record of Lake El'gygytgyn, Russia Climate of the Past Discussions, 8, 4779-4815, 2012 Author(s): A. Zander and A. Hilgers Lake El'gygytgyn is a 12 km wide crater lake located in remote Chukotka in the far East Russian Arctic about 100 km to the north of the Arctic Circle. It was formed by a meteorite impact about 3.58 Ma ago. This study tests the paleomagnetic and proxy data-based Mid- to Late-Pleistocene sediment deposition history using novel luminescence dating techniques of sediment cores taken from the centre of the 175 m deep lake. For dating polymineral and quartz fine grains (4–11 μm grain size range) were extracted from nine different levels from the upper 28 m of sediment cores 5011-1A and 5011-1B. Polymineral sub-samples were analysed by infra-red stimulated luminescence (IRSL) and post-IR infra-red stimulated luminescence (post-IR IRSL) using single aliquot regenerative dose (SAR) sequences. SAR protocols were further applied to measure the blue light optically stimulated luminescence (OSL) and thermally-transferred OSL (TT-OSL) of fine-grained quartz supplemented by a multiple aliquot TT-OSL approach. According to an independent age model, the lowest sample from 27.8–27.9 m below lake bottom level correlates to the Brunhes-Matuyama (B/M) reversal. Finally, the SAR post-IR-IRSL protocol applied to polymineral fine grains was the only luminescence technique able to provide dating results of acceptable accuracy up to ca. 700 ka. Major factors limiting precision and accuracy of the luminescence chronology are, for some samples, natural signals already approaching saturation level, and overall the uncertainty related to the sediment water content and its variations over geological times.

Beschreibung: Corrigendum to "Greenhouse gas measurements over a 144 km open path in the Canary Islands" published in Atmos. Meas. Tech., 5, 2309–2319, 2012 Atmospheric Measurement Techniques, 5, 2349-2349, 2012 Author(s): J. S. A. Brooke, P. F. Bernath, G. Kirchengast, C. B. Thomas, J.-G. Wang, K. A. Tereszchuk, G. González Abad, R. J. Hargreaves, C. A. Beale, J. J. Harrison, S. Schweitzer, V. Proschek, P. A. Martin, V. L. Kasyutich, C. Gerbig, O. Kolle, and A. Loescher No abstract available.

Beschreibung: NO 2 observations over the western Pacific and Indian Ocean by MAX-DOAS on Kaiyo , a Japanese research vessel Atmospheric Measurement Techniques, 5, 2351-2360, 2012 Author(s): H. Takashima, H. Irie, Y. Kanaya, and F. Syamsudin Nitrogen dioxide (NO 2 ) profile retrievals were performed by ship-borne Multi-Axis Differential Optical Absorption Spectroscopy (MAX-DOAS) using a compact/low-power spectrometer on the Japanese research vessel Kaiyo during two ocean cruises around Japan and Japan–Bali (Indonesia)–Indian Ocean. DOAS analysis using a 425–450 nm fitting window revealed a clear land–ocean contrast in NO 2 differential slant column densities (DSCDs) but poor fitting results and negative values, especially at low elevation angles at low latitudes (

Beschreibung: Estimate of climate sensitivity from carbonate microfossils dated near the Eocene-Oligocene global cooling Climate of the Past Discussions, 8, 4923-4939, 2012 Author(s): M. W. Asten Climate sensitivity is a crucial parameter in global temperature modelling. An estimate is made at the time 33.4 Ma using published high-resolution deep-sea temperature proxy obtained from foraminiferal δ 18 O records from DSDP site 744, combined with published data for atmospheric partial pressure of CO 2 ( p CO 2 ) from carbonate microfossils, where δ 11 B provides a proxy for p CO 2 . The p CO 2 data shows a p CO 2 decrease accompanying the major cooling event of about 4 °C from greenhouse conditions to icecap conditions following the Eocene-Oligocene boundary (33.7 My). During the cooling p CO 2 fell from 1150 to 770 ppmv. The cooling event was followed by a rapid and huge increase in p CO 2 back to 1130 ppmv in the space of 50 000 yr. The large p CO 2 increase was accompanied by a small deep-ocean temperature increase estimated as 0.59 ± 0.063 °C. Climate sensitivity estimated from the latter is 1.1 ± 0.4 °C (66% confidence) compared with the IPCC central value of 3 °C. The post Eocene-Oligocene transition (33.4 Ma) value of 1.1 °C obtained here is lower than those published from Holocene and Pleistocene glaciation-related temperature data (800 Kya to present) but is of similar order to sensitivity estimates published from satellite observations of tropospheric and sea-surface temperature variations. The value of 1.1 °C is grossly different from estimates up to 9 °C published from paleo-temperature studies of Pliocene (3 to 4 Mya) age sediments. The range of apparent climate sensitivity values available from paleo-temperature data suggests that either feedback mechanisms vary widely for the different measurement conditions, or additional factors beyond currently used feedbacks are affecting global temperature-CO 2 relationships.

Beschreibung: Thermomagnetic properties of vivianite nodules, Lake El'gygytgyn, Northeast Russia Climate of the Past Discussions, 8, 4989-5027, 2012 Author(s): P. S. Minyuk, T. V. Subbotnikova, L. L. Brown, and K. J. Murdock Vivianite, a hydrated iron phosphate, is abundant in sediments of El'gygytgyn Lake, located in the Anadyr Mountains of Central Chukotka, Northeastern Russia (67° 30' N; 172° 05' E). Magnetic measurements, including weight low-field AC magnetic susceptibility, field dependent magnetic susceptibility, hysteresis parameters, temperature dependence of the saturation magnetization, as well as susceptibility in different heating media provide ample information on vivianite. Electron-microprobe analyses, electron microscopy and energy dispersive spectroscopy were used to identify diagnostic minerals. Vivianite nodules are abundant in both sediments of cold (anoxic) and warm (oxic) stages. Magnetic susceptibility of the nodules varies from 0.78 × 10 −6 m 3 kg −1 to 1.72 × 10 −6 m 3 kg −1 (average = 1.05 × 10 −6 m 3 kg −1 ) and is higher than the susceptibility of sediments from the cold intervals. Magnetic properties of vivianite are due to product of oxidation as well as sediment and mineral inclusions. Three types of curves of high temperature dependence susceptibility of vivianite indicate different degree of oxidation and inclusions in the nodules. Vivianite acts as a reductant and reduces hematite to magnetite and suppresses the goethite-hematite transition during heating. Heating vivianite and sulfur mixture stimulate the formation of monoclinic pyrrhotite. An additive of arsenic inhibits the formation of magnetite prior to its Curie temperature. Heating selective vivianite and pyrite mixtures produces formation of several different minerals – magnetite, monoclinic pyrrhotite, and hexagonal pyrrhotite, and make it difficult to interpret the thermomagnetic curves.

Beschreibung: Orbital changes, variation in solar activity and increased anthropogenic activities: controls on the Holocene flood frequency in the Lake Ledro area, Northern Italy Climate of the Past Discussions, 8, 4701-4744, 2012 Author(s): B. Vannière, M. Magny, S. Joannin, A. Simonneau, S. B. Wirth, Y. Hamann, E. Chapron, A. Gilli, M. Desmet, and F. S. Anselmetti Two lacustrine sediment cores from Lake Ledro in Northern Italy were studied to produce chronologies of flood events for the past 10 000 yr. For this purpose, we have developed an automatic method that objectively identifies the sedimentary imprint of river floods in the downstream lake basin. The automatic counting of flood deposits was based on colour data extracted from processed core photographs, and the count data were processed to capture the flood signal. Automatic quantification was compared with naked-eye counting. Counts were performed twice on the proximal and distal cores to provide an objective and reproducible record of flood frequency. Geophysical and geochemical analyses made it possible to distinguish event deposits from background sedimentation. Flood frequency and reconstructed sedimentary dynamics were compared with lake-level changes and pollen dynamics inferred from vegetation data. The data suggest a record marked by low flood frequency during the early and middle Holocene (10 000–4500 cal BP). Only modest increases during short intervals are recorded at ca. 8000, 7500, and 7100 cal BP. The last third of the Holocene is characterised by a shift toward increased flood frequency at ca. 4500–4000 cal BP. With the exception of two short intervals around 2900–2500 and 1800–1400 cal BP, which show a slightly reduced number of floods, the trend of increasing flood frequency prevailed until the 20th century, reaching a maximum between the 16th and the 19th centuries. Brief-flood frequency increases recorded during the early and middle Holocene can be attributed to cold climatic oscillations. On a centennial time scale, major changes in flood frequency, such as those observed at ca. 4500 and 500 cal BP, can be attributed to large-scale climatic changes such as the Neo-glacial and Little Ice Age, which are under orbital and possibly solar control. The role of climate as the main forcing factor in flood activity is supported by the lake-level records: the major lake-level rises are synchronous with flood frequency increases. However, in the Bronze Age and during the Middle Ages and modern times, forest clearing and land use are indicated by pollen and archaeological data. These human activities have clearly affected the sediment record of flood activity, and they can partially explain the amplitude of the increases in flood activity.

Beschreibung: Greenhouse gas measurements over a 144 km open path in the Canary Islands Atmospheric Measurement Techniques, 5, 2309-2319, 2012 Author(s): J. S. A. Brooke, P. F. Bernath, G. Kirchengast, C. B. Thomas, J.-G. Wang, K. A. Tereszchuk, G. González Abad, R. J. Hargreaves, C. A. Beale, J. J. Harrison, S. Schweitzer, V. Proschek, P. A. Martin, V. L. Kasyutich, C. Gerbig, O. Kolle, and A. Loescher A new technique for the satellite remote sensing of greenhouse gases in the atmosphere via the absorption of short-wave infrared laser signals transmitted between counter-rotating satellites in low Earth orbit has recently been proposed; this would enable the acquisition of a long-term, stable, global set of altitude-resolved concentration measurements. We present the first ground-based experimental demonstration of this new infrared-laser occultation method, in which the atmospheric absorption of CO 2 near 2.1 μm was measured over a ~144 km path length between two peaks in the Canary Islands (at an altitude of ~2.4 km), using relatively low power diode lasers (~4 to 10 mW). The retrieved CO 2 volume mixing ratio of 400 ppm (±15 ppm) is consistent within experimental uncertainty with simultaneously recorded in situ validation measurements. We conclude that the new method has a sound basis for monitoring CO 2 in the free atmosphere; other greenhouse gases such as methane, nitrous oxide and water vapour can be monitored in the same way.

Beschreibung: An empirical model of optical and radiative characteristics of the tropospheric aerosol over West Siberia in summer Atmospheric Measurement Techniques, 5, 1513-1527, 2012 Author(s): M. V. Panchenko, T. B. Zhuravleva, S. A. Terpugova, V. V. Polkin, and V. S. Kozlov An empirical model of the vertical profiles of aerosol optical characteristics is described. This model was developed based on data acquired from multi-year airborne sensing of optical and microphysical characteristics of the tropospheric aerosol over West Siberia. The main initial characteristics for the creation of the model were measurement data of the vertical profiles of the aerosol angular scattering coefficients in the visible wavelength range, particle size distribution functions and mass concentrations of black carbon (BC). The proposed model allows us to retrieve the aerosol optical and radiative characteristics in the visible and near-IR wavelength range, using the season, air mass type and time of day as input parameters. The columnar single scattering albedo and asymmetry factor of the aerosol scattering phase function, calculated using the average vertical profiles, are in good agreement with data from the AERONET station located in Tomsk. For solar radiative flux calculations, this empirical model has been tested for typical summer conditions. The available experimental database obtained for the regional features of West Siberia and the model developed on this basis are shown to be sufficient for performing these calculations.

Beschreibung: Calibration of an all-sky camera for obtaining sky radiance at three wavelengths Atmospheric Measurement Techniques, 5, 2013-2024, 2012 Author(s): R. Román, M. Antón, A. Cazorla, A. de Miguel, F. J. Olmo, J. Bilbao, and L. Alados-Arboledas This paper proposes a method to obtain spectral sky radiances, at three wavelengths (464, 534 and 626 nm), from hemispherical sky images. Images are registered with the All-Sky Imager installed at the Andalusian Center for Environmental Research (CEAMA) in Granada (Spain). The methodology followed in this work for the absolute calibration in radiance of this instrument is based on the comparison of its output measurements with modelled sky radiances derived from the LibRadtran/UVSPEC radiative transfer code under cloud-free conditions. Previously, in order to check the goodness of the simulated radiances, these are compared with experimental values recorded by a CIMEL sunphotometer. In general, modelled radiances are in agreement with experimental data, showing mean differences lower than 20% except for the pixels located next to the Sun position that show larger errors. The relationship between the output signal of the All-Sky Imager and the modelled sky radiances provides a calibration matrix for each image. The variability of the matrix coefficients is analyzed, showing no significant changes along a period of 5 months. Therefore, a unique calibration matrix per channel is obtained for all selected images (a total of 705 images per channel). Camera radiances are compared with CIMEL radiances, finding mean absolute differences between 2% and 15% except for pixels near to the Sun and high scattering angles. We apply these calibration matrices to three images in order to study the sky radiance distributions for three different sky conditions: cloudless, overcast and partially cloudy. Horizon brightening under cloudless conditions has been observed together with the enhancement effect of individual clouds on sky radiance.

Beschreibung: Modern isotope hydrology and controls on δD of plant leaf waxes at Lake El'gygytgyn, NE Russia Climate of the Past Discussions, 8, 3719-3764, 2012 Author(s): K. M. K. Wilkie, B. Chapligin, H. Meyer, S. Burns, S. Petsch, and J. Brigham-Grette Stable isotope data from lipid biomarkers and diatom silica recovered from lake sediment cores hold great promise for paleoclimate and paleohydrological reconstructions. However, these records rely on accurate calibration with modern precipitation and hydrologic processes. Here we investigate the stable isotopic composition of modern precipitation, streams, lake water and ice cover, and use these data to constrain isotope systematics of the Lake El'gygytgyn basin hydrology. Compound specific hydrogen isotope ratios determined from modern vegetation are compared with modern precipitation and lake core top sediments. Multi-species net (apparent) fractionation values between source water (precipitation) and leaf wax lipids (mean value is −105 ± 13‰) agree with previous results in arid environments and provide a basis for application of this proxy downcore. We conclude that although there may be some bias towards winter precipitation signal, overall leaf wax lipids record annual average precipitation within the El'gygytgyn Basin.

Beschreibung: Aircraft measurements of carbon dioxide and methane for the calibration of ground-based high-resolution Fourier Transform Spectrometers and a comparison to GOSAT data measured over Tsukuba and Moshiri Atmospheric Measurement Techniques, 5, 2003-2012, 2012 Author(s): T. Tanaka, Y. Miyamoto, I. Morino, T. Machida, T. Nagahama, Y. Sawa, H. Matsueda, D. Wunch, S. Kawakami, and O. Uchino Aircraft measurements of carbon dioxide and methane over Tsukuba (36.05° N, 140.12° E) (February 2010) and Moshiri (44.36° N, 142.26° E) (August 2009) were made to calibrate ground-based high-resolution Fourier Transform Spectrometers (g-b FTSs) and to compare with the Greenhouse gases Observing SATellite (GOSAT). The aircraft measurements over Tsukuba in February 2010 were successful in synchronizing with both the g-b FTS and GOSAT for the first time. Airborne in situ and flask-sampling instruments were mounted on the aircraft, and measurements were carried out between altitudes of 0.5 and 7 km to obtain vertical profiles of carbon dioxide (CO 2 ), methane (CH 4 ), and other gaseous species. By comparing the g-b FTS measurements with the airborne measurements, the column-averaged dry air mole fractions of CO 2 (X CO 2 ) and CH 4 (X CH 4 ) retrieved from the g-b FTS measurements at Tsukuba were biased low by 0.33 ± 0.11% for X CO 2 and 0.69 ± 0.29% for X CH 4 . The g-b FTS values at Moshiri were biased low by 1.24% for X CO 2 and 2.11% for X CH 4 . The GOSAT data show biases that are 3.1% ± 1.7% lower for X CO 2 and 2.5% ± 0.8% lower for X CH 4 than the aircraft measurements obtained over Tsukuba.

Beschreibung: Lake El'gygytgyn water and sediment balance components overview and its implications for the sedimentary record Climate of the Past Discussions, 8, 3977-4001, 2012 Author(s): G. Fedorov, M. Nolan, J. Brigham-Grette, D. Bolshiyanov, G. Schwamborn, and O. Juschus Modern process studies of the hydrologic balance and sediment flux into and out of Lake El'gygytgyn, central Chukotka, provide important quantitative estimates for better understanding the lacustrine paleoclimate record from this basin. Formed ca. 3.6 Ma as a result of a meteorite impact, the basin contains one of the longest paleoclimate records in the Arctic. Fluvial activity into the basin today is concentrated over the short snowmelt period. Recent lake-level changes have a slow regressive character due to active underground runoff, even during winter. The residence time of the lake-water is estimated to be about 100 yr. The main source of clastic material are incoming steams. The amount of sediment discharge through the outflow river is insignificant and completely compensated even by little aeolian input.

Beschreibung: Quantitative bias estimates for tropospheric NO 2 columns retrieved from SCIAMACHY, OMI, and GOME-2 using a common standard for East Asia Atmospheric Measurement Techniques, 5, 2403-2411, 2012 Author(s): H. Irie, K. F. Boersma, Y. Kanaya, H. Takashima, X. Pan, and Z. F. Wang For the intercomparison of tropospheric nitrogen dioxide (NO 2 ) vertical column density (VCD) data from three different satellite sensors (SCIAMACHY, OMI, and GOME-2), we use a common standard to quantitatively evaluate the biases for the respective data sets. As the standard, a regression analysis using a single set of collocated ground-based Multi-Axis Differential Optical Absorption Spectroscopy (MAX-DOAS) observations at several sites in Japan and China from 2006–2011 is adopted. Examinations of various spatial coincidence criteria indicates that the slope of the regression line can be influenced by the spatial distribution of NO 2 over the area considered. While the slope varies systematically with the distance between the MAX-DOAS and satellite observation points around Tokyo in Japan, such a systematic dependence is not clearly seen and correlation coefficients are generally higher in comparisons at sites in China. On the basis of these results, we focus mainly on comparisons over China and estimate the biases in SCIAMACHY, OMI, and GOME-2 data (TM4NO2A and DOMINO version 2 products) against the MAX-DOAS observations to be −5 ± 14%, −10 ± 14%, and +1 ± 14%, respectively, which are all small and insignificant. We suggest that these small biases now allow for analyses combining these satellite data for air quality studies, which are more systematic and quantitative than previously possible.

Beschreibung: Stable isotopic evidence of El Niño-like atmospheric circulation in the Pliocene Western United States Climate of the Past Discussions, 8, 5083-5108, 2012 Author(s): M. J. Winnick, J. M. Welker, and C. P. Chamberlain Understanding how the hydrologic cycle has responded to warmer global temperatures in the past is especially important today as concentrations of CO 2 in the atmosphere continue to increase due to human activities. The Pliocene offers an ideal window into a climate system that has equilibrated with current atmospheric p CO 2 . During the Pliocene the Western United States was wetter than modern, an observation at odds with our current understanding of future warming scenarios, which involve the expansion and poleward migration of the subtropical dry zone. Here we compare Pliocene oxygen isotope profiles of pedogenic carbonates across the Western US to modern isotopic anomalies in precipitation between phases of the El Niño Southern Oscillation (ENSO). We find that when accounting for seasonality of carbonate formation, isotopic changes through the late Pliocene match modern precipitation isotopic anomalies in El Niño years. Furthermore, isotopic shifts through the late Pliocene mirror changes through the early Pleistocene, which likely represents the southward migration of the westerly storm track caused by growth of the Laurentide Ice Sheet. We propose that the westerly storm track migrated northward through the late Pliocene with the development of the modern Cold Tongue in the East Equatorial Pacific, then returned southward with widespread glaciation in the Northern Hemisphere – a scenario supported by terrestrial climate proxies across the US. Together these data support the proposed existence of background El Niño-like conditions in Western North America during the warm Pliocene. If the Earth behaves similarly with future warming, this observation has important implications with regard to the amount and distribution of precipitation in Western North America.

Beschreibung: Combined wind measurements by two different lidar instruments in the Arctic middle atmosphere Atmospheric Measurement Techniques, 5, 2433-2445, 2012 Author(s): J. Hildebrand, G. Baumgarten, J. Fiedler, U.-P. Hoppe, B. Kaifler, F.-J. Lübken, and B. P. Williams During a joint campaign in January 2009, the Rayleigh/Mie/Raman (RMR) lidar and the sodium lidar at the ALOMAR Observatory (69° N, 16° E) in Northern Norway were operated simultaneously for more than 40 h, collecting data for wind measurements in the middle atmosphere from 30 up to 110 km altitude. As both lidars share the same receiving telescopes, the upper altitude range of the RMR lidar and the lower altitude range of the sodium lidar overlap in the altitude region of ≈80–85 km. For this overlap region we are thus able to present the first simultaneous wind measurements derived from two different lidar instruments. The comparison of winds derived by RMR and sodium lidar is excellent for long integration times of 10 h as well as shorter ones of 1 h. Combination of data from both lidars allows identifying wavy structures between 30 and 110 km altitude, whose amplitudes increase with height. We have also performed vertical wind measurements and measurements of the same horizontal wind component using two independent lasers and telescopes of the RMR lidar and show how to use this data to calibrate and validate the wind retrieval. For the latter configuration we found a good agreement of the results but also identified inhomogeneities in the horizontal wind at about 55 km altitude of up to 20 ms −1 for an integration time of nearly 4 h. Such small-scale inhomogeneities in the horizontal wind field are an essential challenge when comparing data from different instruments.

Beschreibung: Spatial gradients of temperature, accumulation and δ 18 O-ice in Greenland over a series of Dansgaard-Oeschger events Climate of the Past Discussions, 8, 5209-5261, 2012 Author(s): M. Guillevic, L. Bazin, A. Landais, P. Kindler, A. Orsi, V. Masson-Delmotte, T. Blunier, S. L. Buchardt, E. Capron, M. Leuenberger, P. Martinerie, F. Prié, and B. M. Vinther Air and water stable isotope measurements from three Greenland deep ice cores (GISP2, NGRIP and NEEM) are investigated over a series of Dansgaard-Oeschger events (DO 8-9-10) which are representative of glacial millennial scale variability. Combined with firn modeling, air isotope data allow to quantify abrupt temperature increases for each drill site. Our data show that the magnitude of stadial-interstadial temperature increase is up to 3 °C larger in Central and North Greenland than in North West Greenland. The temporal water isotope (δ 18 O) – temperature relationship varies between 0.3 and 0.6 ± 0.08‰ °C −1 and is systematically larger at NEEM, possibly due to limited changes in precipitation seasonality compared to GISP2 or NGRIP. The gas age-ice age difference of warming events represented in water and air isotopes can only be modeled when assuming a 26% (NGRIP) to 34% (NEEM) lower accumulation than derived from a Dansgaard-Johnsen ice flow model.

Beschreibung: Increasing cloud cover in the 20th century: review and new findings in Spain Climate of the Past Discussions, 8, 1133-1167, 2012 Author(s): A. Sanchez-Lorenzo, J. Calbó, and M. Wild Visual observations of clouds have been performed since the establishment of meteorological observatories during the early instrumental period, and have become more systematic and reliable after the mid-19th century due to the establishment of the first national weather services. During the last decades a large number of studies have documented the trends of the total cloud cover (TCC) and cloudy types; most of these studies are focused on the trends since the second half of the 20th century. Due to the lower reliability of former observations, and the fact that most of this data is not accessible in digital format, there is a lack of studies focusing on the trends of cloudiness since the mid-19th century. In the first part, this work attempts to review the previous studies analyzing TCC changes with information covering at least the first half of the 20th century. Then, the study analyses a database of cloudiness observations in Southern Europe (Spain) since the second third of the 19th century. Specifically, monthly TCC series were reconstructed since 1866 by means of a so-called parameter of cloudiness, calculated from the number of cloudless and overcast days. This estimated TCC series show a high interannual and decadal correlation with the observed TCC series originally measured in oktas. After assessing the temporal homogeneity of the estimated TCC series, the mean annual and seasonal series for the whole of Spain and several subregions were calculated. The mean annual TCC shows a general tendency to increase from the beginning of the series until the 1960s; at this point, the trend becomes negative. The linear trend for the annual mean series, estimated over the 1866–2010 period, is a highly remarkable (and statistically significant) increase of +0.44% per decade, which implies an overall increase of more than +6% during the analyzed period. These results are in line with the major part of the previous trends observed at many areas of the World, especially for the records before the 1950s, when a widespread increase of TCC can been considered as a common feature.

Beschreibung: A 250 ka oxygen isotope record from diatoms at Lake El'gygytgyn, far east Russian Arctic Climate of the Past Discussions, 8, 1169-1207, 2012 Author(s): B. Chapligin, H. Meyer, G. E. A. Swann, C. Meyer-Jacob, and H.-W. Hubberten In 2003 sediment core Lz1024 was drilled at Lake El'gygytgyn, far east Russian Arctic, in an area of the Northern Hemisphere which has not been glaciated for the last 3.6 Ma. Biogenic silica was used for analysing the oxygen isotope composition (δ 18 O diatom ) in the upper 13 m long section dating back about 250 ka with samples dominated by one taxa in the

Beschreibung: Global distributions of C 2 H 6 , C 2 H 2 , HCN, and PAN retrieved from MIPAS reduced spectral resolution measurements Atmospheric Measurement Techniques, 5, 723-734, 2012 Author(s): A. Wiegele, N. Glatthor, M. Höpfner, U. Grabowski, S. Kellmann, A. Linden, G. Stiller, and T. von Clarmann Vertical profiles of mixing ratios of C 2 H 6 , C 2 H 2 , HCN, and PAN were retrieved from MIPAS reduced spectral resolution nominal mode limb emission measurements. The retrieval strategy follows that of the analysis of MIPAS high resolution measurements, with occasional adjustments to cope with the reduced spectral resolution under which MIPAS is operated since 2005. MIPAS measurements from January 2005 to January 2010 have been analyzed with special emphasis on October 2007. Largest mixing ratios are found in the troposphere, and reach 1.2 ppbv for C 2 H 6 , 1 ppbv for HCN, 600 pptv for PAN, and 450 pptv for C 2 H 2 . The estimated precisions in case of significantly enhanced mixing ratios (including measurement noise and propagation of uncertain parameters randomly varying in the time domain) and altitude resolution are typically 10%, 3–4.5 km for C 2 H 6 , 15%, 4–6 km for HCN, 6%, 2.5–3.5 km for PAN, and 7%, 2.5–4 km for C 2 H 2 .

Beschreibung: A model-data comparison for a multi-model ensemble of early Eocene atmosphere-ocean simulations: EoMIP Climate of the Past Discussions, 8, 1229-1273, 2012 Author(s): D. J. Lunt, T. Dunkley Jones, M. Heinemann, M. Huber, A. LeGrande, A. Winguth, C. Loptson, J. Marotzke, J. Tindall, P. Valdes, and C. Winguth The early Eocene (~55 to 50 Ma) is a time period which has been explored in a large number of modelling and data studies. Here, using an ensemble of previously published model results, making up "EoMIP" – the Eocene Modelling Intercomparison Project, and syntheses of early Eocene terrestrial and SST temperature data, we present a self-consistent inter-model and model-data comparison. This shows that the previous modelling studies exhibit a very wide inter-model variability, but that at high CO 2 , there is good agreement between models and data for this period, particularly if possible seasonal biases in some of the proxies are considered. An energy balance analysis explores the reasons for the differences between the model results, and suggests that differences in surface albedo feedbacks, water vapour and lapse rate feedbacks, and prescribed aerosol loading are the dominant cause for the different results seen in the models, rather than inconsistencies in other prescribed boundary conditions or differences in cloud feedbacks. The CO 2 level which would give optimal early Eocene model-data agreement, based on those models which have carried out simulations with more than one CO 2 level, is in the range 2000 ppmv to 6500 ppmv. Given the spread of model results, tighter bounds on proxy estimates of atmospheric CO 2 during this time period will allow a quantitative assessment of the skill of the models at simulating warm climates, which could be used as a metric for weighting future climate predictions.

Beschreibung: "OAE 3" – a low- to mid-latitude Atlantic oceanic event during the Coniacian-Santonian Climate of the Past Discussions, 8, 1209-1227, 2012 Author(s): M. Wagreich The Coniacian-Santonian time interval is the inferred time of oceanic anoxic event 3 (OAE 3), the last of the Cretaceous OAEs. A detailed look on the temporal and spatial distribution of organic-rich deposits attributed to OAE 3 suggests that black shale occurrences are restricted to the equatorial to mid-latitudinal Atlantic and adjacent basins, shelves and epicontinental seas like parts of the Caribbean, the Maracaibo Basin and the Western Interior Basin, and are largely absent in the Tethys, the North Atlantic, the southern South Atlantic, and the Pacific. Here, oxic bottom waters prevailed as indicated by the widespread occurrence of red deep-marine CORBs (Cretaceous Oceanic Red Beds). Widespread CORB sedimentation started during the Turonian after Oceanic Anoxic Event 2 (OAE 2) except in the Atlantic realm where organic-rich strata continue up to the Santonian. The temporal distribution of black shales attributed to OAE 3 indicates that organic-rich strata do not define a single and distinct short-time event, but are distributed over a longer time span and occur in different basins during different times. This suggests intermittent and regional anoxic conditions from the Coniacian to the Santonian. A comparison of time-correlated high-resolution δ 13 C curves for this interval indicates several minor positive excursions of about 0.5 permil, probably as a result of massive organic carbon burial cycles in the Atlantic. Regional wind-induced upwelling and silled deep basins may have contributed to the development of anoxia during a global oxic time interval, thus highlighting the regional character of inferred OAE 3 as an Atlantic anoxic event (AAE).

Beschreibung: DOAS measurements of NO 2 from an ultralight aircraft during the Earth Challenge expedition Atmospheric Measurement Techniques, 5, 2057-2068, 2012 Author(s): A. Merlaud, M. Van Roozendael, J. van Gent, C. Fayt, J. Maes, X. Toledo-Fuentes, O. Ronveaux, and M. De Mazière We report on airborne Differential Optical Absorption Spectroscopy (DOAS) measurements of NO 2 tropospheric columns above South Asia, the Arabic peninsula, North Africa, and Italy in November and December 2009. The DOAS instrument was installed on an ultralight aircraft involved in the Earth Challenge project, an expedition of seven pilots flying on four ultralight aircraft between Australia and Belgium. The instrument recorded spectra in limb geometry with a large field of view, a set-up which provides a high sensitivity to the boundary layer NO 2 while minimizing the uncertainties related to the attitude variations. We compare our measurements with OMI (Ozone Monitoring Instrument) and GOME-2 (Global Ozone Monitoring Experiment 2) tropospheric NO 2 products when the latter are available. Above Rajasthan and the Po Valley, two areas where the NO 2 field is homogeneous, data sets agree very well. Our measurements in these areas are 0.1 ± 0.1 to 3 ± 1 × 10 15 molec cm −2 and 2.6 ± 0.8 × 10 16 molec cm −2 , respectively. Flying downwind of Riyadh, our NO 2 measurements show the structure of the megacity's exhaust plume with a higher spatial resolution than OMI. Moreover, our measurements are larger (up to 40%) than those seen by satellites. We also derived tropospheric columns when no satellite data were available if it was possible to get information on the visibility from satellite measurements of aerosol optical thickness. This experiment also provides a confirmation for the recent finding of a soil signature above desert.

Beschreibung: Investigating the past and recent δ 18 O-accumulation relationship seen in Greenland ice cores Climate of the Past Discussions, 8, 4105-4120, 2012 Author(s): S. L. Buchardt, H. B. Clausen, B. M. Vinther, and D. Dahl-Jensen Decadal means of δ 18 O and accumulation rates from 52 ice core sites in Greenland are presented. The accumulation rates are derived from annual layers determined in the δ 18 O curve. Investigation of the δ 18 O-accumulation relationship across the ice divide reveals a significant Foehn effect with anticorrelation of δ 18 O and accumulation on the lee side of the divide in Southern Greenland, while no effect is seen in Central Greenland. Furthermore, the sensitivity of accumulation rate to changes in temperature is found to be smaller in Northern Greenland than in the central and southern parts. Four sites in the data set contain sufficient recent data that the period of observed temperature rise from the 1990's and onwards can be investigated. All four sites are located close to the ice divide in Northern Greenland and while three sites show increased temperatures, none show evidence of increased accumulation.

Beschreibung: Vegetation dynamics in the Northeastern Mediterranean region during the past 23 000 yr: insight from a new pollen record from the Sea of Marmara (core MD01-2430) Climate of the Past Discussions, 8, 4183-4221, 2012 Author(s): V. Valsecchi, M. F. Sanchez Goñi, and L. Londeix High-resolution pollen analysis of core MD01-2430 from the Sea of Marmara (40°47.81′ N, 27°43.51′ E) allows us to reconstruct the vegetation response to climatic changes during the past 23 cal ka in the Northeastern Mediterranean. Variation in mesic/temperate forest cover indicates major climatic shifts connected to Heinrich Stadial 1, Bölling-Allerød, Younger Dryas and to the onset of the Holocene. Pollen-anthropogenic indicator approach was used to recognize human-induced landscape changes in the Sea of Marmara. The pollen-inferred onset of the Holocene occurs at ca. 11.5 cal ka, indicating that the Northeastern Mediterranean region represents a transitional zone where higher moisture availability supported an earlier forest expansion than the borderlands of the Aegean Sea and Black Sea. Three major forest retreats occurred during the Holocene at ca. 9.2, 5.5, and 2.1 cal ka while a weaker forest setback was detected at 7.9 cal ka. The Holocene forest setbacks are in phase with previously published alkenone-inferred sea-surface temperature decreases in the Sea of Marmara (core MD01-2430) reconstructed from the same archive. Our new pollen record testifies the sensitivity of Mediterranean forests to changes in moisture availability which is driven by changes in high-latitude climate drivers (North Atlantic Oscillations and/or Siberian High).

Beschreibung: Evaluating nighttime CALIOP 0.532 μm aerosol optical depth and extinction coefficient retrievals Atmospheric Measurement Techniques, 5, 2143-2160, 2012 Author(s): J. R. Campbell, J. L. Tackett, J. S. Reid, J. Zhang, C. A. Curtis, E. J. Hyer, W. R. Sessions, D. L. Westphal, J. M. Prospero, E. J. Welton, A. H. Omar, M. A. Vaughan, and D. M. Winker NASA Cloud Aerosol Lidar with Orthogonal Polarization (CALIOP) Version 3.01 5-km nighttime 0.532 μm aerosol optical depth (AOD) datasets from 2007 are screened, averaged and evaluated at 1° × 1° resolution versus corresponding/co-incident 0.550 μm AOD derived using the US Navy Aerosol Analysis and Prediction System (NAAPS), featuring two-dimensional variational assimilation of quality-assured NASA Moderate Resolution Imaging Spectroradiometer (MODIS) and Multi-angle Imaging Spectroradiometer (MISR) AOD. In the absence of sunlight, since passive radiometric AOD retrievals rely overwhelmingly on scattered radiances, the model represents one of the few practical global estimates available from which to attempt such a validation. Daytime comparisons, though, provide useful context. Regional-mean CALIOP vertical profiles of night/day 0.532 μm extinction coefficient are compared with 0.523/0.532 μm ground-based lidar measurements to investigate representativeness and diurnal variability. In this analysis, mean nighttime CALIOP AOD are mostly lower than daytime (0.121 vs. 0.126 for all aggregated data points, and 0.099 vs. 0.102 when averaged globally per normalised 1° × 1° bin), though the relationship is reversed over land and coastal regions when the data are averaged per normalised bin (0.134/0.108 vs. 0140/0.112, respectively). Offsets assessed within single bins alone approach ±20%. CALIOP AOD, both day and night, are higher than NAAPS over land (0.137 vs. 0.124) and equal over water (0.082 vs. 0.083) when averaged globally per normalised bin. However, for all data points inclusive, NAAPS exceeds CALIOP over land, coast and ocean, both day and night. Again, differences assessed within single bins approach 50% in extreme cases. Correlation between CALIOP and NAAPS AOD is comparable during both day and night. Higher correlation is found nearest the equator, both as a function of sample size and relative signal magnitudes inherent at these latitudes. Root mean square deviation between CALIOP and NAAPS varies between 0.1 and 0.3 globally during both day/night. Averaging of CALIOP along-track AOD data points within a single NAAPS grid bin improves correlation and RMSD, though day/night and land/ocean biases persist and are believed systematic. Vertical profiles of extinction coefficient derived in the Caribbean compare well with ground-based lidar observations, though potentially anomalous selection of a priori lidar ratios for CALIOP retrievals is likely inducing some discrepancies. Mean effective aerosol layer top heights are stable between day and night, indicating consistent layer-identification diurnally, which is noteworthy considering the potential limiting effects of ambient solar noise during day.

Beschreibung: The scientific basis for a satellite mission to retrieve CCN concentrations and their impacts on convective clouds Atmospheric Measurement Techniques, 5, 2039-2055, 2012 Author(s): D. Rosenfeld, E. Williams, M. O. Andreae, E. Freud, U. Pöschl, and N. O. Rennó The cloud-mediated aerosol radiative forcing is widely recognized as the main source of uncertainty in our knowledge of the anthropogenic forcing on climate. The current challenges for improving our understanding are (1) global measurements of cloud condensation nuclei (CCN) in the cloudy boundary layer from space, and (2) disentangling the effects of aerosols from the thermodynamic and meteorological effects on the clouds. Here, we present a new conceptual framework to help us overcome these two challenges, using relatively simple passive satellite measurements in the visible and infared (IR). The idea is to use the clouds themselves as natural CCN chambers by retrieving simultaneously the number of activated aerosols at cloud base, N a , and the cloud base updraft speed. The N a is obtained by analyzing the distribution of cloud drop effective radius in convective elements as a function of distance above cloud base. The cloud base updraft velocities are estimated by double stereoscopic viewing and tracking of the evolution of cloud surface features just above cloud base. In order to resolve the vertical dimension of the clouds, the field of view will be 100 m for the microphysical retrievals, and 50 m for the stereoscopic measurements. The viewing geometry will be eastward and 30 degrees off nadir, with the Sun in the back at 30 degrees off zenith westward, requiring a Sun-synchronous orbit at 14 LST. Measuring simultaneously the thermodynamic environment, the vertical motions of the clouds, their microstructure and the CCN concentration will allow separating the dynamics from the CCN effects. This concept is being applied in the proposed satellite mission named Clouds, Hazards and Aerosols Survey for Earth Researchers (CHASER).

Beschreibung: Temperature response to external forcing in simulations and reconstructions of the last millennium Climate of the Past Discussions, 8, 4003-4073, 2012 Author(s): L. Fernández-Donado, J. F. González-Rouco, C. C. Raible, C. M. Ammann, D. Barriopedro, E. García-Bustamante, J. H. Jungclaus, S. J. Lorenz, J. Luterbacher, S. J. Phipps, J. Servonnat, D. Swingedouw, S. F. B. Tett, S. Wagner, P. Yiou, and E. Zorita The understanding of natural climate variability and its driving factors is crucial to assess future climate change. Therefore, comparing proxy-based climate reconstructions with forcing factors as well as comparing these with paleoclimate model simulations is key to gain insights into the relative roles of internal versus forced variability. A review of the state of modeling of the last millennium climate previous to the CMIP5-PMIP3 coordinated effort is presented and compared to the available temperature reconstructions. Simulations and reconstructions broadly agree on reproducing the major temperature changes and suggest an overall linear response to external forcing on multidecadal or longer timescales. Internal variability is found to have an important influence at hemispheric and global scales. The spatial distribution of simulated temperature changes during the transition of the Medieval Climate Anomaly to the Little Ice Age disagrees with that found in the reconstructions, thus advocating for internal variability as a possible major player in shaping temperature changes through the millennium. A paleo transient climate response (PTCR) is defined to provide a quantitative framework for analysing the consistency between simulated and reconstructed climate. Beyond an overall agreement between simulated and reconstructed PTCR ranges, this analysis is able to single out specific discrepancies between some reconstructions and the ensemble of simulations. The disagreement is found in the cases where the reconstructions show reduced covariability with external forcings or when they present high rates of temperature change.

Beschreibung: Mismatch between the depth habitat of planktonic foraminifera and the calibration depth of SST transfer functions may bias reconstructions Climate of the Past Discussions, 8, 4075-4103, 2012 Author(s): R. J. Telford, C. Li, and M. Kucera We demonstrate that the temperature signal in the planktonic foraminifera assemblage data from the North Atlantic typically does not originate from near surface waters and argue that this has the potential to bias sea surface temperature reconstructions using transfer functions calibrated against near surface temperatures if the thermal structure of the upper few hundred metres of ocean changes over time. CMIP5 climate models indicate that ocean thermal structure in the N Atlantic changed between the Last Glacial Maximum (LGM) and the pre-industrial (PI), with some regions, mainly in the tropics, of the LGM ocean lacking good thermal analogues in the PI. Transfer functions calibrated against different depths reconstruct a marked subsurface cooling in the tropical Atlantic during the last glacial, in contrast to previous studies that reconstructed only a modest cooling. These possible biases in temperatures reconstructions may affect estimates of climate sensitivity based on the difference between LGM and pre-industrial climate. Quantifying these biases has the potential to alter our understanding of Last Glacial Maximum climate and improve estimates of climate sensitivity.

Beschreibung: Evaluation of continuous water vapor δD and δ 18 O measurements by off-axis integrated cavity output spectroscopy Atmospheric Measurement Techniques, 5, 2069-2080, 2012 Author(s): N. Kurita, B. D. Newman, L. J. Araguas-Araguas, and P. Aggarwal Recent commercially available laser spectroscopy systems enabled us to continuously and reliably measure the δD and δ 18 O of atmospheric water vapor. The use of this new technology is becoming popular because of its advantages over the conventional approach based on cold trap collection. These advantages include much higher temporal resolution/continuous monitoring and the ability to make direct measurements of both isotopes in the field. Here, we evaluate the accuracy and precision of the laser based water vapor isotope instrument through a comparison of measurements with those found using the conventional cold trap method. A commercially available water vapor isotope analyzer (WVIA) with the vaporization system of a liquid water standard (Water Vapor Isotope Standard Source, WVISS) from Los Gatos Research (LGR) Inc. was used for this study. We found that the WVIA instrument can provide accurate results if (1) correction is applied for time-dependent isotope drift, (2) normalization to the VSMOW/SLAP scale is implemented, and (3) the water vapor concentration dependence of the isotopic ratio is also corrected. In addition, since the isotopic value of water vapor generated by the WVISS is also dependent on the concentration of water vapor, this effect must be considered to determine the true water vapor concentration effect on the resulting isotope measurement. To test our calibration procedure, continuous water vapor isotope measurements using both a laser instrument and a cold trap system were carried out at the IAEA Isotope Hydrology Laboratory in Vienna from August to December 2011. The calibrated isotopic values measured using the WVIA agree well with those obtained via the cold trap method. The standard deviation of the isotopic difference between both methods is about 1.4‰ for δD and 0.28‰ for δ 18 O. This precision allowed us to obtain reliable values for d -excess. The day-to-day variation of d -excess measured by WVIA also agrees well with that found using the cold trap method. These results demonstrate that a coupled system, using commercially available WVIA and WVISS instruments can provide continuous and accurate isotope data, with results achieved similar to those obtained using the conventional method, but with drastically improved temporal resolution.

Beschreibung: A disjunct eddy accumulation system for the measurement of BVOC fluxes: instrument characterizations and field deployment Atmospheric Measurement Techniques, 5, 2115-2132, 2012 Author(s): G. D. Edwards, D. K. Martins, T. Starn, K. Pratt, and P. B. Shepson Biological volatile organic compounds (BVOCs), such as isoprene and monoterpenes, are emitted in large amounts from forests. Quantification of the flux of BVOCs is critical in the evaluation of the impact of these compounds on the concentrations of atmospheric oxidants and on the production of secondary organic aerosol. A disjunct eddy accumulation (DEA) sampler system was constructed for the measurement of speciated BVOC fluxes. Unlike traditional eddy covariance (EC), the relatively new technique of disjunct sampling differs by taking short, discrete samples that allow for slower sampling frequencies. Disjunct sample airflow is directed into cartridges containing sorbent materials at sampling rates proportional to the magnitude of the vertical wind. Compounds accumulated on the cartridges are then quantified by thermal desorption and gas chromatography. Herein, we describe our initial tests to evaluate the disjunct sampler including the application of vertical wind measurements to create optimized sampling thresholds. Measurements of BVOC fluxes obtained from DEA during its deployment above a mixed hardwood forest at the University of Michigan Biological Station (Pellston, MI) during the 2009 CABINEX field campaign are reported. Daytime (09:00 a.m. to 05:00 p.m. LT) isoprene fluxes, when averaged over the footprint of the tower, were 1.31 mg m −2 h −1 which are comparable to previous flux measurements at this location. Speciated monoterpene fluxes are some of the first to be reported from this site. Daytime averages were 26.7 μg m −2 h −1 for α-pinene and 10.6 μg m −2 h −1 for β-pinene. These measured concentrations and fluxes were compared to the output of an atmospheric chemistry model, and were found to be consistent with our knowledge of the variables that control BVOCs fluxes at this site.

Beschreibung: Validation of six years of SCIAMACHY carbon monoxide observations using MOZAIC CO profile measurements Atmospheric Measurement Techniques, 5, 2133-2142, 2012 Author(s): A. T. J. de Laat, R. Dijkstra, H. Schrijver, P. Nédélec, and I. Aben This paper presents a validation study of SCanning Imaging Absorption SpectroMeter for Atmospheric CartograpHY (SCIAMACHY) carbon monoxide (CO) total column measurements from the Iterative Maximum Likelihood Method (IMLM) algorithm using vertically integrated profile aircraft measurements obtained within the MOZAIC project for the six year time period of 2003–2008. Overall we find a good agreement between SCIAMACHY and airborne measurements for both mean values – also on a year-to-year basis – as well as seasonal variations. Several locations show large biases that are attributed to local effects like orography and proximity of large emission sources. Differences were detected for individual years: 2003, 2004 and 2006 have larger biases than 2005, 2007 and 2008, which appear to be related to SCIAMACHY instrumental issues but require more research. Results from this study are consistent with, and complementary to, findings from a previous validation study using ground-based measurements (de Laat et al., 2010b). According to this study, the SCIAMACHY data, if individual measurements are of sufficient quality – good signal-to-noise, can be used to determine the spatial distribution and seasonal cycles of CO total columns over clean areas. Biases found over areas with strong emissions (Africa, China) could be explained by low sensitivity of the instrument in the boundary layer and users are recommended to avoid using the SCIAMACHY data while trying to quantify CO burden and/or retrieve CO emissions in such areas.

Beschreibung: Variability of the ocean heat content during the last millennium – an assessment with the ECHO-g Model Climate of the Past Discussions, 8, 4223-4267, 2012 Author(s): P. Ortega, M. Montoya, F. González-Rouco, H. Beltrami, and D. Swingedouw Studies addressing climate variability during the last millennium generally focus on variables with a direct influence on climate variability, like the fast thermal response to varying radiative forcing, or the large-scale changes in atmospheric dynamics (e.g. North Atlantic Oscillation). The ocean responds to these variations by slowly integrating in depth the upper heat flux changes, thus producing a delayed influence on ocean heat content (OHC) that can latter impact on low frequency SST variability through reemergence processes. In this study, both the externally and internally driven variations of the OHC are investigated during the last millennium using a set of fully coupled simulations using the model ECHO-G. When compared to observations for the last 55 yr, the model tends to overestimate the global trends, and underestimate the decadal OHC variability. Extending the analysis back to the last one thousand years, the main impact of the radiative forcing is an OHC increase at high latitudes, explained to some extent by a reduction in cloud cover and the subsequent increase of short-wave radiation at the surface. This OHC response is dominated by the effect of volcanism in the preindustrial era, and by the fast increase of GHGs during the last 150 yr. Likewise, salient impacts from internal climate variability are observed at regional scales. For instance, upper temperature in the Equatorial Pacific is controlled by ENSO variability from interannual to multidecadal timescales. Also, both the Pacific Decadal Oscillation (PDO) and the Atlantic Multidecadal Oscillation (AMO) modulate intermittently the interdecadal OHC variability in the North Pacific and Mid Atlantic, respectively. The NAO, through its influence on North Atlantic surface heat fluxes and convection, also plays an important role on the OHC at multiple timescales, leading first to a cooling in the Labrador and Irminger seas, and later on to a North Atlantic warming, associated with a delayed impact on the AMO.

Beschreibung: Corrigendum to "Trend analysis of aerosol optical thickness and Ångström exponent derived from the global AERONET spectral observations" published in Atmos. Meas. Tech., 5, 1271–1299, 2012 Atmospheric Measurement Techniques, 5, 2113-2113, 2012 Author(s): J. Yoon, W. von Hoyningen-Huene, A. A. Kokhanovsky, M. Vountas, and J. P. Burrows No abstract available.

Beschreibung: Using sonic anemometer temperature to measure sensible heat flux in strong winds Atmospheric Measurement Techniques, 5, 2095-2111, 2012 Author(s): S. P. Burns, T. W. Horst, L. Jacobsen, P. D. Blanken, and R. K. Monson Sonic anemometers simultaneously measure the turbulent fluctuations of vertical wind ( w ') and sonic temperature ( T s '), and are commonly used to measure sensible heat flux ( H ). Our study examines 30-min heat fluxes measured with a Campbell Scientific CSAT3 sonic anemometer above a subalpine forest. We compared H calculated with T s to H calculated with a co-located thermocouple and found that, for horizontal wind speed ( U ) less than 8 m s −1 , the agreement was around ±30 W m −2 . However, for U ≈ 8 m s −1 , the CSAT H had a generally positive deviation from H calculated with the thermocouple, reaching a maximum difference of ≈250 W m −2 at U ≈ 18 m s −1 . With version 4 of the CSAT firmware, we found significant underestimation of the speed of sound and thus T s in high winds (due to a delayed detection of the sonic pulse), which resulted in the large CSAT heat flux errors. Although this T s error is qualitatively similar to the well-known fundamental correction for the crosswind component, it is quantitatively different and directly related to the firmware estimation of the pulse arrival time. For a CSAT running version 3 of the firmware, there does not appear to be a significant underestimation of T s ; however, a T s error similar to that of version 4 may occur if the CSAT is sufficiently out of calibration. An empirical correction to the CSAT heat flux that is consistent with our conceptual understanding of the T s error is presented. Within a broader context, the surface energy balance is used to evaluate the heat flux measurements, and the usefulness of side-by-side instrument comparisons is discussed.

Beschreibung: Remote sensing of near-infrared chlorophyll fluorescence from space in scattering atmospheres: implications for its retrieval and interferences with atmospheric CO 2 retrievals Atmospheric Measurement Techniques, 5, 2081-2094, 2012 Author(s): C. Frankenberg, C. O'Dell, L. Guanter, and J. McDuffie With the advent of dedicated greenhouse gas space-borne spectrometers sporting high resolution spectra in the O 2 A-band spectral region (755–774 nm), the retrieval of chlorophyll fluorescence has become feasible on a global scale. If unaccounted for, however, fluorescence can indirectly perturb the greenhouse gas retrievals as it perturbs the oxygen absorption features. As atmospheric CO 2 measurements are used to invert net fluxes at the land–atmosphere interface, a bias caused by fluorescence can be crucial as it will spatially correlate with the fluxes to be inverted. Avoiding a bias and retrieving fluorescence accurately will provide additional constraints on both the net and gross fluxes in the global carbon cycle. We show that chlorophyll fluorescence, if neglected, systematically interferes with full-physics multi-band X CO 2 retrievals using the O 2 A-band. Systematic biases in X CO 2 can amount to +1 ppm if fluorescence constitutes 1% to the continuum level radiance. We show that this bias can be largely eliminated by simultaneously fitting fluorescence in a full-physics based retrieval. If fluorescence is the primary target, a dedicated but very simple retrieval based purely on Fraunhofer lines is shown to be more accurate and very robust even in the presence of large scattering optical depths. We find that about 80% of the surface fluorescence is retained at the top-of-atmosphere, even for cloud optical thicknesses around 2–5. We further show that small instrument modifications to future O 2 A-band spectrometer spectral ranges can result in largely reduced random errors in chlorophyll fluorescence, paving the way towards a more dedicated instrument exploiting solar absorption features only.

Beschreibung: Historical and idealized climate model experiments: an EMIC intercomparison Climate of the Past Discussions, 8, 4121-4181, 2012 Author(s): M. Eby, A. J. Weaver, K. Alexander, K. Zickfeld, A. Abe-Ouchi, A. A. Cimatoribus, E. Crespin, S. S. Drijfhout, N. R. Edwards, A. V. Eliseev, G. Feulner, T. Fichefet, C. E. Forest, H. Goosse, P. B. Holden, F. Joos, M. Kawamiya, D. Kicklighter, H. Kienert, K. Matsumoto, I. I. Mokhov, E. Monier, S. M. Olsen, J. O. P. Pedersen, M. Perrette, G. Philippon-Berthier, A. Ridgwell, A. Schlosser, T. Schneider von Deimling, G. Shaffer, R. S. Smith, R. Spahni, A. P. Sokolov, M. Steinacher, K. Tachiiri, K. Tokos, M. Yoshimori, N. Zeng, and F. Zhao Both historical and idealized climate model experiments are performed with a variety of Earth System Models of Intermediate Complexity (EMICs) as part of a community contribution to the Intergovernmental Panel on Climate Change Fifth Assessment Report. Historical simulations start at 850 CE and continue through to 2005. The standard simulations include changes in forcing from solar luminosity, Earth's orbital configuration, CO 2 , additional greenhouse gases, land-use, and sulphate and volcanic aerosols. In spite of very different modelled pre-industrial global surface air temperatures, overall 20th century trends in surface air temperature and carbon uptake are reasonably well simulated when compared to observed trends. Land carbon fluxes show much more variation between models than ocean carbon fluxes, and recent land fluxes seem to be underestimated. It is possible that recent modelled climate trends or climate-carbon feedbacks are overestimated resulting in too much land carbon loss or that carbon uptake due to CO 2 and/or nitrogen fertilization is underestimated. Several one thousand year long, idealized, 2x and 4x CO 2 experiments are used to quantify standard model characteristics, including transient and equilibrium climate sensitivities, and climate-carbon feedbacks. The values from EMICs generally fall within the range given by General Circulation Models. Seven additional historical simulations, each including a single specified forcing, are used to assess the contributions of different climate forcings to the overall climate and carbon cycle response. The response of surface air temperature is the linear sum of the individual forcings, while the carbon cycle response shows considerable synergy between land-use change and CO 2 forcings for some models. Finally, the preindustrial portions of the last millennium simulations are used to assess historical model carbon-climate feedbacks. Given the specified forcing, there is a tendency for the EMICs to underestimate the drop in surface air temperature and CO 2 between the Medieval Climate Anomaly and the Little Ice Age estimated from paleoclimate reconstructions. This in turn could be a result of errors in the reconstructions of volcanic and/or solar radiative forcing used to drive the models or the incomplete representation of certain processes or variability within the models. Given the datasets used in this study, the models calculate significant land-use emissions over the pre-industrial. This implies that land-use emissions might need to be taken into account, when making estimates of climate-carbon feedbacks from paleoclimate reconstructions.

Beschreibung: Dansgaard-Oeschger events: tipping points in the climate system Climate of the Past Discussions, 8, 4269-4294, 2012 Author(s): A. A. Cimatoribus, S. S. Drijfhout, V. Livina, and G. van der Schrier The largest variability in temperature over the last sixty thousand years is connected with Dansgaard-Oeschger events. Various prototype models have been proposed to explain these rapid climate fluctuations, but until now no observational constraint has been forwarded to choose between different theories. We assess the bimodality of the system reconstructing the topology of the multi-dimensional attractor over which the climate system evolves. Furthermore, we show that Dansgaard-Oeschger events are compatible with the crossing of a tipping point in the climate system. We use high-resolution ice core isotope data to investigate the statistical properties of the climate fluctuations in the period before the onset of the abrupt change. We find that the statistics are consistent with the switches between two different climate equilibrium states in response to a changing external forcing.

Beschreibung: Model sensitivity to North Atlantic freshwater forcing at 8.2 ka Climate of the Past Discussions, 8, 3949-3976, 2012 Author(s): C. Morrill, A. N. LeGrande, H. Renssen, P. Bakker, and B. L. Otto-Bliesner We compared four simulations of the 8.2 ka event to assess climate model sensitivity and skill in responding to North Atlantic freshwater perturbations. All of the simulations used the same freshwater forcing, 2.5 Sv for one year, applied to either the Hudson Bay or Labrador Sea. This freshwater pulse induced a decadal-mean slowdown of 10–25% in the Atlantic Meridional Overturning Circulation (AMOC) of the models and caused a large-scale pattern of climate anomalies that matched proxy evidence for cooling in the Northern Hemisphere and a southward shift of the Intertropical Convergence Zone. The multi-model ensemble generated temperature anomalies that were just half as large as those from quantitative proxy reconstructions, however. Also, the duration of AMOC and climate anomalies in three of the simulations was only several decades, significantly shorter than the duration of ~150 yr in the paleoclimate record. Possible reasons for these discrepancies include incorrect representation of the early Holocene climate and ocean state in the North Atlantic and uncertainties in the freshwater forcing estimates.

Beschreibung: Controls of Caribbean surface hydrology during the mid- to late Holocene: insights from monthly resolved coral records Climate of the Past Discussions, 8, 3901-3948, 2012 Author(s): C. Giry, T. Felis, M. Kölling, W. Wei, G. Lohmann, and S. Scheffers Here we reconstruct seasonality and interannual to multidecadal variability of sea surface hydrology of the southern Caribbean Sea by applying paired coral Sr/Ca and δ 18 O measurements on fossil annually-banded Diploria strigosa corals from Bonaire. This allows for better understanding short-term (i.e., seasonal to multidecadal) variability of the Caribbean hydrological cycle during the mid- to late Holocene. The monthly-resolved coral Δ δ 18 O records are used as a proxy for the oxygen isotopic composition of seawater (δ 18 O sw ) of the southern Caribbean Sea. Consistent with modern day conditions, annual δ 18 O sw cycles reconstructed from three modern corals reveal that freshwater budget at the study site is influenced by both the evaporation/precipitation ratio and the seasonal advection of tropical freshwater brought by wind-driven surface currents. In contrast, the annual δ 18 O sw cycle reconstructed from a mid-Holocene coral indicates sharp peaks towards more negative values in summer suggesting intense summer precipitation at 6 ka before present (BP). In line with this our model simulations indicate that increased seasonality of the hydrological cycle at 6 ka BP results from enhanced precipitation in summertime. On interannual to multidecadal timescales, the systematic positive correlation observed between reconstructed sea surface temperature and salinity suggests that freshwater discharged from the Orinoco and Amazon rivers and transported into the Caribbean by wind-driven surface currents is a critical component influencing sea surface hydrology on these timescales.

Beschreibung: Airborne intercomparison of HO x measurements using laser-induced fluorescence and chemical ionization mass spectrometry during ARCTAS Atmospheric Measurement Techniques, 5, 2025-2037, 2012 Author(s): X. Ren, J. Mao, W. H. Brune, C. A. Cantrell, R. L. Mauldin III, R. S. Hornbrook, E. Kosciuch, J. R. Olson, J. H. Crawford, G. Chen, and H. B. Singh The hydroxyl (OH) and hydroperoxyl (HO 2 ) radicals, collectively called HO x , play central roles in tropospheric chemistry. Accurate measurements of OH and HO 2 are critical to examine our understanding of atmospheric chemistry. Intercomparisons of different techniques for detecting OH and HO 2 are vital to evaluate their measurement capabilities. Three instruments that measured OH and/or HO 2 radicals were deployed on the NASA DC-8 aircraft throughout Arctic Research of the Composition of the Troposphere from Aircraft and Satellites (ARCTAS) in the spring and summer of 2008. One instrument was the Penn State Airborne Tropospheric Hydrogen Oxides Sensor (ATHOS) for OH and HO 2 measurements based on Laser-Induced Fluorescence (LIF) spectroscopy. A second instrument was the NCAR Selected-Ion Chemical Ionization Mass Spectrometer (SI-CIMS) for OH measurement. A third instrument was the NCAR Peroxy Radical Chemical Ionization Mass Spectrometer (PeRCIMS) for HO 2 measurement. Formal intercomparison of LIF and CIMS was conducted for the first time on a same aircraft platform. The three instruments were calibrated by quantitative photolysis of water vapor by ultraviolet (UV) light at 184.9 nm with three different calibration systems. The absolute accuracies were ±32% (2σ) for the LIF instrument, ±65% (2σ) for the SI-CIMS instrument, and ±50% (2σ) for the PeRCIMS instrument. In general, good agreement was obtained between the CIMS and LIF measurements of both OH and HO 2 measurements. Linear regression of the entire data set yields [OH] CIMS = 0.89 × [OH] LIF + 2.8 × 10 4 cm −3 with a correlation coefficient r 2 = 0.72 for OH, and [HO 2 ] CIMS = 0.86 × [HO 2 ] LIF + 3.9 parts per trillion by volume (pptv, equivalent to pmol mol −1 ) with a correlation coefficient r 2 = 0.72 for HO 2 . In general, the difference between CIMS and LIF instruments for OH and HO 2 measurements can be explained by their combined measurement uncertainties. Comparison with box model results shows some similarities for both the CIMS and LIF measurements. First, the observed-to-modeled HO 2 ratio increases greatly for higher NO mixing ratios, indicating that the model may not properly account for HO x sources that correlate with NO. Second, the observed-to-modeled OH ratio increases with increasing isoprene mixing ratios, suggesting either incomplete understanding of isoprene chemistry in the model or interferences in the measurements in environments where biogenic emissions dominate ambient volatile organic compounds.

Beschreibung: Consistency between Fourier transform and small-volume few-wave decomposition for spectral and spatial variability of gravity waves above a typhoon Atmospheric Measurement Techniques, 5, 1637-1651, 2012 Author(s): C. I. Lehmann, Y.-H. Kim, P. Preusse, H.-Y. Chun, M. Ern, and S.-Y. Kim Convective gravity wave (GW) sources are spatially localized and emit at the same time waves with a wide spectrum of phase speeds. Any wave analysis therefore compromises between spectral and spatial resolution. Future satellite borne limb imagers will for a first time provide real 3-D volumes of observations. These volumes will be however limited which will impose further constraints on the analysis technique. In this study a three dimensional few-wave approach fitting sinusoidal waves to limited 3-D volumes is introduced. The method is applied to simulated GWs above typhoon Ewiniar and GW momentum flux is estimated from temperature fluctuations. Phase speed spectra as well as average profiles of positive, negative and net momentum fluxes are compared to momentum flux estimated by Fourier transform as well as spatial averaging of wind fluctuations. The results agree within 10–20%. The few-wave method can also reveal the spatial orientation of the GWs with respect to the source. The relevance of the results for different types of measurements as well as its applicability to model data is discussed.

Beschreibung: Satellite retrieval of the liquid water fraction in tropical clouds between −20 and −38 °C Atmospheric Measurement Techniques, 5, 1683-1698, 2012 Author(s): D. L. Mitchell and R. P. d'Entremont This study describes a satellite remote sensing method for directly retrieving the liquid water fraction in mixed phase clouds, and appears unique in this respect. The method uses MODIS split-window channels for retrieving the liquid fraction from cold clouds where the liquid water fraction is less than 50% of the total condensate. This makes use of the observation that clouds only containing ice exhibit effective 12-to-11 μm absorption optical thickness ratios (β eff ) that are quasi-constant with retrieved cloud temperature T . This observation was made possible by using two CO 2 channels to retrieve T and then using the 12 and 11 μm channels to retrieve emissivities and β eff . Thus for T 〈 −40 °C, β eff is constant, but for T 〉 −40 °C, β eff slowly increases due to the presence of liquid water, revealing mean liquid fractions of ~ 10% around −22 °C from tropical clouds identified as cirrus by the cloud mask. However, the uncertainties for these retrievals are large, and extensive in situ measurements are needed to refine and validate these retrievals. Such liquid levels are shown to reduce the cloud effective diameter D e such that cloud optical thickness will increase by more than 50% for a given water path, relative to D e corresponding to pure ice clouds. Such retrieval information is needed for validation of the cloud microphysics in climate models. Since low levels of liquid water can dominate cloud optical properties, tropical clouds between −25 and −20 °C may be susceptible to the first aerosol indirect effect.

Beschreibung: Quantification of the Greenland ice sheet contribution to Last Interglacial sea-level rise Climate of the Past Discussions, 8, 2731-2776, 2012 Author(s): E. J. Stone, D. J. Lunt, J. D. Annan, and J. C. Hargreaves The Last Interglaciation (~ 130–115 thousand years ago) was a time when the Arctic climate was warmer than today (Anderson et al., 2006; Kaspar et al., 2005) and sea-level extremely likely at least 6 m higher (Kopp et al., 2009). However, there is large uncertainty in the relative contributions to this sea-level rise from the Greenland and Antarctic ice sheets and smaller icefields (Otto-Bliesner et al., 2006; Huybrechts, 2002; Letréguilly et al., 1991; Ritz et al., 1997; Cuffey and Marshall, 2000; Tarasov and Peltier, 2003; Lhomme et al., 2005; Greve, 2005; Robinson et al., 2011; Fyke et al., 2011). By performing an ensemble of 500 coupled climate – ice sheet model simulations, constrained by paleo-data, we determine probabilistically the likely contribution of Greenland ice sheet melt to Last Interglacial sea-level rise, taking into account model uncertainty. Here we show a 90% probability that Greenland ice melt contributed at least 0.6 m but less than 10% probability it exceeded 3.5 m, a value which is lower than several recent estimates (Cuffey and Marshall, 2000; Tarasov and Peltier, 2003; Lhomme et al., 2005; Robinson et al., 2011). Our combined modelling and paleo-data approach suggests that the Greenland ice sheet is less sensitive to orbital forcing than previously thought, and implicates Antarctic melt as providing a substantial contribution to Last Interglacial sea-level rise.

Beschreibung: An underestimated record breaking event: why summer 1540 was very likely warmer than 2003 Climate of the Past Discussions, 8, 2695-2730, 2012 Author(s): O. Wetter and C. Pfister This paper challenges the argument obtained from the analysis of grape harvest (GHD) and maximum latewood density (MXD) data that the 2003 heat-wave in Western Europe was the most extreme warm anomaly in the last millennium. We have evidence that the heat and drought in 1540 known from numerous contemporary narrative documentary reports is not adequately reflected in these estimates. Vines severely suffered from the extreme heat and drought which led vine-growers to postpone the harvest in hope for a rain spell. At the time of harvest many grapes had already become raisins. Likewise, many trees suffered from premature leaf fall probably as a result of a decreased net photosynthesis, as it was measured in 2003. To more realistically assess 1540's spring–summer (AMJJ) temperature we present a new Swiss series of critically evaluated GHD. Basing on three different approaches considering the drought effect on vines, temperatures were assessed between 4.3 °C and 6.3 °C (including the Standard Error of Estimate (SEE) of 0.52 °C) above the 1901–2000 mean which is significantly higher than the value of 2.9 °C measured in 2003. Considering the significance of soil moisture deficits for extreme heat-waves this result still needs to be validated with estimated seasonal precipitation from independent evidence.

Beschreibung: Reconstruction of drip-water δ 18 O based on calcite oxygen and clumped isotopes of speleothems from Bunker Cave (Germany) Climate of the Past Discussions, 8, 2853-2892, 2012 Author(s): T. Kluge, H. P. Affek, T. Marx, W. Aeschbach-Hertig, D. F. C. Riechelmann, D. Scholz, S. Riechelmann, A. Immenhauser, D. K. Richter, J. Fohlmeister, A. Wackerbarth, A. Mangini, and C. Spötl The geochemical signature of many speleothems used for reconstruction of past continental climates is affected by kinetic isotope fractionation. This limits quantitative paleoclimate reconstruction and, in cases where the kinetic fractionation varies with time, also affects relative paleoclimate interpretations. In carbonate archive research, clumped isotope thermometry is typically used as proxy for absolute temperatures. In the case of speleothems, however, clumped isotopes provide a sensitive indicator for disequilibrium effects. The extent of kinetic fractionation co-varies in Δ 47 and δ 18 O so that it can be used to account for disequilibrium in δ 18 O and to extract the past drip-water composition. Here we apply this approach to stalagmites from Bunker Cave (Germany) and calculate drip-water δ 18 O w values for the Eemian, Marine Isotope Stage (MIS) 3, and the Holocene, relying on independent temperature estimates and accounting for disequilibrium. Applying the co-variation method to modern calcite precipitates yields drip-water δ 18 O w values in agreement with modern cave drip-water δ 18 O w of −7.9 ± 0.3‰, despite large and variable disequilibrium effects in both calcite δ 18 O c and Δ 47 . Reconstructed paleo-drip-water δ 18 O w values are lower during colder periods (e.g., MIS 3: −8.5 ± 0.4‰ and the early Holocene at 11 kyr: −9.3 ± 0.1‰) and show higher values during warmer climatic periods (e.g., the Eemian: −7.5 ± 0.2‰ and the Holocene Climatic Optimum: −7.2 ± 0.3‰). This new approach offers a unique possibility for quantitative climate reconstruction including the assessment of past hydrological conditions while accounting for disequilibrium effects.

Beschreibung: Carbon monoxide measurements onboard the CARIBIC passenger aircraft using UV resonance fluorescence Atmospheric Measurement Techniques, 5, 1753-1760, 2012 Author(s): D. Scharffe, F. Slemr, C. A. M. Brenninkmeijer, and A. Zahn Goal of the project CARIBIC (Civil Aircraft for the Regular Investigation of the atmosphere Based on an Instrumented Container) is to carry out regular and detailed observations of atmospheric composition (particles and gases) at cruising altitudes of passenger aircraft, i.e. at 9–12 km. Continuous, fast measurement of CO is indispensable for the chemical characterization of encountered air masses, for the detection of plumes of polluted air and for studying troposphere-stratosphere transport. CO is measured by a commercial resonance fluorescence UV instrument modified for the use onboard passenger aircraft. Modifications were necessary to optimize the instrument reliability allowing unattended operation for several days. The instrument has a precision of 1–2 ppbv at an integration time of 1 s. The response time to reach 63.2% signal strength is 2 s. We describe the modifications of the instrument, the experiences made during its operation since December 2004, the quality control of CO measurements onboard CARIBIC, and suggest a regular service routine that guarantees long-term high-quality data.

Beschreibung: Stalagmite water content as a proxy for drip water supply in tropical and subtropical areas Climate of the Past Discussions, 8, 2893-2920, 2012 Author(s): N. Vogel, Y. Scheidegger, M. S. Brennwald, D. Fleitmann, S. Figura, R. Wieler, and R. Kipfer In this pilot study water was extracted from samples of two Holocene stalagmites from Socotra Island, Yemen, and one Eemian stalagmite from southern continental Yemen. The amount of water extracted per unit mass of stalagmite rock, termed "water yield" hereafter, serves as a measure for its total water content. The stalagmites' water yield records vary systematically with the corresponding oxygen isotopic compositions of the calcite (δ 18 O calcite ). Low δ 18 O calcite values are thereby accompanied by low water yields and vice versa. Based on the paleoclimatic interpretation of the δ 18 O calcite records, water yields can be linked to drip water supply. High drip water supply caused by high precipitation rates supports homogeneous deposition of calcite with low porosity and therefore a small fraction of water-filled inclusions, resulting in low water yields of the respective samples. A reduction of drip water supply fosters irregular growth of calcite with higher porosity, leading to an increase of the fraction of water-filled inclusions and thus higher water yields. The results are consistent with the literature on stalagmite growth and supported by optical inspection of thin sections of our samples. We propose that for a stalagmite from a tropical or subtropical area, its water yield record represents a novel paleoclimate proxy recording changes in drip water supply, which can in turn be interpreted in terms of associated precipitation rates.

Beschreibung: A 560 yr summer temperature reconstruction for the Western Mediterranean basin based on stable carbon isotopes from Pinus nigra ssp. laricio (Corsica/France) Climate of the Past Discussions, 8, 2111-2143, 2012 Author(s): S. Szymczak, M. M. Joachimski, A. Bräuning, T. Hetzer, and J. Kuhlemann The Mediterranean is considered as an area which will be affected strongly by current climate change. However, temperature records for the past centuries which can contribute to a better understanding of future climate changes are still sparse for this region. We established a network of multi-century stable carbon isotope chronologies on Corsica to study long-term climate variation in the Western Mediterranean Basin. The chronologies show strong correlations with summer temperature and precipitation as well as summer cloud coverage. A summer temperature reconstruction (AD 1448–2008) reveals that the Little Ice Age was characterized by low, but not extremely low temperatures on Corsica. Relatively warm temperatures during the Maunder minimum may indicate a decoupling from climate cooling registered in northern latitudes. A comparison of the summer temperature reconstruction with a summer cloud coverage reconstruction indicates warm summers with reduced cloudiness during the periods AD 1480–1520 and 1950–2008 and cool and cloudy summers during AD 1580–1620 and 1820–1890. The distinct features of the reconstruction underline the uniqueness of the Corsican climate and highlight the necessity of a better temporal and spatial resolution of climate reconstructions for a more robust estimation of current climate change on a local scale.

Beschreibung: Cryogenic cave carbonate – a new tool for estimation of the Last Glacial permafrost depth of the Central Europe Climate of the Past Discussions, 8, 2145-2185, 2012 Author(s): K. Žák, D. K. Richter, M. Filippi, R. Živor, M. Deininger, A. Mangini, and D. Scholz Cryogenic cave carbonate (CCC) represents a specific type of speleothems, whose precipitation is triggered by freezing of mineralized karst water. Coarse-crystalline CCC, which formed during slow freezing of water in cave pools, is known in 20 Central European caves located in Germany, the Czech Republic, Slovakia and Poland. All these caves are situated in an area, which was glacier-free during the Weichselian. Whereas the formation of usual types of speleothems in caves of this region usually ceased during glacials, CCC precipitation was restricted to glacial periods. Since CCC represents a novel, useful paleoclimate proxy, data from Weichselian CCC occurrences in caves in Central Europe were collected, including their C and O stable isotope systematics, U-series ages and depth below the surface. When using only the CCC data from caves with limited cave ventilation, the permafrost depths of the Weichselian can be estimated to be at least 65 m in the lowlands and uplands. An isolated CCC find indicates that Weichselian permafrost penetrated to a depth of at least 285 m in the High Tatra Mts., Slovakia. A model of the formation of coarse-crystalline CCC assumes its formation especially during periods of permafrost thawing. U-series data confirm that permafrost depth changed and CCC precipitation occurred repeatedly in the studied area during Marine Isotope Stages 4, 3 and 2. One important phase of CCC formation related to permafrost thawing occurred between 40 and 21 ka BP, and the last phase of its formation was related to the final permafrost destruction between 17 and 12 ka BP.

Beschreibung: Alluvial fan dynamics in the El'gygytgyn Crater: implications for the 3.6 Ma old sediment archive Climate of the Past Discussions, 8, 2187-2222, 2012 Author(s): G. Schwamborn, G. Fedorov, N. Ostanin, L. Schirrmeister, A. Andreev, and the El'gygytgyn Scientific Party A sedimentological program has been conducted using frozen core samples from the 141.5 m long El'gygytgyn 5011-3 permafrost well. The drill site is located in sedimentary permafrost west of the lake that partly fills the El'gygytgyn Crater. The total core sequence is interpreted as strata building up a progradational alluvial fan delta. Four structurally and texturally distinct sedimentary units are identified. Unit 1 (141.5–117.0 m) is comprised of ice-cemented, matrix-supported sandy gravel and intercalated sandy layers. Sandy layers represent sediments which rained out as particles in the deeper part of the water column under highly energetic conditions. Unit 2 (117.0–24.25 m) is dominated by ice-cemented, matrix-supported sandy gravel with individual gravel layers. Most of the unit 2 diamicton is understood to result from alluvial wash and subsequent gravitational sliding of coarse-grained material on the basin slope. Unit 3 (24.25–8.5 m) has ice-cemented, matrix-supported sandy gravel that is interrupted by sand beds. These sandy beds are associated with flooding events and represent near-shore sandy shoals. Unit 4 (8.5–0.0 m) is ice-cemented, matrix-supported sandy gravel with varying ice content, mostly higher than below. It consists of slope material and creek fill deposits. The uppermost meter is the active layer into which modern soil organic matter has been incorporated. The nature of the progradational sediment transport taking place from the western and northern crater margins may be related to the complementary occurrence of frequent turbiditic layers in the central lake basin as is known from the lake sediment record. Slope processes such as gravitational sliding and sheet flooding that takes place especially during spring melt are thought to promote mass wasting into the basin. Tectonics are inferred to have initiated the fan accumulation in the first place and possibly the off-centre displacement of the crater lake.

Beschreibung: Evaluation of turbulent dissipation rate retrievals from Doppler Cloud Radar Atmospheric Measurement Techniques, 5, 1375-1385, 2012 Author(s): M. D. Shupe, I. M. Brooks, and G. Canut Turbulent dissipation rate retrievals from cloud radar Doppler velocity measurements are evaluated using independent, in situ observations in Arctic stratocumulus clouds. In situ validation data sets of dissipation rate are derived using sonic anemometer measurements from a tethered balloon and high frequency pressure variation observations from a research aircraft, both flown in proximity to stationary, ground-based radars. Modest biases are found among the data sets in particularly low- or high-turbulence regimes, but in general the radar-retrieved values correspond well with the in situ measurements. Root mean square differences are typically a factor of 4–6 relative to any given magnitude of dissipation rate. These differences are no larger than those found when comparing dissipation rates computed from tethered-balloon and meteorological tower-mounted sonic anemometer measurements made at spatial distances of a few hundred meters. Temporal lag analyses suggest that approximately half of the observed differences are due to spatial sampling considerations, such that the anticipated radar-based retrieval uncertainty is on the order of a factor of 2–3. Moreover, radar retrievals are clearly able to capture the vertical dissipation rate structure observed by the in situ sensors, while offering substantially more information on the time variability of turbulence profiles. Together these evaluations indicate that radar-based retrievals can, at a minimum, be used to determine the vertical structure of turbulence in Arctic stratocumulus clouds.

Beschreibung: Palynological evidence for gradual vegetation and climate changes during the "African Humid Period" termination at 13° N from a Mega-Lake Chad sedimentary sequence Climate of the Past Discussions, 8, 2321-2367, 2012 Author(s): P. G. C. Amaral, A. Vincens, J. Guiot, G. Buchet, P. Deschamps, J.-C. Doumnang, and F. Sylvestre Located at the transition between the Saharian and Sahelian zones, at the center of one of the largest endoreic basins, the Lake Chad is ideally located to record regional environmental changes that occurred in the past. However, until now, no continuous archive from Lake Chad covering the Holocene has been studied. In this paper, we present pollen data from the first Holocene sedimentary sequence collected in Lake Chad (13° N; 14° E; Sahel region). Dated between ca. 6700 and ca. 5000 cal yr BP, this record encompasses the termination of the African Humid Period (AHP). Vegetational reconstructions are based on standard analyses of the pollen diagrams and are strengthened by quantitative approaches. Potential biomes that occurred at that time around Mega-Lake Chad are reconstructed using the biomization method and mean annual precipitation is estimated using the modern analogues technique. Results show that between ca. 6700 and ca. 6050 cal yr BP, a vegetation close to humid woodland or humid savanna, including elements currently found much further southward, thrived in the vicinity and/or the extra-local environment of the Mega-Lake Chad in place of the modern steppe, dry woodland and desert vegetation observed today. At the same time, montane forest populations extended further southward on the Adamawa plateau. This vegetation distribution is supported by biome reconstructions as well as by mean annual precipitation estimates of ca. 800 (−400/+700) mm for the period. The high abundance of lowland humid pollen taxa is interpreted as the result of a northward migration of the corresponding plants during the AHP driven by more favorable climatic conditions. Our interpretation in favor of a regional vegetation response to climatic changes is supported by other pollen data from several Northwestern African records. However, we cannot rule out that an increase of Chari-Logone inputs into the Mega-Lake Chad due to variations in hydrological regime might have contributed to the higher abundance of lowland humid pollen taxa observed in the mid-Holocene sedimentary sequence. Changes in the structure and floristic composition of the vegetation towards more open and drier formations occurred after ca. 6050 cal yr BP. This is also evidenced by a decrease in mean annual precipitation estimates to approximately 600 (−230/+600) mm. This change corresponds to the onset of the AHP termination. The constant presence of lowland humid taxa until ca. 5000 cal yr BP, even if displaying a slight decrease, contemporaneous with an increase in steppic taxa, demonstrates that at ca. 5000 cal yr BP the modern vegetation was not yet established in the vicinity of Lake Chad. Our data indicate that vegetational change during this period must have occurred progressively, at least over 1000 yr, and are inconsistent with an abrupt aridification and a collapse of the vegetation cover in the East-Central Saharan and Sahelian regions at the AHP termination.

Beschreibung: CH 4 , CO, and H 2 O spectroscopy for the Sentinel-5 Precursor mission: an assessment with the Total Carbon Column Observing Network measurements Atmospheric Measurement Techniques, 5, 1387-1398, 2012 Author(s): A. Galli, A. Butz, R. A. Scheepmaker, O. Hasekamp, J. Landgraf, P. Tol, D. Wunch, N. M. Deutscher, G. C. Toon, P. O. Wennberg, D. W. T. Griffith, and I. Aben The TROPOspheric Monitoring Instrument (TROPOMI) will be part of ESA's Sentinel-5 Precursor (S5P) satellite platform scheduled for launch in 2015. TROPOMI will monitor methane and carbon monoxide concentrations in the Earth's atmosphere by measuring spectra of back-scattered sunlight in the short-wave infrared (SWIR). S5P will be the first satellite mission to rely uniquely on the spectral window at 4190–4340 cm −1 (2.3 μm) to retrieve CH 4 and CO. In this study, we investigated if the absorption features of the three relevant molecules CH 4 , CO, and H 2 O are adequately known. To this end, we retrieved total columns of CH 4 , CO, and H 2 O from absorption spectra measured by two ground-based Fourier transform spectrometers that are part of the Total Carbon Column Observing Network (TCCON). The retrieval results from the 4190–4340 cm −1 range at the TROPOMI resolution (0.45 cm −1 ) were then compared to the CH 4 results obtained from the 6000 cm −1 region, and the CO results obtained from the 4190–4340 cm −1 region at the higher TCCON resolution (0.02 cm −1 ). For TROPOMI-like settings, we were able to reproduce the CH 4 columns to an accuracy of 0.3% apart from a constant bias of 1%. The CO retrieval accuracy was, through interference, systematically influenced by the shortcomings of the CH 4 and H 2 O spectroscopy. In contrast to CH 4 , the CO column error also varied significantly with atmospheric H 2 O content. Unaddressed, this would introduce seasonal and latitudinal biases to the CO columns retrieved from TROPOMI measurements. We therefore recommend further effort from the spectroscopic community to be directed at the H 2 O and CH 4 spectroscopy in the 4190–4340 cm −1 region.

Beschreibung: Does Antarctic glaciation cool the world? Climate of the Past Discussions, 8, 2645-2693, 2012 Author(s): A. Goldner, M. Huber, and R. Caballero In this study we compare the simulated climatic impact of adding the Antarctic Ice Sheet to the "Greenhouse World" of the Eocene and removing the Antarctic Ice Sheet from the Modern world. The Modern surface temperature anomaly (Δ T ) induced by Antarctic Glaciation ranges from −1.22 to −0.18 K when CO 2 is dropped from 2240 to 560 ppm, whereas the Eocene Δ T is nearly constant at −0.3 K. We calculate the climate sensitivity parameter S [Antarctica] which is defined as the change in surface temperature (Δ T ) divided by the change in radiative forcing (Δ Q Antarctica ) imposed by prescribing the glacial properties of Antarctica. While the Δ T associated with the imposed Antarctic properties is relatively consistent across the Eocene cases, the radiative forcing is not. This leads to a wide range of S [Antarctica] , with Eocene values systematically smaller than Modern. This differing temperature response in Eocene and Modern is partially due to the smaller surface area of the imposed forcing over Antarctica in the Eocene and partially due to the presence of strong positive sea-ice feedbacks in the Modern. The system's response is further mediated by differing shortwave cloud feedbacks which are large and of opposite sign operating in Modern and Eocene configurations. A negative cloud feedback warms much of the Earth's surface as a large ice sheet is introduced in Antarctica in the Eocene, whereas in the Modern this cloud feedback is positive and acts to enhance cooling introduced by adding an ice sheet. Because of the importance of cloud feedbacks in determining the final temperature sensitivity of the Antarctic Ice Sheet our results are likely to be model dependent. Nevertheless, these model results show that the radiative forcing and feedbacks induced by the Antarctic Ice Sheet did not significantly decrease global mean surface temperature across the Eocene-Oligocene transition (EOT) and that other factors like declining atmospheric CO 2 are more important for cooling across the EOT. The results indicate that climate transitions associated with glaciation depend on the climate background state. This means that using paleoclimate proxy data by itself, from the EOT to estimate Earth System Sensitivity, into the future, is made difficult without relying on climate models and consequently these modelling estimates will have large uncertainty, largely due to low clouds.

Beschreibung: New Aura Microwave Limb Sounder observations of BrO and implications for Br y Atmospheric Measurement Techniques, 5, 1741-1751, 2012 Author(s): L. Millán, N. Livesey, W. Read, L. Froidevaux, D. Kinnison, R. Harwood, I. A. MacKenzie, and M. P. Chipperfield This paper introduces a new inversion algorithm for retrievals of stratospheric BrO from the Aura Microwave Limb Sounder. This version is based on the algorithm described by Livesey et al. (2006a) but uses a more realistic atmospheric state to constrain the retrieval. A description of the methodology and an error analysis are presented. Single daily profile precision uncertainty, when taking the ascending-descending (day-night) difference, was found to be up to 40 pptv while systematic error biases were estimated to be less than about 3 pptv. Monthly mean comparisons show broad agreement with other measurements as well as with state-of-the-art numerical models. We infer a 2005 yearly total inorganic Br y using the measured MLS BrO to be 20.3 ± 4.5 pptv, which implies a contribution from very short lived substances to the stratospheric bromine budget of 5 ± 4.5 pptv.

Beschreibung: Climate and vegetation changes around the Atlantic Ocean resulting from changes in the meridional overturning circulation during deglaciation Climate of the Past Discussions, 8, 2819-2852, 2012 Author(s): D. Handiani, A. Paul, and L. Dupont The Bølling-Allerød (BA, starting ~ 14.5 ka BP) is one of the most pronounced abrupt warming periods recorded in ice and pollen proxies. The leading explanation of the cause of this warming is a sudden increase in the rate of deepwater formation in the North Atlantic Ocean and the resulting effect on the heat transport by the Atlantic Meridional Overturning Circulation (AMOC). In this study, we used the University of Victoria (UVic) Earth System-Climate Model (ESCM) to run simulations, in which a freshwater perturbation initiated a BA-like warming period. We found that under present climate conditions, the AMOC intensified when freshwater was added to the Southern Ocean. However, under Heinrich event 1 (HE1, ~ 16 ka BP) climate conditions, the AMOC only intensified when freshwater was extracted from the North Atlantic Ocean, possibly corresponding to an increase in evaporation or a decrease in precipitation in this region. The intensified AMOC led to a warming in the North Atlantic Ocean and a cooling in the South Atlantic Ocean, resembling the bipolar seesaw pattern typical of the last glacial period. In addition to the physical response, we also studied the simulated vegetation response around the Atlantic Ocean region. Corresponding with the bipolar seesaw hypothesis, the rainbelt associated with the Intertropical Convergence Zone (ITCZ) shifted northward and affected the vegetation pattern in the tropics. The most sensitive vegetation area was found in tropical Africa, where grass cover increased and tree cover decreased under dry climate conditions. An equal but opposite response to the collapse and recovery of the AMOC implied that the change in vegetation cover was transient and robust to an abrupt climate change such as during the BA period, which is also supported by paleovegetation data. The results are in agreement with paleovegetation records from Western tropical Africa, which also show a reduction in forest cover during this time period. Further agreement between data and model results was found for the uplands of North America and Southern Europe, where grassland along with warm and dry climates were simulated. However, our model simulated vegetation changes in South and North America that were much smaller than reconstructed. Along the west and east coast of North America we simulated drier vegetation than the pollen records suggest.

Beschreibung: Multi-wavelength Raman lidar, sun photometric and aircraft measurements in combination with inversion models for the estimation of the aerosol optical and physico-chemical properties over Athens, Greece Atmospheric Measurement Techniques, 5, 1793-1808, 2012 Author(s): R. E. Mamouri, A. Papayannis, V. Amiridis, D. Müller, P. Kokkalis, S. Rapsomanikis, E. T. Karageorgos, G. Tsaknakis, A. Nenes, S. Kazadzis, and E. Remoundaki A novel procedure has been developed to retrieve, simultaneously, the optical, microphysical and chemical properties of tropospheric aerosols with a multi-wavelength Raman lidar system in the troposphere over an urban site (Athens, Greece: 37.9° N, 23.6° E, 200 m a.s.l.) using data obtained during the European Space Agency (ESA) THERMOPOLIS project, which took place between 15–31 July 2009 over the Greater Athens Area (GAA). We selected to apply our procedure for a case study of intense aerosol layers that occurred on 20–21 July 2009. The National Technical University of Athens (NTUA) EOLE 6-wavelength Raman lidar system has been used to provide the vertical profiles of the optical properties of aerosols (extinction and backscatter coefficients, lidar ratio) and the water vapor mixing ratio. An inversion algorithm was used to derive the mean aerosol microphysical properties (mean effective radius ( r eff ), single-scattering albedo ω ) and mean complex refractive index ( m )) at selected heights in the 2–3 km height region. We found that r eff was 0.14–0.4 (±0.14) μm, ω was 0.63–0.88 (±0.08) (at 532 nm) and m ranged from 1.44 (±0.10) + 0.01 (±0.01) i to 1.55 (±0.12) + 0.06 (±0.02) i , in good agreement (only for the r eff values) with in situ aircraft measurements. The water vapor and temperature profiles were incorporated into the ISORROPIA II model to propose a possible in situ aerosol composition consistent with the retrieved m and ω values. The retrieved aerosol chemical composition in the 2–3 km height region gave a variable range of sulfate (0–60%) and organic carbon (OC) content (0–50%), although the OC content increased (up to 50%) and the sulfate content dropped (up to 30%) around 3 km height; the retrieved low ω value (0.63), indicates the presence of absorbing biomass burning smoke mixed with urban haze. Finally, the retrieved aerosol microphysical properties were compared with column-integrated sun photometer CIMEL data.

Beschreibung: The RAMNI airborne lidar for cloud and aerosol research Atmospheric Measurement Techniques, 5, 1779-1792, 2012 Author(s): F. Cairo, G. Di Donfrancesco, L. Di Liberto, and M. Viterbini We describe an airborne lidar for the characterization of atmospheric aerosol. The system has been set up in response to the need to monitor extended regions where the air traffic may be posed at risk by the presence of potentially harmful volcanic ash, and to study the characteristics of volcanic emissions both near the source region and when transported over large distances. The lidar provides backscatter and linear depolarization profiles at 532 nm, from which aerosol and cloud properties can be derived. The paper presents the characteristics and capabilities of the lidar system and gives examples of its airborne deployment. Observations from three flights, aimed at assessing the system capabilities in unperturbed atmospheric conditions, and at characterizing the emissions near a volcanic ash source (Mt. Etna) and transported far away from the source, are presented and discussed.

Beschreibung: Past climate changes and permafrost depth at the Lake El'gygytgyn site: implications from data and thermal modelling Climate of the Past Discussions, 8, 2607-2644, 2012 Author(s): D. Mottaghy, G. Schwamborn, and V. Rath We present results of numerical simulations of the temperature field of the subsurface around and beneath the crater Lake El'gygytgyn in NE Russia, which is subject of an interdisciplinary drilling campaign within the International Continental Drilling Program (ICDP). This study focuses on determining the permafrost depth and the transition between talik and permafrost regimes, both, under steady-state and transient conditions of past climate changes. Thermal properties of the subsurface are deduced from measurements on three representative core samples taken from the quaternary sediments and the underlying impact rock. Further information is derived from the available geophysical logs and literature data. The temperature data from the lake borehole ICDP site 5011-1 down to 400 m depth below lake bottom are dominated by thermal perturbations related to the drilling process, and thus only give reliable values for the lowermost value in the borehole. Undisturbed temperature data recorded over more than two years in the 140 m deep land-based borehole ICDP site 5011-3 allow to determine the mean annual ground surface temperature (GST), as well as its history (GSTH) to a certain extent. Although the borehole's depth is by far not sufficient for a complete reconstruction of past temperatures back to the last glacial maximum (LGM), the temperature data and our modelling results show that there is still an influence of the LGM on the thermal regime, and thus on the permafrost depth. Whereas the latter result is obtained from the deeper part of the temperature profile, the rather strong curvature of the temperature data in shallower depths around 30 m can be explained by a comparatively large amplitude of the Little Ice Age (LIA), with a subsequently persistent cool period. Other mechanisms like varying porosity may also have an influence on the temperature profile, however, our modelling studies imply a major contribution from recent climate changes.

Beschreibung: Duration of Greenland Stadial 22 and ice-gas Δage from counting of annual layers in Greenland NGRIP ice core Climate of the Past Discussions, 8, 2583-2605, 2012 Author(s): P. Vallelonga, G. Bertagna, T. Blunier, H. A. Kjær, T. J. Popp, S. O. Rasmussen, J. P. Steffensen, C. Stowasser, A. S. Svensson, E. Warming, M. Winstrup, M. Bigler, and S. Kipfstuhl The NorthGRIP ice core chronology GICC05modelext is composed of the annual-layer counted GICC05 chronology to 60 kyr before 2000 AD (b2k), and an ice flow model dating the deepest part of the ice core to 123 kyr b2k. Determination of annual strata in ice beyond 60 kyr b2k has been challenged by the thinning of annual layers to

Beschreibung: Characterization of atmospheric aerosol in the US Southeast from ground- and space-based measurements over the past decade Atmospheric Measurement Techniques, 5, 1667-1682, 2012 Author(s): E. J. Alston, I. N. Sokolik, and O. V. Kalashnikova This study examines how aerosols measured from the ground and space over the US Southeast change temporally over a regional scale during the past decade. PM 2.5 (particulate matter with aerodynamic diameter 〉2.5 micrometers) data consist of two datasets that represent the measurements that are used for regulatory purposes by the US EPA (Environmental Protection Agency) and continuous measurements used for quickly disseminating air quality information. AOD (aerosol optical depth) data come from three NASA sensors: the MODIS sensors onboard Terra and Aqua satellites and the MISR sensor onboard the Terra satellite. We analyze all available data over the state of Georgia from 2000–2009 of both types of aerosol data. The analysis reveals that during the summer the large metropolitan area of Atlanta has average PM 2.5 concentrations that are 50% more than the remainder of the state. Strong seasonality is detected in both the AOD and PM 2.5 datasets, as evidenced by a threefold increase of AOD from mean winter values to mean summer values, and the increase in PM 2.5 concentrations is almost twofold over the same period. Additionally, there is agreement between MODIS and MISR onboard the Terra satellite during the spring and summer, having correlation coefficients of 0.64 and 0.71, respectively. Monthly anomalies were used to determine the presence of a trend in all considered aerosol datasets. We found negative linear trends for both the monthly AOD anomalies from MODIS onboard Terra and the PM 2.5 datasets, which are statistically significant. Decreasing trends were also found for MISR onboard Terra and MODIS onboard Aqua, but those trends were not statistically significant. The observed decrease in AOD and PM 2.5 concentrations may be indicative of the brightening over the study region during the past decade.

Beschreibung: Eddy-covariance flux measurements with a weight-shift microlight aircraft Atmospheric Measurement Techniques, 5, 1699-1717, 2012 Author(s): S. Metzger, W. Junkermann, M. Mauder, F. Beyrich, K. Butterbach-Bahl, H. P. Schmid, and T. Foken The objective of this study is to assess the feasibility and quality of eddy-covariance flux measurements from a weight-shift microlight aircraft (WSMA). Firstly, we investigate the precision of the wind measurement (σ u,v ≤ 0.09 m s −1 , σ w = 0.04 m s −1 ), the lynchpin of flux calculations from aircraft. From here, the smallest resolvable changes in friction velocity (0.02 m s −1 ), and sensible- (5 W m −2 ) and latent (3 W m −2 ) heat flux are estimated. Secondly, a seven-day flight campaign was performed near Lindenberg (Germany). Here we compare measurements of wind, temperature, humidity and respective fluxes between a tall tower and the WSMA. The maximum likelihood functional relationship (MLFR) between tower and WSMA measurements considers the random error in the data, and shows very good agreement of the scalar averages. The MLFRs for standard deviations (SDs, 2–34%) and fluxes (17–21%) indicate higher estimates of the airborne measurements compared to the tower. Considering the 99.5% confidence intervals, the observed differences are not significant, with exception of the temperature SD. The comparison with a large-aperture scintillometer reveals lower sensible heat flux estimates at both tower (−40 to −25%) and WSMA (−25–0%). We relate the observed differences to (i) inconsistencies in the temperature and wind measurement at the tower and (ii) the measurement platforms' differing abilities to capture contributions from non-propagating eddies. These findings encourage the use of WSMA as a low cost and highly versatile flux measurement platform.

Beschreibung: Global and regional evaluation of over-land spectral aerosol optical depth retrievals from SeaWiFS Atmospheric Measurement Techniques, 5, 1761-1778, 2012 Author(s): A. M. Sayer, N. C. Hsu, C. Bettenhausen, M.-J. Jeong, B. N. Holben, and J. Zhang This study evaluates a new spectral aerosol optical depth (AOD) dataset derived from Sea-viewing Wide Field-of-view Sensor (SeaWiFS) measurements over land. First, the data are validated against Aerosol Robotic Network (AERONET) direct-sun AOD measurements and found to compare well on a global basis. If only data with the highest quality flag are used, the correlation is 0.86 and 72% of matchups fall within an expected absolute uncertainty of 0.05 + 20% (for the wavelength of 550 nm). The quality is similar at other wavelengths and stable over the 13-yr (1997–2010) mission length. Performance tends to be better over vegetated, low-lying terrain with typical AOD of 0.3 or less, such as found over much of North America and Eurasia. Performance tends to be poorer for low-AOD conditions near backscattering geometries, where SeaWiFS overestimates AOD, or optically-thick cases of absorbing aerosol, where SeaWiFS tends to underestimate AOD. Second, the SeaWiFS data are compared with midvisible AOD derived from the Moderate Resolution Imaging Spectrometer (MODIS) and Multiangle Imaging Spectroradiometer (MISR). All instruments show similar spatial and seasonal distributions of AOD, although there are regional and seasonal offsets between them. At locations where AERONET data are available, these offsets are largely consistent with the known validation characteristics of each dataset. With the results of this study in mind, the SeaWiFS over-land AOD record is suitable for quantitative scientific use.

Beschreibung: Critical surface albedo and its implications to aerosol remote sensing Atmospheric Measurement Techniques, 5, 1653-1665, 2012 Author(s): F. C. Seidel and C. Popp We analyse the critical surface albedo (CSA) and its implications to aerosol remote sensing. CSA is defined as the surface albedo where the reflectance at top-of-atmosphere (TOA) does not depend on aerosol optical depth (AOD). AOD retrievals are therefore inaccurate at the CSA. The CSA is obtained by derivatives of the TOA reflectance with respect to AOD using a radiative transfer code. We present the CSA and the effect of surface albedo uncertainties on AOD retrieval and atmospheric correction as a function of aerosol single-scattering albedo, illumination and observation geometry, wavelength and AOD. In general, increasing aerosol absorption and increasing scattering angles lead to lower CSA. In contrast to the strict definition of the CSA, we show that the CSA can also slightly depend on AOD and therefore rather represent a small range of surface albedo values. This was often neglected in previous studies. The following implications to aerosol remote sensing applications were found: (i) surface albedo uncertainties result in large AOD retrieval errors, particularly close to the CSA; (ii) AOD retrievals of weakly or non-absorbing aerosols require dark surfaces, while strongly absorbing aerosols can be retrieved more accurately over bright surfaces; (iii) the CSA may help to estimate aerosol absorption; and (iv) the presented sensitivity of the reflectance at TOA to AOD provides error estimations to optimise AOD retrieval algorithms.

Beschreibung: Assessment of two aerosol optical thickness retrieval algorithms applied to MODIS Aqua and Terra measurements in Europe Atmospheric Measurement Techniques, 5, 1727-1740, 2012 Author(s): P. Glantz and M. Tesche The aim of the present study is to validate AOT (aerosol optical thickness) and Ångström exponent (α), obtained from MODIS (MODerate resolution Imaging Spectroradiometer) Aqua and Terra calibrated level 1 data (1 km horizontal resolution at ground) with the SAER (Satellite AErosol Retrieval) algorithm and with MODIS Collection 5 (c005) standard product retrievals (10 km horizontal resolution), against AERONET (AErosol RObotic NETwork) sun photometer observations over land surfaces in Europe. An inter-comparison of AOT at 0.469 nm obtained with the two algorithms has also been performed. The time periods investigated were chosen to enable a validation of the findings of the two algorithms for a maximal possible variation in sun elevation. The satellite retrievals were also performed with a significant variation in the satellite-viewing geometry, since Aqua and Terra passed the investigation area twice a day for several of the cases analyzed. The validation with AERONET shows that the AOT at 0.469 and 0.555 nm obtained with MODIS c005 is within the expected uncertainty of one standard deviation of the MODIS c005 retrievals (ΔAOT = ± 0.05 ± 0.15 · AOT). The AOT at 0.443 nm retrieved with SAER, but with a much finer spatial resolution, also agreed reasonably well with AERONET measurements. The majority of the SAER AOT values are within the MODIS c005 expected uncertainty range, although somewhat larger average absolute deviation occurs compared to the results obtained with the MODIS c005 algorithm. The discrepancy between AOT from SAER and AERONET is, however, substantially larger for the wavelength 488 nm. This means that the values are, to a larger extent, outside of the expected MODIS uncertainty range. In addition, both satellite retrieval algorithms are unable to estimate α accurately, although the MODIS c005 algorithm performs better. Based on the inter-comparison of the SAER and MODIS c005 algorithms, it was found that SAER on the whole is able to obtain results within the expected uncertainty range of MODIS Aqua and Terra observations.

Beschreibung: On-line determination of ammonia at low pptv mixing ratios in the CLOUD chamber Atmospheric Measurement Techniques, 5, 1719-1725, 2012 Author(s): F. Bianchi, J. Dommen, S. Mathot, and U. Baltensperger A new instrument for the on-line determination of ammonia was developed. Since ammonia is a rather sticky compound, sampling losses were minimised with a new sampling device where the ammonia was transferred to the liquid phase only 5 mm after the inlet tip. The liquid phase was then analyzed by long pathlength absorption spectrophotometry using the Berthelot reaction with phenol and hypochlorite as reagents. The measurements were made during the CLOUD3 campaign at CERN where the influence of ammonia on the nucleation rate was studied. At stable conditions the detection limit reached with this instrument was 35 pptv (air flow rate of 2 l min −1 , liquid flow rate of 0.3 ml min −1 ), although occasionally the instrument was affected by background problems. The range of mixing ratios during this campaign was varied from the background contamination (

Beschreibung: Simulated oxygen isotopes in cave drip water and speleothem calcite in European caves Climate of the Past Discussions, 8, 2777-2817, 2012 Author(s): A. Wackerbarth, P. M. Langebroek, M. Werner, G. Lohmann, S. Riechelmann, and A. Mangini Interpreting stable oxygen isotope (δ 18 O) records from stalagmites is still one of the complex tasks in speleothem research. Here, we present a novel model-based approach, where we force a model describing the processes and modifications of δ 18 O from rain water to speleothem calcite (Oxygen isotope Drip water and Stalagmite Model – ODSM) with the results of a state-of-the-art atmospheric general circulation model enhanced by explicit isotope diagnostics (ECHAM5-wiso). The approach is neither climate nor cave-specific and allows an integrated assessment of the influence of different varying climate variables, e.g. temperature and precipitation amount, on the isotopic composition of drip water and speleothem calcite. First, we apply and evaluate this new approach under present-day climate conditions using observational data from seven caves from different geographical regions in Europe. Each of these caves provides measured δ 18 O values of drip water and speleothem calcite to which we compare our simulated isotope values. For six of the seven caves modeled δ 18 O values of drip water and speleothem calcite are in good agreement with observed values. The mismatch of the remaining cave might be caused by the complexity of the cave system, beyond the parameterizations included in our cave model. We then examine the response of the cave system to mid-Holocene (6000 yr before present, 6 ka) climate conditions by forcing the ODSM with ECHAM5-wiso results from 6 ka simulations. For a set of twelve European caves, we compare the modeled mid-Holocene-to-modern difference in speleothem calcite δ 18 O to available measurements. We show that the general European changes are simulated well. However, local discrepancies are found, and might be explained either by a too low model resolution, complex local soil-atmosphere interactions affecting evapotranspiration or by cave specific factors such as non-equilibrium fractionation processes.

Beschreibung: Dimethylamine and ammonia measurements with ion chromatography during the CLOUD4 campaign Atmospheric Measurement Techniques, 5, 2161-2167, 2012 Author(s): A. P. Praplan, F. Bianchi, J. Dommen, and U. Baltensperger The CLOUD project investigates the influence of galactic cosmic rays on the nucleation of new particles in an environmental chamber at CERN. Dimethylamine (DMA) was injected intentionally into the CLOUD chamber to reach atmospherically relevant levels away from sources (up to 100 pptv) in order to study its effect on nucleation with sulphuric acid and water at 278 K. Quantification of DMA and also background ammonia (NH 3 ) was performed with ion chromatography (IC). The IC method used together with the sampling line developed for CLOUD in order to measure NH 3 and DMA at low pptv levels is described; the overall sampling efficiency of the method is discussed; and, finally, mixing ratios of NH 3 and DMA measured during CLOUD4 are reported.

Beschreibung: Geophysical validation and long-term consistency between GOME-2/MetOp-A total ozone column and measurements from the sensors GOME/ERS-2, SCIAMACHY/ENVISAT and OMI/Aura Atmospheric Measurement Techniques, 5, 2169-2181, 2012 Author(s): M. E. Koukouli, D. S. Balis, D. Loyola, P. Valks, W. Zimmer, N. Hao, J.-C. Lambert, M. Van Roozendael, C. Lerot, and R. J. D. Spurr The main aim of the paper is to assess the consistency of five years of Global Ozone Monitoring Experiment-2/Metop-A [GOME-2] total ozone columns and the long-term total ozone satellite monitoring database already in existence through an extensive inter-comparison and validation exercise using as reference Brewer and Dobson ground-based measurements. The behaviour of the GOME-2 measurements is being weighed against that of GOME (1995–2011), Ozone Monitoring Experiment [OMI] (since 2004) and the Scanning Imaging Absorption spectroMeter for Atmospheric CartograpHY [SCIAMACHY] (since 2002) total ozone column products. Over the background truth of the ground-based measurements, the total ozone columns are inter-evaluated using a suite of established validation techniques; the GOME-2 time series follow the same patterns as those observed by the other satellite sensors. In particular, on average, GOME-2 data underestimate GOME data by about 0.80%, and underestimate SCIAMACHY data by 0.37% with no seasonal dependence of the differences between GOME-2, GOME and SCIAMACHY. The latter is expected since the three datasets are based on similar DOAS algorithms. This underestimation of GOME-2 is within the uncertainty of the reference data used in the comparisons. Compared to the OMI sensor, on average GOME-2 data underestimate OMI_DOAS (collection 3) data by 1.28%, without any significant seasonal dependence of the differences between them. The lack of seasonality might be expected since both the GOME data processor [GDP] 4.4 and OMI_DOAS are DOAS-type algorithms and both consider the variability of the stratospheric temperatures in their retrievals. Compared to the OMI_TOMS (collection 3) data, no bias was found. We hence conclude that the GOME-2 total ozone columns are well suitable to continue the long-term global total ozone record with the accuracy needed for climate monitoring studies.

Beschreibung: Multi-periodic climate dynamics: spectral analysis of long-term instrumental and proxy temperature records Climate of the Past Discussions, 8, 4493-4511, 2012 Author(s): H.-J. Lüdecke, A. Hempelmann, and C. O. Weiss The longest six instrumental temperature records of monthly means reach back maximally to 1757 AD and were recorded in Europe. All six show a V-shape, with temperature drop in the 19th and rise in the 20th century. Proxy temperature time series of Antarctic ice cores show this same characteristic shape, indicating this pattern as a global phenomenon. We used the mean of the 6 instrumental records for analysis by discrete Fourier transformation (DFT), wavelets, and the detrended fluctuation method (DFA). For comparison, a stalagmite record was also analyzed by DFT. The harmonic decomposition of the mean shows only 6 significant frequencies above periods over 30 yr. The Pearson correlation between the mean, smoothed by a 15 yr running average (boxcar) and the reconstruction using the 6 significant frequencies yields r = 0.961. This good agreement has a 〉 99.9% confidence level confirmed by Monte Carlo simulations. Assumption of additional forcing by anthropogenic green house gases would therefore not improve the agreement between measurement and temperature construction from the 6 documented periodicities. We find indications that the observed periodicities result from intrinsic system dynamics.

Beschreibung: Tephrostratigraphic studies on a sediment core from Lake Prespa in the Balkans Climate of the Past Discussions, 8, 4443-4492, 2012 Author(s): M. Damaschke, R. Sulpizio, G. Zanchetta, B. Wagner, A. Böhm, N. Nowaczyk, J. Rethemeyer, and A. Hilgers A detailed tephrostratigraphic record, which dates back to Marine Isotope Stage (MIS) 5, has been established from a 17.76 m long core (Co1215) from Lake Prespa (Macedonia, Albania and Greece). A total of eleven tephra and cryptotephra layers (PT0915-1 to PT0915-11) were identified, using XRF scanning, magnetic susceptibility measurements, and macro- and microscopic inspection of the sediments. The major element composition of glass shards and/or micro-pumice fragments indicates that the tephras and cryptotephras originate from the explosive volcanism of Italy. Eight tephra and cryptotephra layers were correlated with specific volcanic eruptions: cryptotephra PT0915-1 with the 512 AD eruption of Somma-Vesuvius (1438 cal yr BP), tephra PT0915-2 with the Mercato eruption of Somma-Vesuvius (8890 ± 90 cal yr BP), cryptotephras PT0915-3 and PT0915-4 with Tufi Biancastri/LN1-LN2 of the Campi Flegrei (14 749 ± 523 cal yr BP and 15 551 ± 621 cal yr BP), tephra PT0915-5 with the SMP1-e/Y-3 eruption of the Campi Flegrei (30 000–31 000 cal yr BP), tephra PT0915-7 with the Campanian Ignimbrite/Y-5 of the Campi Flegrei (39 280 ± 110 cal yr BP), cryptotephra PT0915-8 with the SMP1-a event of Ischia Island (around 44 000 cal yr BP) and tephra PT0915-9 with the Green Tuff/Y-6 eruption of Pantelleria Island (around 45 000 cal yr BP). Tephra PT0915-11 could be attributed to the volcanic activity of Mount Etna, but probably represents a hitherto unknown eruption at ca. 60 000 cal yr BP. Cryptotephras PT0915-6 and PT0915-10 remain unclassified so far, but according to the presented age-depth model these would have been deposited around 35 000 and 48 500 cal yr BP, respectively. Some of the tephras and cryptotephras are recognised for the first time in the Balkan region. The tephrostratigraphic work provides important information about ash dispersal and explosion patterns of source volcanoes and can be used to correlate and date geographically distant paleoenvironmental and archaeological archives in the central Mediterranean region. Moreover, the tephrostratigraphic work in combination with radiocarbon and electron spin resonance (ESR) dating is a precondition for paleoclimatic reconstructions inferred from the sediment succession Co1215.

Beschreibung: Polarimetric X-band weather radar measurements in the tropics: radome and rain attenuation correction Atmospheric Measurement Techniques, 5, 2183-2199, 2012 Author(s): M. Schneebeli, J. Sakuragi, T. Biscaro, C. F. Angelis, I. Carvalho da Costa, C. Morales, L. Baldini, and L. A. T. Machado A polarimetric X-band radar has been deployed during one month (April 2011) for a field campaign in Fortaleza, Brazil, together with three additional laser disdrometers. The disdrometers are capable of measuring the raindrop size distributions (DSDs), hence making it possible to forward-model theoretical polarimetric X-band radar observables at the point where the instruments are located. This set-up allows to thoroughly test the accuracy of the X-band radar measurements as well as the algorithms that are used to correct the radar data for radome and rain attenuation. For the campaign in Fortaleza it was found that radome attenuation dominantly affects the measurements. With an algorithm that is based on the self-consistency of the polarimetric observables, the radome induced reflectivity offset was estimated. Offset corrected measurements were then further corrected for rain attenuation with two different schemes. The performance of the post-processing steps was analyzed by comparing the data with disdrometer-inferred polarimetric variables that were measured at a distance of 20 km from the radar. Radome attenuation reached values up to 14 dB which was found to be consistent with an empirical radome attenuation vs. rain intensity relation that was previously developed for the same radar type. In contrast to previous work, our results suggest that radome attenuation should be estimated individually for every view direction of the radar in order to obtain homogenous reflectivity fields.

Beschreibung: Modulation of Late Cretaceous and Cenozoic climate by variable drawdown of atmospheric p CO 2 from weathering of basaltic provinces on continents drifting through the equatorial humid belt Climate of the Past Discussions, 8, 4513-4564, 2012 Author(s): D. V. Kent and G. Muttoni The small reservoir of carbon dioxide in the atmosphere ( p CO 2 ) that modulates climate through the greenhouse effect reflects a delicate balance between large fluxes of sources and sinks. The major long-term source of CO 2 is global outgassing from sea-floor spreading, subduction, hotspot activity, and metamorphism; the ultimate sink is through weathering of continental silicates and deposition of carbonates. Most carbon cycle models are driven by changes in the source flux scaled to variable rates of ocean floor production. However, ocean floor production may not be distinguishable from being steady since 180 Ma. We evaluate potential changes in sources and sinks of CO 2 for the past 120 Ma in a paleogeographic context. Our new calculations show that although decarbonation of pelagic sediments in Tethyan subduction likely contributed to generally high p CO 2 levels from the Late Cretaceous until the Early Eocene, shutdown of Tethyan subduction with collision of India and Asia at the Early Eocene Climate Optimum at around 50 Ma was inadequate to account for the large and prolonged decrease in p CO 2 that eventually allowed the growth of significant Antarctic ice sheets by around 34 Ma. Instead, variation in area of continental basaltic provinces in the equatorial humid belt (5° S–5° N) seems to be the dominant control on how much CO 2 is retained in the atmosphere via the silicate weathering feedback. The arrival of the highly weatherable Deccan Traps in the equatorial humid belt at around 50 Ma was decisive in initiating the long-term slide to lower atmospheric p CO 2 , which was pushed further down by the emplacement of the 30 Ma Ethiopian Traps near the equator and the southerly tectonic extrusion of SE Asia, an arc terrane that presently is estimated to account for 1/4 of CO 2 consumption from all basaltic provinces that account for ~1/3 of the total CO 2 consumption by continental silicate weathering (Dessert et al., 2003). A negative climate-feedback mechanism that (usually) inhibits the complete collapse of atmospheric p CO 2 is the accelerating formation of thick cation-deficient soils that retard chemical weathering of the underlying bedrock. Nevertheless, equatorial climate seems to be relatively insensitive to p CO 2 greenhouse forcing and thus with availability of some rejuvenating relief as in arc terranes or thick basaltic provinces, silicate weathering in this venue is not subject to a strong negative feedback, providing an avenue for sporadic ice ages. The safety valve that prevents excessive atmospheric p CO 2 levels is the triggering of silicate weathering of continental areas and basaltic provinces in the temperate humid belt. Increase in Mg/Ca ratio of seawater over the Cenozoic may be due to weathering input from continental basaltic provinces.

Beschreibung: Long term January–March and May–August temperature reconstructions from tree-ring records from Bosnia and Herzegovina Climate of the Past Discussions, 8, 4401-4442, 2012 Author(s): S. Poljanšek, A. Ceglar, and T. Levanič We present the first spring and summer temperature reconstruction for the north-western part of the Balkan Peninsula. The reconstruction is based on tree-ring width measurements from 7 representative black pine ( Pinus nigra Arnold) sites in Bosnia and Herzegovina (BiH). We found a significant, positive influence of above-average January–March temperatures on 4 sites (Blace, Peručica, Šator, Konjuh) and a negative influence of above-average May–August temperatures and a positive relationship with an above-average sum of May–August precipitation on tree-ring width formation from 3 sites (Krivaja, Prusac, Šipovo). A 31-yr running correlation between temperature and precipitation of the May–August period and tree-ring indices gave a stable relationship between 1901 and the 1960s, after which values of correlation coefficients decrease to the level of significance. A change in summer cyclones in the central part of the Adriatic Sea is presented as a possible cause of the divergence with the climate signal. In the period of calibration and verification of the linear model for the group of 3 sites (Krivaja, Prusac, Šipovo), the best relationship was found between tree-ring indices and mean May–August temperatures of the current year. For the group of 4 sites (Blace, Peručica, Šator, Konjuh), the relationship between tree-ring indices and mean January–March temperatures of the current year is the strongest. The developed models were used for reconstruction of May–August temperatures for BiH for the period 1701–1901 and January–March temperatures for the period 1685–1901. Using the method of percentiles (85th and 15th) we identified extreme hot/cool summers and warm/cold springs and compared them to available documentary historical sources and other reconstructions from the broader region.

Beschreibung: A compact, fast UV photometer for measurement of ozone from research aircraft Atmospheric Measurement Techniques, 5, 2201-2210, 2012 Author(s): R. S. Gao, J. Ballard, L. A. Watts, T. D. Thornberry, S. J. Ciciora, R. J. McLaughlin, and D. W. Fahey In situ measurements of atmospheric ozone (O 3 ) are performed routinely from many research aircraft platforms. The most common technique depends on the strong absorption of ultraviolet (UV) light by ozone. As atmospheric science advances to the widespread use of unmanned aircraft systems (UASs), there is an increasing requirement for minimizing instrument space, weight, and power while maintaining instrument accuracy, precision and time response. The design and use of a new, dual-beam, UV photometer instrument for in situ O 3 measurements is described. A polarization optical-isolator configuration is utilized to fold the UV beam inside the absorption cells, yielding a 60-cm absorption length with a 30-cm cell. The instrument has a fast sampling rate (2 Hz at

Beschreibung: High-resolution NO 2 remote sensing from the Airborne Prism EXperiment (APEX) imaging spectrometer Atmospheric Measurement Techniques, 5, 2211-2225, 2012 Author(s): C. Popp, D. Brunner, A. Damm, M. Van Roozendael, C. Fayt, and B. Buchmann We present and evaluate the retrieval of high spatial resolution maps of NO 2 vertical column densities (VCD) from the Airborne Prism EXperiment (APEX) imaging spectrometer. APEX is a novel instrument providing airborne measurements of unique spectral and spatial resolution and coverage as well as high signal stability. In this study, we use spectrometer data acquired over Zurich, Switzerland, in the morning and late afternoon during a flight campaign on a cloud-free summer day in June 2010. NO 2 VCD are derived with a two-step approach usually applied to satellite NO 2 retrievals, i.e. a DOAS analysis followed by air mass factor calculations based on radiative transfer computations. Our analysis demonstrates that APEX is clearly sensitive to NO 2 VCD above typical European tropospheric background abundances (〉1 × 10 15 molec cm −2 ). The two-dimensional maps of NO 2 VCD reveal a very convincing spatial distribution with strong gradients around major NO x sources (e.g. Zurich airport, waste incinerator, motorways) and low NO 2 in remote areas. The morning overflights resulted in generally higher NO 2 VCD and a more distinct pattern than the afternoon overflights which can be attributed to the meteorological conditions prevailing during that day with stronger winds and hence larger dilution in the afternoon. The remotely sensed NO 2 VCD are also in reasonably good agreement with ground-based in-situ measurements from air quality networks considering the limitations of comparing column integrals with point measurements. Airborne NO 2 remote sensing using APEX will be valuable to detect NO 2 emission sources, to provide input for NO 2 emission modelling, and to establish links between in-situ measurements, air quality models, and satellite NO 2 products.

Beschreibung: Proxy benchmarks for intercomparison of 8.2 ka simulations Climate of the Past Discussions, 8, 3765-3789, 2012 Author(s): C. Morrill, D. M. Anderson, B. A. Bauer, R. Buckner, E. P. Gille, W. S. Gross, M. Hartman, and A. Shah The Paleoclimate Modelling Intercomparison Project (PMIP3) now includes the 8.2 ka event as a test of model sensitivity to North Atlantic freshwater forcing. To provide benchmarks for intercomparison, we compiled and analyzed high-resolution records spanning this event. Two previously-described anomaly patterns that emerge are cooling around the North Atlantic and drier conditions in the Northern Hemisphere tropics. Newer to this compilation are more robustly-defined wetter conditions in the Southern Hemisphere tropics and regionally-limited warming in the Southern Hemisphere. Most anomalies around the globe lasted on the order of 100 to 150 yr. More quantitative reconstructions are now available and indicate cooling of 1.0 to 1.2 °C and a ~20% decrease in precipitation in parts of Europe, as well as spatial gradients in δ 18 O from the high to low latitudes. Unresolved questions remain about the seasonality of the climate response to freshwater forcing and the extent to which the bipolar seesaw operated in the early Holocene.