ALBERT

Description: The ongoing disintegration of large ice shelf parts in Antarctica raise the need for a better understanding of the physical processes that trigger critical crack growth in ice shelves. Finite elements in combination with configurational forces facilitate the analysis of single surface fractures in ice under various boundary conditions and material parameters. The principles of linear elastic fracture mechanics are applied to show the strong influence of different depth dependent functions for the density and the Young’s modulus on the stress intensity factor KI at the crack tip. Ice, for this purpose, is treated as an elastically compressible solid and the conse- quences of this choice in comparison to the predominant in- compressible approaches are discussed. The computed stress intensity factors KI for dry and water filled cracks are com- pared to critical values KIc from measurements that can be found in literature.

Description: Permafrost is one of the essential climate variables addressed by the Global Terrestrial Observing System (GCOS). Remote sensing data provide area-wide monitoring of e.g. surface temperatures or soil surface status (frozen or thawed state) in the Arctic and Subarctic, where ground data collection is difficult and restricted to local measurements at few monitoring sites. The task of the ESA Data User Element (DUE) Permafrost project is to build-up an Earth observation service for northern high-latitudinal permafrost applications with extensive involvement of the international permafrost research community (www.ipf.tuwien.ac.at/permafrost). The satellite-derived DUE Permafrost products are Land Surface Temperature, Surface Soil Moisture, Surface Frozen and Thawed State, Digital Elevation Model (locally as remote sensing product and circumpolar as non-remote sensing product) and Subsidence, and Land Cover. Land Surface Temperature, Surface Soil Moisture, and Surface Frozen and Thawed State will be provided for the circumpolar permafrost area north of 55° N with 25 km spatial resolution. In addition, regional products with higher spatial resolution were developed for five case study regions in different permafrost zones of the tundra and taiga (Laptev Sea [RU], Central Yakutia [RU], Western Siberia [RU], Alaska N-S transect, [US] Mackenzie River and Valley [CA]). This study shows the evaluation of two DUE Permafrost regional products, Land Surface Temperature and Surface Frozen and Thawed State, using freely available ground truth data from the Global Terrestrial Network of Permafrost (GTN-P) and monitoring data from the Russian-German Samoylov research station in the Lena River Delta (Central Siberia, RU). The GTN-P permafrost monitoring sites with their position in different permafrost zones are highly qualified for the validation of DUE Permafrost remote sensing products. Air and surface temperatures with high-temporal resolution from eleven GTN-P sites in Alaska and four sites in Siberia were used to match up LST products. Daily average GTN-P borehole- and air temperature data for three Alaskan and six Western Siberian sites were used to evaluate surface frozen and thawed. First results are promising and demonstrate the great benefit of freely available ground truth databases for remote sensing products.

Description: Here we present results of the first comprehensive study of sulphur compounds and methane in the oligotrophic tropical West Pacific Ocean. The concentrations of dimethylsuphide (DMS), dimethylsulphoniopropionate (DMSP), dimethylsulphoxide (DMSO), and methane (CH4), as well as various phytoplankton marker pigments in the surface ocean were measured along a north-south transit from Japan to Australia in October 2009. DMS (0.9 nmol l−1), dissolved DMSP (DMSPd, 1.6 nmol l−1) and particulate DMSP (DMSPp, 2 nmol l−1) concentrations were generally low, while dissolved DMSO (DMSOd, 4.4 nmol l−1) and particulate DMSO (DMSOp, 11.5 nmol l−1) concentrations were comparably enhanced. Positive correlations were found between DMSO and DMSP as well as DMSP and DMSO with chlorophyll a, which suggests a similar source for both compounds. Similar phytoplankton groups were identified as being important for the DMSO and DMSP pool, thus, the same algae taxa might produce both DMSP and DMSO. In contrast, phytoplankton seemed to play only a minor role for the DMS distribution in the western Pacific Ocean. The observed DMSPp : DMSOp ratios were very low and seem to be characteristic of oligotrophic tropical waters representing the extreme endpoint of the global DMSPp : DMSOp ratio vs. SST relationship. It is most likely that nutrient limitation and oxidative stress in the tropical West Pacific Ocean triggered enhanced DMSO production leading to an accumulation of DMSO in the sea surface. Positive correlations between DMSPd and CH4, as well as between DMSO (particulate and total) and CH4, were found along the transit. We conclude that both DMSP and DMSO serve as substrates for methanogenic bacteria in the western Pacific Ocean.

Description: Dynamical processes during the formation phase of the Arctic stratospheric vortex in autumn (from September to December) can introduce considerable interannual variability in the amount of ozone that is incorporated into the vortex. Chemistry in autumn tends to remove part of this variability because ozone relaxes towards equilibrium. As a quantitative measure of how important dynamical variability during vortex formation is for the winter ozone abundances above the Arctic we analyze which fraction of an ozone anomaly induced during vortex formation persists until early winter (3 January). The work is based on the Lagrangian Chemistry Transport Model ATLAS. In a case study, model runs for the winter 1999–2000 are used to assess the fate of an ozone anomaly artificially introduced during the vortex formation phase on 16 September. The runs provide information about the persistence of the induced ozone anomaly as a function of time, potential temperature and latitude. The induced ozone anomaly survives longer inside the polar vortex compared to outside the vortex. Half of the initial perturbation survives until 3 January at 540 K inside the polar vortex, with a rapid fall off towards higher levels, mainly due to NOx induced chemistry. Above 750 K the signal falls to values below 0.5%. Hence, dynamically induced ozone variability from the early vortex formation phase cannot significantly contribute to early winter variability above 750 K. At lower levels increasingly larger fractions of the initial perturbation survive, reaching 90% at 450 K. In this vertical range dynamical processes during the vortex formation phase are crucial for the ozone abundance in early winter.

Description: Intercomparison of two meteorological limited area models for quantitative precipitation forecast verification Natural Hazards and Earth System Science, 12, 591-606, 2012 Author(s): E. Oberto, M. Milelli, F. Pasi, and B. Gozzini The demand for verification of numerical models is still very high, especially for what concerns the operational Quantitative Precipitation Forecast (QPF) used, among others, for evaluating the issuing of warnings to the population. In this study, a comparative verification of the QPF, predicted by two operational Limited Area Models (LAMs) for the Italian territory is presented: COSMO-I7 (developed in the framework of the COSMO Consortium) and WRF-NMM (developed at NOAA-NCEP). The observational dataset is the precipitation recorded by the high-resolution non-GTS rain gauges network of the National Civil Protection Department (NCPD) over two years (2007–2008). Observed and forecasted precipitation have been treated as areal quantity (areal average of the values accumulated in 6 and 24 h periods) over the 102 "warning areas", defined by the NCPD both for administrative and hydrological purposes. Statistics are presented through a series of conventional indices (BIAS, POD and POFD) and, in addition, the Extreme Dependency Score (EDS) and the Base Rate (BS or 1-BS) have been used for keeping into account the vanishing of the indices as the events become rare. Results for long-period verification (the whole 2 yr) with increasing thresholds, seasonal trend (3 months period), diurnal error cycle and error maps, are presented. Results indicate that WRF has a general tendency of QPF overestimation for low thresholds and underestimation for higher ones, while COSMO-I7 tends to overestimate for all thresholds. Both models show a seasonal trend, with a bigger overestimation during summer and spring, while during autumn and winter the models tend to be more accurate.

Description: Pore formation during dehydration of a polycrystalline gypsum sample observed and quantified in a time-series synchrotron X-ray micro-tomography experiment Solid Earth, 3, 71-86, 2012 Author(s): F. Fusseis, C. Schrank, J. Liu, A. Karrech, S. Llana-Fúnez, X. Xiao, and K. Regenauer-Lieb We conducted an in-situ X-ray micro-computed tomography heating experiment at the Advanced Photon Source (USA) to dehydrate an unconfined 2.3 mm diameter cylinder of Volterra Gypsum. We used a purpose-built X-ray transparent furnace to heat the sample to 388 K for a total of 310 min to acquire a three-dimensional time-series tomography dataset comprising nine time steps. The voxel size of 2.2 μm 3 proved sufficient to pinpoint reaction initiation and the organization of drainage architecture in space and time. We observed that dehydration commences across a narrow front, which propagates from the margins to the centre of the sample in more than four hours. The advance of this front can be fitted with a square-root function, implying that the initiation of the reaction in the sample can be described as a diffusion process. Novel parallelized computer codes allow quantifying the geometry of the porosity and the drainage architecture from the very large tomographic datasets (2048 3 voxels) in unprecedented detail. We determined position, volume, shape and orientation of each resolvable pore and tracked these properties over the duration of the experiment. We found that the pore-size distribution follows a power law. Pores tend to be anisotropic but rarely crack-shaped and have a preferred orientation, likely controlled by a pre-existing fabric in the sample. With on-going dehydration, pores coalesce into a single interconnected pore cluster that is connected to the surface of the sample cylinder and provides an effective drainage pathway. Our observations can be summarized in a model in which gypsum is stabilized by thermal expansion stresses and locally increased pore fluid pressures until the dehydration front approaches to within about 100 μm. Then, the internal stresses are released and dehydration happens efficiently, resulting in new pore space. Pressure release, the production of pores and the advance of the front are coupled in a feedback loop.

Description: Coupling of climate models and ice sheet models by surface mass balance gradients: application to the Greenland Ice Sheet The Cryosphere, 6, 255-272, 2012 Author(s): M. M. Helsen, R. S. W. van de Wal, M. R. van den Broeke, W. J. van de Berg, and J. Oerlemans It is notoriously difficult to couple surface mass balance (SMB) results from climate models to the changing geometry of an ice sheet model. This problem is traditionally avoided by using only accumulation from a climate model, and parameterizing the meltwater run-off as a function of temperature, which is often related to surface elevation ( H s ). In this study, we propose a new strategy to calculate SMB, to allow a direct adjustment of SMB to a change in ice sheet topography and/or a change in climate forcing. This method is based on elevational gradients in the SMB field as computed by a regional climate model. Separate linear relations are derived for ablation and accumulation, using pairs of H s and SMB within a minimum search radius. The continuously adjusting SMB forcing is consistent with climate model forcing fields, also for initially non-glaciated areas in the peripheral areas of an ice sheet. When applied to an asynchronous coupled ice sheet – climate model setup, this method circumvents traditional temperature lapse rate assumptions. Here we apply it to the Greenland Ice Sheet (GrIS). Experiments using both steady-state forcing and glacial-interglacial forcing result in realistic ice sheet reconstructions.

Description: Estimating ice phenology on large northern lakes from AMSR-E: algorithm development and application to Great Bear Lake and Great Slave Lake, Canada The Cryosphere, 6, 235-254, 2012 Author(s): K.-K. Kang, C. R. Duguay, and S. E. L. Howell Time series of brightness temperatures ( T B ) from the Advanced Microwave Scanning Radiometer–Earth Observing System (AMSR-E) are examined to determine ice phenology variables on the two largest lakes of northern Canada: Great Bear Lake (GBL) and Great Slave Lake (GSL). T B measurements from the 18.7, 23.8, 36.5, and 89.0 GHz channels (H- and V- polarization) are compared to assess their potential for detecting freeze-onset/melt-onset and ice-on/ice-off dates on both lakes. The 18.7 GHz (H-pol) channel is found to be the most suitable for estimating these ice dates as well as the duration of the ice cover and ice-free seasons. A new algorithm is proposed using this channel and applied to map all ice phenology variables on GBL and GSL over seven ice seasons (2002–2009). Analysis of the spatio-temporal patterns of each variable at the pixel level reveals that: (1) both freeze-onset and ice-on dates occur on average about one week earlier on GBL than on GSL (Day of Year (DY) 318 and 333 for GBL; DY 328 and 343 for GSL); (2) the freeze-up process or freeze duration (freeze-onset to ice-on) takes a slightly longer amount of time on GBL than on GSL (about 1 week on average); (3) melt-onset and ice-off dates occur on average one week and approximately four weeks later, respectively, on GBL (DY 143 and 183 for GBL; DY 135 and 157 for GSL); (4) the break-up process or melt duration (melt-onset to ice-off) lasts on average about three weeks longer on GBL; and (5) ice cover duration estimated from each individual pixel is on average about three weeks longer on GBL compared to its more southern counterpart, GSL. A comparison of dates for several ice phenology variables derived from other satellite remote sensing products (e.g. NOAA Interactive Multisensor Snow and Ice Mapping System (IMS), QuikSCAT, and Canadian Ice Service Database) show that, despite its relatively coarse spatial resolution, AMSR-E 18.7 GHz provides a viable means for monitoring of ice phenology on large northern lakes.

Description: On the representation of immersion and condensation freezing in cloud models using different nucleation schemes Atmospheric Chemistry and Physics Discussions, 12, 7167-7209, 2012 Author(s): B. Ervens and G. Feingold Ice nucleation in clouds is often observed at temperatures 〉235 K, pointing to heterogeneous freezing as a predominant mechanism. Many models deterministically predict the number concentration of ice particles as a function of temperature and/or supersaturation. Laboratory experiments at constant temperature and/or supersaturation often report heterogeneous freezing as a stochastic, time-dependent process that follows classical nucleation theory which might appear to contradict singular freezing behavior. We explore the extent to which the choice of nucleation scheme (deterministic/stochastic, single/multiple contact angles θ) affects the prediction of the frozen ice nuclei (IN) fraction and cloud evolution. A box model with constant temperature and supersaturation is used to mimic published laboratory experiments of immersion freezing of kaolinite (~243 K), and the fitness of different nucleation schemes. Sensitivity studies show that agreement of all five schemes is restricted to the narrow parameter range (time, temperature, IN diameter) in the original laboratory studies. The schemes are implemented in an adiabatic parcel model that includes feedbacks of the formation and growth of drops and ice particles on supersaturation during the ascent of an air parcel. Model results show that feedbacks of droplets and ice on supersaturation limit ice nucleation events, often leading to smaller differences in number concentration of ice particles and ice water content (IWC) between stochastic and deterministic approaches than expected from the box model studies. However, the different parameterizations of θ distributions and time-dependencies are highly sensitive to IN size and can lead to great differences in predicted ice number concentrations and IWC between the different schemes. Finally, since the choice of nucleation scheme determines the temperature range over which nucleation occurs, at habit-prone temperatures (~253 K) different onset temperatures of freezing create variability in the initial inherent growth ratio of ice particles, which can lead to amplification or reduction in differences in predicted IWC.

Description: 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.

Description: A multi-model assessment of the efficacy of sea spray geoengineering Atmospheric Chemistry and Physics Discussions, 12, 7125-7166, 2012 Author(s): K. J. Pringle, K. S. Carslaw, T. Fan, G.W. Mann, A. Hill, P. Stier, K. Zhang, and H. Tost Artificially increasing the albedo of marine clouds by the mechanical emission of sea spray aerosol has been proposed as a geoengineering technique to slow the warming caused by anthropogenic greenhouse gases. A previous global model study found that only modest increases and sometimes even decreases in cloud drop number (CDN) concentrations would result from plausible emission scenarios. Here we extend that work to examine the conditions under which decreases in CDN can occur, and use three independent global models to quantify maximum achievable CDN changes. We find that decreases in CDN can occur when at least three of the following conditions are met: the injected particle number is 250–300 nm, the background aerosol loading is large (≥150 cm −3 ) and the in-cloud updraught velocity is low (

Description: Effects of seawater p CO 2 changes on the calcifying fluid of scleractinian corals Biogeosciences Discussions, 9, 2655-2689, 2012 Author(s): S. Hohn and A. Merico Rising atmospheric CO 2 concentrations due to anthropogenic emissions induce changes in the ocean carbonate chemistry and a drop in ocean pH. This acidification process is expected to harm calcifying organisms like coccolithophores, molluscs, echinoderms, and corals. A severe decline in coral abundance is, for example, expected by the end of this century with associated disastrous effects on reef ecosystems. Despite the growing importance of the topic, little progress has been made with respect to modelling the impact of acidification on coral calcification. Here we present a model for a coral polyp that simulates the carbonate system in four different compartments: the seawater, the polyp tissue, the coelenteron, and the calicoblastic layer. Precipitation of calcium carbonate takes place in the metabolically controlled calicoblastic layer beneath the polyp tissue. The model is adjusted to a state of activity as observed by direct microsensor measurements in the calcifying fluid. Simulated CO 2 perturbation experiments reveal decreasing calcification rates under elevated p CO 2 despite strong metabolic control of the calcifying fluid. Diffusion of CO 2 through the tissue into the calicoblastic layer increases with increasing seawater p CO 2 leading to decreased aragonite saturation in the calcifying fluid of the coral polyp. Our modelling study provides important insights into the complexity of the calcification process at the organism level and helps to quantify the effect of ocean acidification on corals.

Description: The role of the seagrass Posidonia oceanica in the cycling of trace elements Biogeosciences Discussions, 9, 2623-2653, 2012 Author(s): C. Sanz-Lázaro, P. Malea, E. T. Apostolaki, I. Kalantzi, A. Marín, and I. Karakassis The aim of this work was to study the role of the seagrass Posidonia oceanica on the cycling of a wide set of trace elements (Ag, As, Ba, Bi, Cd, Co, Cr, Cs, Cu, Fe, Ga, Li, Mn, Ni, Pb, Rb, Sr, Tl, V and Zn). We measured the concentration of these trace elements in the different compartments of P. oceanica (leaves, rhizomes, roots and epibiota) in a non-polluted seagrass meadow representative of the Mediterranean and calculated the annual budget from a mass balance. We provide novel data on accumulation dynamics of many trace elements in P. oceanica compartments and demonstrate that trace element accumulation patterns are mainly determined by plant compartment rather than by temporal variability. Epibiota was the compartment which showed the greatest concentrations for most trace elements. Thus, they constitute a key compartment when estimating trace element transfer to higher trophic levels by P. oceanica . For most trace elements, translocation seemed to be low and acropetal. Zn, Cd, Sr and Rb were the trace elements that showed the highest release rate through decomposition of plant detritus, while Cs, Tl and Bi the lowest. P. oceanica acts as a sink of potentially toxic trace elements (Ni, Cr, As and Ag), which can be sequestered, decreasing their bioavailability. P. oceanica may have a relevant role in the cycling of trace elements in the Mediterranean.

Description: 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.

Description: Fire history in western Patagonia from paired tree-ring fire-scar and charcoal records Climate of the Past, 8, 451-466, 2012 Author(s): A. Holz, S. Haberle, T. T. Veblen, R. De Pol-Holz, and J. Southon Fire history reconstructions are typically based on tree ages and tree-ring fire scars or on charcoal in sedimentary records from lakes or bogs, but rarely on both. In this study of fire history in western Patagonia (47–48° S) in southern South America (SSA) we compared three sedimentary charcoal records collected in bogs with tree-ring fire-scar data collected at 13 nearby sample sites. We examined the temporal and spatial correspondence between the two fire proxies and also compared them to published charcoal records from distant sites in SSA, and with published proxy reconstructions of regional climate variability and large-scale climate modes. Two of our three charcoal records record fire activity for the last 4 ka yr and one for the last 11 ka yr. For the last ca. 400 yr, charcoal accumulation peaks tend to coincide with high fire activity in the tree-ring fire scar records, but the charcoal records failed to detect some of the fire activity recorded by tree rings. Potentially, this discrepancy reflects low-severity fires that burn in herbaceous and other fine fuels without depositing charcoal in the sedimentary record. Periods of high fire activity tended to be synchronous across sample areas, across proxy types, and with proxy records of regional climatic variability as well as major climate drivers. Fire activity throughout the Holocene in western Patagonia has responded to regional climate variation affecting a broad region of southern South America that is teleconnected to both tropical- and high-latitude climate drivers-El Niño-Southern Oscillation and the Southern Annular Mode. An early Holocene peak in fire activity pre-dates any known human presence in our study area, and consequently implicates lightning as the ignition source. In contrast, the increased fire activity during the 20th century, which was concomitantly recorded by charcoal from all the sampled bogs and at all fire-scar sample sites, is attributed to human-set fires and is outside the range of variability characteristic of these ecosystems over many centuries and probably millennia.

Description: Exploring errors in paleoclimate proxy reconstructions using Monte Carlo simulations: paleotemperature from mollusk and coral geochemistry Climate of the Past, 8, 433-450, 2012 Author(s): M. Carré, J. P. Sachs, J. M. Wallace, and C. Favier Quantitative reconstructions of the past climate statistics from geochemical coral or mollusk records require quantified error bars in order to properly interpret the amplitude of the climate change and to perform meaningful comparisons with climate model outputs. We introduce here a more precise categorization of reconstruction errors, differentiating the error bar due to the proxy calibration uncertainty from the standard error due to sampling and variability in the proxy formation process. Then, we propose a numerical approach based on Monte Carlo simulations with surrogate proxy-derived climate records. These are produced by perturbing a known time series in a way that mimics the uncertainty sources in the proxy climate reconstruction. A freely available algorithm, MoCo, was designed to be parameterized by the user and to calculate realistic systematic and standard errors of the mean and the variance of the annual temperature, and of the mean and the variance of the temperature seasonality reconstructed from marine accretionary archive geochemistry. In this study, the algorithm is used for sensitivity experiments in a case study to characterize and quantitatively evaluate the sensitivity of systematic and standard errors to sampling size, stochastic uncertainty sources, archive-specific biological limitations, and climate non-stationarity. The results of the experiments yield an illustrative example of the range of variations of the standard error and the systematic error in the reconstruction of climate statistics in the Eastern Tropical Pacific. Thus, we show that the sample size and the climate variability are the main sources of the standard error. The experiments allowed the identification and estimation of systematic bias that would not otherwise be detected because of limited modern datasets. Our study demonstrates that numerical simulations based on Monte Carlo analyses are a simple and powerful approach to improve the understanding of the proxy records. We show that the standard error for the climate statistics linearly increases with the climate variability, which means that the accuracy of the error estimated by MoCo is limited by the climate non-stationarity.

Description: 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.

Description: 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.

Description: Towards a regional ocean forecasting system for the IBI (Iberia-Biscay-Ireland area): developments and improvements within the ECOOP project framework Ocean Science, 8, 143-159, 2012 Author(s): S. Cailleau, J. Chanut, J.-M. Lellouche, B. Levier, C. Maraldi, G. Reffray, and M. G. Sotillo The regional ocean operational system remains a key element in downscaling from large scale (global or basin scale) systems to coastal ones. It enables the transition between systems in which the resolution and the resolved physics are quite different. Indeed, coastal applications need a system to predict local high frequency events (inferior to the day) such as storm surges, while deep sea applications need a system to predict large scale lower frequency ocean features. In the framework of the ECOOP project, a regional system for the Iberia-Biscay-Ireland area has been upgraded from an existing V0 version to a V2. This paper focuses on the improvements from the V1 system, for which the physics are close to a large scale basin system, to the V2 for which the physics are more adapted to shelf and coastal issues. Strong developments such as higher regional physics resolution in the NEMO Ocean General Circulation Model for tides, non linear free surface and adapted vertical mixing schemes among others have been implemented in the V2 version. Thus, regional thermal fronts due to tidal mixing now appear in the latest version solution and are quite well positioned. Moreover, simulation of the stratification in shelf areas is also improved in the V2.

Description: Arctic sea ice variability and trends, 1979–2010 The Cryosphere Discussions, 6, 957-979, 2012 Author(s): D. J. Cavalieri and C. L. Parkinson Analyses of 32 yr (1979–2010) of Arctic sea ice extents and areas derived from satellite passive microwave radiometers are presented for the Northern Hemisphere as a whole and for nine Arctic regions. There is an overall negative yearly trend of −51.5 ± 4.1 × 10 3 km 2 yr −1 (−4.1 ± 0.3% decade −1 ) in sea ice extent for the hemisphere. The sea ice extent trends for the individual Arctic regions are all negative except for the Bering Sea: −3.9 ± 1.1 × 10 3 km 2 yr −1 (−8.7 ± 2.5% decade −1 ) for the Seas of Okhotsk and Japan, +0.3 ± 0.8 × 10 3 km 2 yr −1 (+1.2 ± 2.7% decade −1 ) for the Bering Sea, −4.4 ± 0.7 × 10 3 km 2 yr −1 (−5.1 ± 0.9% decade −1 ) for Hudson Bay, −7.6 ± 1.6 × 10 3 km 2 yr −1 (−8.5 ± 1.8% decade −1 ) for Baffin Bay/Labrador Sea, −0.5 ± 0.3 × 10 3 km 2 yr −1 (−5.9 ± 3.5% decade −1 ) for the Gulf of St. Lawrence, −6.5 ± 1.1 × 10 3 km 2 yr −1 (−8.6 ± 1.5% decade −1 ) for the Greenland Sea, −13.5 ± 2.3 × 10 3 km 2 yr −1 (−9.2 ± 1.6% decade −1 ) for the Kara and Barents Seas, −14.6 ± 2.3 × 10 3 km 2 yr −1 (−2.1 ± 0.3% decade −1 ) for the Arctic Ocean, and −0.9 ± 0.4 × 10 3 km 2 yr −1 (−1.3 ± 0.5% decade −1 ) for the Canadian Archipelago. Similarly, the yearly trends for sea ice areas are all negative except for the Bering Sea. On a seasonal basis for both sea ice extents and areas, the largest negative trend is observed for summer with the next largest negative trend being for autumn.

Description: On teaching styles of water educators and the impact of didactic training Hydrology and Earth System Sciences Discussions, 9, 2959-2986, 2012 Author(s): A. Pathirana, J. H. Koster, E. de Jong, and S. Uhlenbrook Solving today's complex hydrological problems requires originality, creative thinking and trans-disciplinary approaches. Hydrological education that was traditionally teacher centred, where the students look up to the teacher for expertise and information, should change to better prepare hydrologists to develop new knowledge and apply it in new contexts. An important first step towards this goal is to change the concept of education in the educators' minds. The results of an investigation to find out whether didactic training influences the beliefs of hydrology educators about their teaching styles is presented. Faculty of UNESCO-IHE has been offered a didactic certification program named University Teaching Qualification (UTQ). The hypothesis that UTQ training will significantly alter the teaching style of faculty at UNESCO-IHE from expert/formal authority traits towards facilitator/delegator traits was tested. A first survey was conducted among the entire teaching staff (total 101, response rate 58%). The results indicated that there are significantly higher traits of facilitator and delegator teaching styles among UTQ graduates compared to faculty who were not significantly trained in didactics. The second survey which was conducted among UTQ graduates (total 20, response rate 70%), enquiring after their teaching styles before and after UTQ, corroborated these findings.

Description: Characterization of deep aquifer dynamics using principal component analysis of sequential multilevel data Hydrology and Earth System Sciences, 16, 761-771, 2012 Author(s): D. Kurtzman, L. Netzer, N. Weisbrod, A. Nasser, E. R. Graber, and D. Ronen Two sequential multilevel profiles were obtained in an observation well opened to a 130-m thick, unconfined, contaminated aquifer in Tel Aviv, Israel. While the general profile characteristics of major ions, trace elements, and volatile organic compounds were maintained in the two sampling campaigns conducted 295 days apart, the vertical locations of high concentration gradients were shifted between the two profiles. Principal component analysis (PCA) of the chemical variables resulted in a first principal component which was responsible for ∼60% of the variability, and was highly correlated with depth. PCA revealed three distinct depth-dependent water bodies in both multilevel profiles, which were found to have shifted vertically between the sampling events. This shift cut across a clayey bed which separated the top and intermediate water bodies in the first profile, and was located entirely within the intermediate water body in the second profile. Continuous electrical conductivity monitoring in a packed-off section of the observation well revealed an event in which a distinct water body flowed through the monitored section ( v ∼ 150 m yr −1 ). It was concluded that the observed changes in the profiles result from dominantly lateral flow of water bodies in the aquifer rather than vertical flow. The significance of this study is twofold: (a) it demonstrates the utility of sequential multilevel observations from deep wells and the efficacy of PCA for evaluating the data; (b) the fact that distinct water bodies of 10 to 100 m vertical and horizontal dimensions flow under contaminated sites, which has implications for monitoring and remediation.

Description: Identifying the causes of differences in ozone production from the CB05 and CBMIV chemical mechanisms Geoscientific Model Development, 5, 257-268, 2012 Author(s): R. D. Saylor and A. F. Stein An investigation was conducted to identify the mechanistic differences between two versions of the carbon bond gas-phase chemical mechanism (CB05 and CBMIV) which consistently lead to larger ground-level ozone concentrations being produced in the CB05 version of the National Air Quality Forecasting Capability (NAQFC) modeling system even though the two parallel forecast systems utilize the same meteorology and base emissions and similar initial and boundary conditions. Box models of each of the mechanisms as they are implemented in the NAQFC were created and a set of 12 sensitivity simulations was designed. The sensitivity simulations independently probed the conceptual mechanistic differences between CB05 and CBMIV and were exercised over a 45-scenario simulation suite designed to emulate the wide range of chemical regimes encountered in a continental-scale atmospheric chemistry model. Results of the sensitivity simulations indicate that two sets of reactions that were included in the CB05 mechanism, but which were absent from the CBMIV mechanism, are the primary causes of the greater ozone production in the CB05 version of the NAQFC. One set of reactions recycles the higher organic peroxide species of CB05 (ROOH), resulting in additional photochemically reactive products that act to produce additional ozone in some chemical regimes. The other set of reactions recycles reactive nitrogen from less reactive forms back to NO 2 , increasing the effective NO x concentration of the system. In particular, the organic nitrate species (NTR), which was a terminal product for reactive nitrogen in the CBMIV mechanism, acts as a reservoir species in CB05 to redistribute NO x from major source areas to potentially NO x -sensitive areas where additional ozone may be produced in areas remote from direct NO x sources.

Description: The Nexus Land-Use model version 1.0, an approach articulating biophysical potentials and economic dynamics to model competition for land-use Geoscientific Model Development Discussions, 5, 571-638, 2012 Author(s): F. Souty, T. Brunelle, P. Dumas, B. Dorin, P. Ciais, R. Crassous, C. Müller, and A. Bondeau Interactions between food demand, biomass energy and forest preservation are driving both food prices and land-use changes, regionally and globally. This study presents a new model called Nexus Land-Use version 1.0 which describes these interactions through a generic representation of agricultural intensification mechanisms. The Nexus Land-Use model equations combine biophysics and economics into a single coherent framework to calculate crop yields, food prices, and resulting pasture and cropland areas within 12 regions inter-connected with each other by international trade. The representation of cropland and livestock production systems in each region relies on three components: (i) a biomass production function derived from the crop yield response function to inputs such as industrial fertilisers; (ii) a detailed representation of the livestock production system subdivided into an intensive and an extensive component, and (iii) a spatially explicit distribution of potential (maximal) crop yields prescribed from the Lund-Postdam-Jena global vegetation model for managed Land (LPJmL). The economic principles governing decisions about land-use and intensification are adapted from the Ricardian rent theory, assuming cost minimisation for farmers. The land-use modelling approach described in this paper entails several advantages. Firstly, it makes it possible to explore interactions among different types of biomass demand for food and animal feed, in a consistent approach, including indirect effects on land-use change resulting from international trade. Secondly, yield variations induced by the possible expansion of croplands on less suitable marginal lands are modelled by using regional land area distributions of potential yields, and a calculated boundary between intensive and extensive production. The model equations and parameter values are first described in details. Then, idealised scenarios exploring the impact of forest preservation policies or rising energy price on agricultural intensification are described, and their impacts on pasture and cropland areas are investigated.

Description: Editorial “Advances in Earth observation for water cycle science” Hydrology and Earth System Sciences, 16, 543-549, 2012 Author(s): D. Fernández-Prieto, P. van Oevelen, Z. Su, and W. Wagner

Description: Spiral structures and regularities in magnetic field variations and auroras History of Geo- and Space Sciences, 3, 1-31, 2012 Author(s): Y. I. Feldstein, L. I. Gromova, M. Förster, and A. E. Levitin The conception of spiral shaped precipitation regions, where solar corpuscles penetrate the upper atmosphere, was introduced into geophysics by C. Störmer and K. Birkeland at the beginning of the last century. Later, in the course of the XX-th century, spiral distributions were disclosed and studied in various geophysical phenomena. Most attention was devoted to spiral shapes in the analysis of regularities pertaining to the geomagnetic activity and auroras. We review the historical succession of perceptions about the number and positions of spiral shapes, that characterize the spatial-temporal distribution of magnetic disturbances. We describe the processes in the upper atmosphere, which are responsible for the appearance of spiral patterns. We considered the zones of maximal aurora frequency and of maximal particle precipitation intensity, as offered in the literature, in their connection with the spirals. We discuss the current system model, that is closely related to the spirals and that appears to be the source for geomagnetic field variations during magnetospheric substorms and storms. The currents in ionosphere and magnetosphere constitute together with field-aligned (along the geomagnetic field lines) currents (FACs) a common 3-D current system. At ionospheric heights, the westward and eastward electrojets represent characteristic elements of the current system. The westward electrojet covers the longitudinal range from the morning to the evening hours, while the eastward electrojet ranges from afternoon to near-midnight hours. The polar electrojet is positioned in the dayside sector at cusp latitudes. All these electrojets map along the magnetic field lines to certain plasma structures in the near-Earth space. The first spiral distribution of auroras was found based on observations in Antarctica for the nighttime-evening sector (N-spiral), and later in the nighttime-evening (N-spiral) and morning (M-spiral) sectors both in the Northern and Southern Hemispheres. The N- and M-spirals drawn in polar coordinates form an oval, along which one observes most often auroras in the zenith together with a westward electrojet. The nature of spiral distributions in geomagnetic field variations was unabmibuously interpreted after the discovery of the spiral's existence in the auroras had been established and this caused a change from the paradigm of the auroral zone to the paradigm of the auroral oval. Zenith forms of auroras are found within the boundaries of the auroral oval. The oval is therefore the region of most frequent precipitations of corpuscular fluxes with auroral energy, where anomalous geophysical phenomena occur most often and with maximum intensity. S. Chapman and L. Harang identified the existence of a discontinuity at auroral zone latitudes (Φ ∼ 67°) around midnight between the westward and eastward electrojets, that is now known as the Harang discontinuity. After the discovery of the auroral oval and the position of the westward electrojet along the oval, it turned out, that there is no discontinuity at a fixed latitude between the opposite electrojets, but rather a gap, the latitude of which varies smoothly between Φ ∼ 67° at midnight and Φ ∼ 73° at 20:00 MLT. In this respect the term ''Harang discontinuity'' represents no intrinsic phenomenon, because the westward electrojet does not experience any disruption in the midnight sector but continues without breaks from dawn to dusk hours.

Description: Observations of glyoxal and formaldehyde as metrics for the anthropogenic impact on rural photochemistry Atmospheric Chemistry and Physics Discussions, 12, 6049-6084, 2012 Author(s): J. P. DiGangi, S. B. Henry, A. Kammrath, E. S. Boyle, L. Kaser, R. Schnitzhofer, M. Graus, A. Turnipseed, J.-H. Park, R. J. Weber, R. S. Hornbrook, C. A. Cantrell, R. L. Maudlin III, S. Kim, Y. Nakashima, G. M. Wolfe, Y. Kajii, E. C. Apel, A. H. Goldstein, A. Guenther, T. Karl, A. Hansel, and F. N. Keutsch We present simultaneous fast, in-situ measurements of formaldehyde and glyoxal from two rural campaigns, BEARPEX 2009 and BEACHON-ROCS, both located in Pinus Ponderosa forests with emissions dominated by biogenic volatile organic compounds (VOCs). Despite considerable variability in the formaldehyde and glyoxal concentrations, the ratio of glyoxal to formaldehyde, R GF , displayed a very regular diurnal cycle over nearly 2 weeks of measurements. The only deviations in R GF were toward higher values and were the result of a biomass burning event during BEARPEX 2009 and very fresh anthropogenic influence during BEACHON-ROCS. Other rapid changes in glyoxal and formaldehyde concentrations have hardly any affect on R GF and could reflect transitions between low and high NO regimes. The trend of increased R GF from both anthropogenic reactive VOC mixtures and biomass burning compared to biogenic reactive VOC mixtures is robust due to the short timescales over which the observed changes in R GF occurred. Satellite retrievals, which suggest higher R GF for biogenic areas, are in contrast to our observed trends. It remains important to address this discrepancy, especially in view of the importance of satellite retrievals and in-situ measurements for model comparison. In addition, we propose that R GF , together with the absolute concentrations of glyoxal and formaldehyde, represents a useful metric for biogenic or anthropogenic reactive VOC mixtures. In particular, R GF yields information about not simply the VOCs in an airmass, but the VOC processing that directly couples ozone and secondary organic aerosol production.

Description: Characterization of aerosol and cloud water at a mountain site during WACS 2010: secondary organic aerosol formation through oxidative cloud processing Atmospheric Chemistry and Physics Discussions, 12, 6019-6047, 2012 Author(s): A. K. Y. Lee, K. L. Hayden, P. Herckes, W. R. Leaitch, J. Liggio, A. M. Macdonald, and J. P. D. Abbatt The water-soluble fractions of aerosol samples and cloud water collected during Whistler Aerosol and Cloud Study (WACS 2010) were analyzed using an Aerodyne aerosol mass spectrometer (AMS). This is the first study to report AMS organic spectra of re-aerosolized cloud water, and to make direct comparison between the AMS spectra of cloud water and aerosol samples collected at the same location. In general, the aerosol and cloud organic spectra were very similar, indicating that the cloud water organics likely originated from secondary organic aerosol (SOA) formed nearby. By using a photochemical reactor to oxidize both aerosol filter extracts and cloud water, we find evidence that fragmentation of aerosol water-soluble organics increases their volatility during oxidation. By contrast, enhancement of AMS-measurable organic mass by up to 30% was observed during aqueous-phase photochemical oxidation of cloud water organics. We propose that additional SOA material was produced by functionalizing dissolved organics via OH oxidation, where these dissolved organics are sufficiently volatile that they are not usually part of the aerosol. This work points out that water-soluble organic compounds of intermediate volatility (IVOC), such as cis -pinonic acid, produced via gas-phase oxidation of monoterpenes, can be important aqueous-phase SOA precursors in a biogenic-rich environment.

Description: 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.

Description: Evaluation of chemical transport model predictions of primary organic aerosol for air masses classified by particle-component-based factor analysis Atmospheric Chemistry and Physics Discussions, 12, 5939-6018, 2012 Author(s): C. A. Stroud, M. D. Moran, P. A. Makar, S. Gong, W. Gong, J. Zhang, J. G. Slowik, J. P. D. Abbatt, G. Lu, J. R. Brook, C. Mihele, Q. Li, D. Sills, K. B. Strawbridge, M. L. McGuire, and G. J. Evans Observations from the 2007 Border Air Quality and Meteorology Study (BAQS-Met 2007) in southern Ontario (ON), Canada, were used to evaluate Environment Canada's regional chemical transport model predictions of primary organic aerosol (POA). Environment Canada's operational numerical weather prediction model and the 2006 Canadian and 2005 US national emissions inventories were used as input to the chemical transport model (named AURAMS). Particle-component-based factor analysis was applied to aerosol mass spectrometer measurements made at one urban site (Windsor, ON) and two rural sites (Harrow and Bear Creek, ON) to derive hydrocarbon-like organic aerosol (HOA) factors. Co-located carbon monoxide (CO), PM 2.5 black carbon (BC), and PM 1 SO 4 measurements were also used for evaluation and interpretation, permitting a detailed diagnostic model evaluation. At the urban site, good agreement was observed for the comparison of daytime campaign PM 1 POA and HOA mean values: 1.1 μg m −3 vs. 1.2 μg m −3 , respectively. However, a POA overprediction was evident on calm nights due to an overly-stable model surface layer. Biases in model POA predictions trended from positive to negative with increasing HOA values. This trend has several possible explanations, including (1) underweighting of urban locations in particulate matter (PM) spatial surrogate fields, (2) overly-coarse model grid spacing for resolving urban-scale sources, and (3) lack of a model particle POA evaporation process during dilution of vehicular POA tail-pipe emissions to urban scales. Furthermore, a trend in POA bias was observed at the urban site as a function of the BC/HOA ratio, suggesting a possible association of POA underprediction for diesel combustion sources. For several time periods, POA overprediction was also observed for sulphate-rich plumes, suggesting that our model POA fractions for the PM 2.5 chemical speciation profiles may be too high for these point sources. At the rural Harrow site, significant underpredictions in PM 1 POA concentration were found compared to observed HOA concentration and were associated, based on back-trajectory analysis, with (1) transport from the Detroit/Windsor urban complex, (2) longer-range transport from the US Midwest, and (3) biomass burning. Daytime CO concentrations were significantly overpredicted at Windsor but were unbiased at Harrow. Collectively, these biases provide support for a hypothesis that combines a current underweighting of PM spatial surrogate fields for urban locations with insufficient model vertical mixing for sources close to the urban measurement sites. The magnitude of the area POA emissions sources in the US and Canadian inventories (e.g., food cooking, road and soil dust, waste disposal burning) suggests that more effort should be placed at reducing uncertainties in these sectors, especially spatial and temporal surrogates.

Description: Direct observations of diel biological CO 2 fixation in the oceans Biogeosciences Discussions, 9, 2153-2168, 2012 Author(s): H. Thomas, S. E. Craig, B. J. W. Greenan, W. Burt, G. J. Herndl, S. Higginson, L. Salt, E. H. Shadwick, and J. Urrego-Blanco Much of the variability in the surface ocean's carbon cycle can be attributed to the availability of sunlight, through processes such as heat fluxes and photosynthesis, which regulate over a wide range of time scales. The critical processes occurring on timescales of a day or less, however, have undergone few investigations, and most of these have been limited to a time span of several days to months, or exceptionally, for longer periods. Optical methods have helped to infer short-term biological variability, however corresponding investigations of the oceanic CO 2 system are lacking. We employ high-frequency CO 2 and optical observations covering the full seasonal cycle on the Scotian Shelf, Northwestern Atlantic Ocean, in order to unravel diel periodicity of the surface ocean carbon cycle and its effects on annual budgets. Significant diel periodicity occurs only if the water column is sufficiently stable as observed during seasonal warming. During that time biological CO 2 drawdown, or net community production (NCP), is delayed for several hours relative to the onset of photosynthetically available radiation (PAR), due to diel cycles in chlorophyll- a concentration and to grazing, both of which, we suggest, inhibit NCP in the early morning hours. In summer, NCP decreases by more than 90 %, coinciding with the seasonal minimum of the mixed layer depth and resulting in the disappearance of the diel CO 2 periodicity in the surface waters.

Description: Solar wind and geomagnetism: toward a standard classification of geomagnetic activity from 1868 to 2009 Annales Geophysicae, 30, 421-426, 2012 Author(s): J. L. Zerbo, C. Amory Mazaudier, F. Ouattara, and J. D. Richardson We examined solar activity with a large series of geomagnetic data from 1868 to 2009. We have revisited the geomagnetic activity classification scheme of Legrand and Simon (1989) and improve their scheme by lowering the minimum Aa index value for shock and recurrent activity from 40 to 20 nT. This improved scheme allows us to clearly classify about 80% of the geomagnetic activity in this time period instead of only 60% for the previous Legrand and Simon classification.

Description: A statistical study of the performance of the Hakamada-Akasofu-Fry version 2 numerical model in predicting solar shock arrival times at Earth during different phases of solar cycle 23 Annales Geophysicae, 30, 405-419, 2012 Author(s): S. M. P. McKenna-Lawlor, C. D. Fry, M. Dryer, D. Heynderickx, K. Kecskemety, K. Kudela, and J. Balaz The performance of the Hakamada Akasofu-Fry, version 2 (HAFv.2) numerical model, which provides predictions of solar shock arrival times at Earth, was subjected to a statistical study to investigate those solar/interplanetary circumstances under which the model performed well/poorly during key phases (rise/maximum/decay) of solar cycle 23. In addition to analyzing elements of the overall data set (584 selected events) associated with particular cycle phases, subsets were formed such that those events making up a particular sub-set showed common characteristics. The statistical significance of the results obtained using the various sets/subsets was generally very low and these results were not significant as compared with the hit by chance rate (50%). This implies a low level of confidence in the predictions of the model with no compelling result encouraging its use. However, the data suggested that the success rates of HAFv.2 were higher when the background solar wind speed at the time of shock initiation was relatively fast. Thus, in scenarios where the background solar wind speed is elevated and the calculated success rate significantly exceeds the rate by chance, the forecasts could provide potential value to the customer. With the composite statistics available for solar cycle 23, the calculated success rate at high solar wind speed, although clearly above 50%, was indicative rather than conclusive. The RMS error estimated for shock arrival times for every cycle phase and for the composite sample was in each case significantly better than would be expected for a random data set. Also, the parameter "Probability of Detection, yes" (PODy) which presents the Proportion of Yes observations that were correctly forecast (i.e. the ratio between the shocks correctly predicted and all the shocks observed), yielded values for the rise/maximum/decay phases of the cycle and using the composite sample of 0.85, 0.64, 0.79 and 0.77, respectively. The statistical results obtained through detailed analysis of the available data provided insights into how changing circumstances on the Sun and in interplanetary space can affect the performance of the model. Since shock arrival predictions are widely utilized in making commercially significant decisions re. protecting space assets, the present detailed archival studies can be useful in future operational decision making during solar cycle 24. It would be of added value in this context to use Briggs-Rupert methodology to estimate the cost to an operator of acting on an incorrect forecast.

Description: Extension of an assessment model of ship traffic exhaust emissions for particulate matter and carbon monoxide Atmospheric Chemistry and Physics, 12, 2641-2659, 2012 Author(s): J.-P. Jalkanen, L. Johansson, J. Kukkonen, A. Brink, J. Kalli, and T. Stipa A method is presented for the evaluation of the exhaust emissions of marine traffic, based on the messages provided by the Automatic Identification System (AIS), which enable the positioning of ship emissions with a high spatial resolution (typically a few tens of metres). The model also takes into account the detailed technical data of each individual vessel. The previously developed model was applicable for evaluating the emissions of NO x , SO x and CO 2 . This paper addresses a substantial extension of the modelling system, to allow also for the mass-based emissions of particulate matter (PM) and carbon monoxide (CO). The presented Ship Traffic Emissions Assessment Model (STEAM2) allows for the influences of accurate travel routes and ship speed, engine load, fuel sulphur content, multiengine setups, abatement methods and waves. We address in particular the modeling of the influence on the emissions of both engine load and the sulphur content of the fuel. The presented methodology can be used to evaluate the total PM emissions, and those of organic carbon, elemental carbon, ash and hydrated sulphate. We have evaluated the performance of the extended model against available experimental data on engine power, fuel consumption and the composition-resolved emissions of PM. We have also compared the annually averaged emission values with those of the corresponding EMEP inventory, As example results, the geographical distributions of the emissions of PM and CO are presented for the marine regions of the Baltic Sea surrounding the Danish Straits.

Description: The sudden stratospheric warming of the Arctic winter 2009/2010: comparison to other recent warm winters Atmospheric Chemistry and Physics Discussions, 12, 7243-7271, 2012 Author(s): J. Kuttippurath and G. Nikulin The Arctic winter 2009/10 was moderately cold in December. A minor warming occurred around mid-December due to a wave 2 amplification split the lower stratospheric vortex into two lobes. The vortices merged again and formed a relatively large vortex in a few days. The temperatures began to rise by mid-January and triggered a major sudden stratospheric warming (SSW) by the reversal of westerlies in late (24–26) January, driven by a planetary wave 1 with a peak amplitude of about 100 m 2 s −2 at 60° N/10 hPa. The momentum flux associated with this warming showed the largest value in the recent winters, about 450 m 2 s −2 at 60° N/10 hPa. The associated vortex split confined to altitudes below 10 hPa and hence, the major warming (MW) was a vortex displacement event. Large amounts of Eliassen-Palm (EP) and wave 2 EP fluxes (3.9 ×10 5 kg s −2 ) are found shortly before the MW event at 100 hPa over 45–75° N, suggesting a tropospheric preconditioning of the MW event. We observe an increase in SSWs in the Arctic in recent years, as there were 6 MWs in 6 out of the 7 winters of 2003/04–2009/10, which confirms the conclusions of previous studies on the SSWs in winters prior to 2003/04. Each MW event was unique as far as its evolution and related polar processes were concerned. As compared to the MWs in the recent Arctic winters, the strongest MW was observed in 2008/09 and was initiated by a wave 2 event. A detailed diagnosis of ozone loss during the past fifteen years shows that the loss is inversely proportional to the intensity and timing of SSWs in each winter, where early MWs lead to minimal loss. The ozone loss shows a good correlation with the zonal mean amplitude of zonal winds in January over 60–90° N, suggesting a proxy for MWs in the Arctic winters.

Description: Observing the continental-scale carbon balance: assessment of sampling complementarity and redundancy in a terrestrial assimilation system by means of quantitative network design Atmospheric Chemistry and Physics Discussions, 12, 7211-7242, 2012 Author(s): T. Kaminski, P. J. Rayner, M. Voßbeck, M. Scholze, and E. Koffi This paper investigates the relationship between the heterogeneity of the terrestrial carbon cycle and the optimal design of observing networks to constrain it. We combine the methods of quantitative network design and carbon-cycle data assimilation to a hierarchy of increasingly heterogeneous descriptions of the European terrestrial biosphere as indicated by increasing diversity of plant functional types. We employ three types of observations, flask measurements of CO 2 concentrations, continuous measurements of CO 2 and pointwise measurements of CO 2 flux. We show that flux measurements are extremely efficient for relatively homogeneous situations but not robust against increasing or unknown complexity. Here a hybrid approach is necessary and we recommend its use in the development of integrated carbon observing systems.

Description: 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.

Description: 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.

Description: 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.

Description: The regulation of the air: a hypothesis Solid Earth, 3, 87-96, 2012 Author(s): E. G. Nisbet, C. M. R. Fowler, and R. E. R. Nisbet We propose the hypothesis that natural selection, acting on the specificity or preference for CO 2 over O 2 of the enzyme rubisco (ribulose-1,5-bisphosphate carboxylase/oxygenase), has controlled the CO 2 :O 2 ratio of the atmosphere since the evolution of photosynthesis and has also sustained the Earth's greenhouse-set surface temperature. Rubisco works in partnership with the nitrogen-fixing enzyme nitrogenase to control atmospheric pressure. Together, these two enzymes control global surface temperature and indirectly the pH and oxygenation of the ocean. Thus, the co-evolution of these two enzymes may have produced clement conditions on the Earth's surface, allowing life to be sustained.

Description: Modelling sub-grid wetland in the ORCHIDEE global land surface model: evaluation against river discharges and remotely sensed data Geoscientific Model Development Discussions, 5, 683-735, 2012 Author(s): B. Ringeval, B. Decharme, S. L. Piao, P. Ciais, F. Papa, N. de Noblet-Ducoudré, C. Prigent, P. Friedlingstein, I. Gouttevin, C. Koven, and A. Ducharne The quality of the global hydrological simulations performed by Land Surface Models (LSMs) strongly depends on processes that occur at unresolved spatial scales. Approaches such as TOPMODEL have been developed, which allow soil moisture redistribution within each grid-cell, based upon sub-grid scale topography. Moreover, the coupling between TOPMODEL and a LSM appears as a potential way to simulate wetland extent dynamic and its sensitivity to climate, a recently identified research problem for biogeochemical modelling, including methane emissions. Global evaluation of the coupling between TOPMODEL and an LSM is difficult, and prior attempts have been indirect, based on the evaluation of the simulated river flow. This study presents a new way to evaluate this coupling, within the ORCHIDEE LSM, using remote sensing data of inundated areas. Because of differences in nature between the satellite derived information – inundation extent – and the variable diagnosed by TOPMODEL/ORCHIDEE – area at maximum soil water content –, the evaluation focuses on the spatial distribution of these two quantities as well as on their temporal variation. Despite some difficulties in exactly matching observed localized inundated events, we obtain a rather good agreement in the distribution of these two quantities at a global scale. Floodplains are not accounted for in the model, and this is a major limitation. The difficulty of reproducing the year-to-year variability of the observed inundated area (for instance, the decreasing trend by the end of 90s) is also underlined. Classical indirect evaluation based on comparison between simulated and observed riverflow is also performed and underlines difficulties to simulate riverflow after coupling with TOPMODEL. The relationship between inundation and river flow at the basin scale in the model is analyzed, using both methods (evaluation against remote sensing data and riverflow). Finally, we discuss the potential of the TOPMODEL/LSM coupling to simulate wetland areas. A major limitation of the coupling for this purpose is linked to its ability to simulate a global wetland coverage consistent with the commonly used datasets. However, it seems to be a good opportunity to account for the wetland areas sensitivity to the climate and thus to simulate its temporal variability.

Description: River monitoring from satellite radar altimetry in the Zambezi River Basin Hydrology and Earth System Sciences Discussions, 9, 3203-3235, 2012 Author(s): C. I. Michailovsky, S. McEnnis, P. A. M. Berry, R. Smith, and P. Bauer-Gottwein Satellite radar altimetry can be used to monitor surface water levels from space. While current and past altimetry missions were designed to study oceans, retracking the waveforms returned over land allows data to be retrieved for smaller water bodies or narrow rivers. In this study, retracked Envisat altimetry data was extracted over the Zambezi River Basin using a detailed river mask based on Landsat imagery. This allowed for stage measurements to be obtained for rivers down to 80 m wide with an RMSE relative to in situ levels of 0.32 to 0.72 m at different locations. The altimetric levels were then converted to discharge using three different methods adapted to different data-availability scenarios: first with an in situ rating curve available, secondly with one simultaneous field measurement of cross-section and discharge, and finally with only historical discharge data available. For the two locations at which all three methods could be applied the accuracies of the different methods were found to be comparable, with RMSE values ranging from 5.5 to 7.4 % terms of high flow estimation relative to in situ gauge measurements. The precision obtained with the different methods was analyzed by running Monte Carlo simulations and also showed comparable values for the three approaches with standard deviations found between 8.2 and 25.8 % of the high flow estimates.

Description: Water management simulation games and the construction of knowledge Hydrology and Earth System Sciences Discussions, 9, 3063-3085, 2012 Author(s): M. Rusca, J. Heun, and K. Schwartz In recent years simulations have become an important part of teaching activities. The reasons behind the popularity of simulation games are twofold. On the one hand, emerging theories on how people learn have called for an experienced-based learning approach. On the other hand, the demand for water management professionals has changed. Three important developments are having considerable consequences for water management programmes, which educate and train these professionals. These developments are the increasing emphasis on integration in water management, the characteristics and speed of reforms in the public sector and the shifting state-society relations in many countries. In response to these developments, demand from the labour market is oriented toward water professionals who need to have both a specialist in-depth knowledge in their own field, as well as the ability to understand and interact with other disciplines and interests. In this context, skills in negotiating, consensus building and working in teams are considered essential for all professionals. In this paper we argue that simulation games have an important role to play in (actively) educating students and training the new generation of water professionals to respond to the above-mentioned challenges. At the same time, simulations are not a panacea for learners and teachers. Challenges of using simulations games include the demands it places on the teacher. Setting up the simulation game, facilitating the delivery and ensuring that learning objectives are achieved requires considerable knowledge and experience as well as considerable time-inputs of the teacher. Moreover, simulation games usually incorporate a case-based learning model, which may neglect or underemphasize theories and conceptualization. For simulations to be effective they have to be embedded in this larger theoretical and conceptual framework. Simulations, therefore, complement rather than substitute traditional teaching methods.

Description: Evaluation of a complementary based model for mapping land surface evapotranspiration Hydrology and Earth System Sciences Discussions, 9, 3029-3062, 2012 Author(s): Z. Sun, Q. Wang, Z. Ouyang, and Y. Yang A modified Priestley-Taylor (P-T) equation was proposed by Venturini et al. (2008) to map actual evapotranspiration (ET) based solely on satellite remote sensing data, involving a parameter based on a scaled temperature between dew point temperature and surface temperature. In this study, however, theoretical analyses and field experimental evidence show that it is hard to obtain this scaled temperature using dew point temperature and surface temperature. This study also presents a new parameterization method using air temperature, surface temperature, and surface temperature of a reference dry surface. The actual ET estimates obtained by means of our proposed parameterization method are validated at a site scale, and a case study is conducted to map actual ET from Advanced Spaceborne Thermal Emission and Reflection radiometer (ASTER) images using our proposed method. Results of ground-based validation and a case study of mapping ET using ASTER images indicate that the improvement on the modified P-T equation proposed by Venturini et al. (2008) can contribute to generating reliable actual ET.

Description: Prioritization of water management under climate change and urbanization using multi-criteria decision making methods Hydrology and Earth System Sciences, 16, 801-814, 2012 Author(s): J.-S. Yang, E.-S. Chung, S.-U. Kim, and T.-W. Kim This paper quantifies the transformed effectiveness of alternatives for watershed management caused by climate change and urbanization and prioritizes five options using multi-criteria decision making techniques. The climate change scenarios (A1B and A2) were obtained by using a statistical downscaling model (SDSM), and the urbanization scenario by surveying the existing urban planning. The flow and biochemical oxygen demand (BOD) concentration duration curves were derived, and the numbers of days required to satisfy the environmental flow requirement and the target BOD concentration were counted using the Hydrological Simulation Program-Fortran (HSPF) model. In addition, five feasible alternatives were prioritized by using multi-criteria decision making techniques, based on the driving force-pressure-state-impact-response (DPSIR) framework and cost component. Finally, a sensitivity analysis approach for MCDM methods was conducted to reduce the uncertainty of weights. The result indicates that the most sensitive decision criterion is cost, followed by criteria response, driving force, impact, state and pressure in that order. As it is certain that the importance of cost component is over 0.127, construction of a small wastewater treatment plant will be the most preferred alternative in this application.

Description: Influence of parallel computational uncertainty on simulations of the Coupled General Climate Model Geoscientific Model Development, 5, 313-319, 2012 Author(s): Z. Song, F. Qiao, X. Lei, and C. Wang This paper investigates the impact of the parallel computational uncertainty due to the round-off error on climate simulations using the Community Climate System Model Version 3 (CCSM3). A series of sensitivity experiments have been conducted and the analyses are focused on the Global and Nino3.4 average sea surface temperatures (SST). For the monthly time series, it is shown that the amplitude of the deviation induced by the parallel computational uncertainty is the same order as that of the climate system change. However, the ensemble mean method can reduce the influence and the ensemble member number of 15 is enough to ignore the uncertainty. For climatology, the influence can be ignored when the climatological mean is calculated by using more than 30-yr simulations. It is also found that the parallel computational uncertainty has no distinguishable effect on power spectrum analysis of climate variability such as ENSO. Finally, it is suggested that the influence of the parallel computational uncertainty on Coupled General Climate Models (CGCMs) can be a quality standard or a metric for developing CGCMs.

Description: Precipitation fields interpolated from gauge stations versus a merged radar-gauge precipitation product: influence on modelled soil moisture at local scale and at SMOS scale Hydrology and Earth System Sciences Discussions, 9, 3385-3413, 2012 Author(s): J. T. dall'Amico, W. Mauser, F. Schlenz, and H. Bach For the validation of coarse resolution soil moisture products from missions such as the Soil Moisture and Ocean Salinity (SMOS) mission, hydrological modelling of soil moisture is an important tool. The spatial distribution of precipitation is among the most crucial input data for such models. Thus, reliable time series of precipitation fields are required, but these often need to be interpolated from data delivered by scarcely distributed gauge station networks. In this study, a commercial precipitation product derived by Meteomedia AG from merging radar and gauge data is introduced as a novel means of adding the promising area-distributed information given by a radar network to the more accurate, but point-like measurements from a gauge station network. This precipitation product is first validated against an independent gauge station network. Further, the novel precipitation product is assimilated into the hydrological land surface model PROMET for the Upper Danube Catchment in southern Germany, one of the major SMOS calibration and validation sites in Europe. The modelled soil moisture fields are compared to those obtained when the operational interpolation from gauge station data is used to force the model. The results suggest that the assimilation of the novel precipitation product can lead to deviations of modelled soil moisture in the order of 0.15 m 3 m −3 on small spatial (∼1 km 2 ) and short temporal resolutions (∼1 day). As expected, after spatial aggregation to the coarser grid on which SMOS data are delivered (~195 km 2 ), these differences are reduced to the order of 0.04 m 3 m −3 , which is the accuracy benchmark for SMOS. The results of both model runs are compared to brightness temperatures measured by the airborne L-band radiometer EMIRAD during the SMOS Validation Campaign 2010. Both comparisons yield equally good correlations, confirming the model's ability to realistically model soil moisture fields in the test site. The fact that the two model runs perform similarly in the comparison is likely associated with the lack of substantial rain events before the days on which EMIRAD was flown.

Description: An integrated uncertainty and ensemble-based data assimilation approach for improved operational streamflow predictions Hydrology and Earth System Sciences, 16, 815-831, 2012 Author(s): M. He, T. S. Hogue, S. A. Margulis, and K. J. Franz The current study proposes an integrated uncertainty and ensemble-based data assimilation framework (ICEA) and evaluates its viability in providing operational streamflow predictions via assimilating snow water equivalent (SWE) data. This step-wise framework applies a parameter uncertainty analysis algorithm (ISURF) to identify the uncertainty structure of sensitive model parameters, which is subsequently formulated into an Ensemble Kalman Filter (EnKF) to generate updated snow states for streamflow prediction. The framework is coupled to the US National Weather Service (NWS) snow and rainfall-runoff models. Its applicability is demonstrated for an operational basin of a western River Forecast Center (RFC) of the NWS. Performance of the framework is evaluated against existing operational baseline (RFC predictions), the stand-alone ISURF and the stand-alone EnKF. Results indicate that the ensemble-mean prediction of ICEA considerably outperforms predictions from the other three scenarios investigated, particularly in the context of predicting high flows (top 5th percentile). The ICEA streamflow ensemble predictions capture the variability of the observed streamflow well, however the ensemble is not wide enough to consistently contain the range of streamflow observations in the study basin. Our findings indicate that the ICEA has the potential to supplement the current operational (deterministic) forecasting method in terms of providing improved single-valued (e.g., ensemble mean) streamflow predictions as well as meaningful ensemble predictions.

Description: Advancing data assimilation in operational hydrologic forecasting: progresses, challenges, and emerging opportunities Hydrology and Earth System Sciences Discussions, 9, 3415-3472, 2012 Author(s): Y. Liu, A. H. Weerts, M. Clark, H.-J. Hendricks Franssen, S. Kumar, H. Moradkhani, D.-J. Seo, D. Schwanenberg, P. Smith, A. I. J. M. van Dijk, N. van Velzen, M. He, H. Lee, S. J. Noh, O. Rakovec, and P. Restrepo Data assimilation (DA) holds considerable potential for improving hydrologic predictions as demonstrated in numerous research studies. However, advances in hydrologic DA research have not been adequately or timely implemented into operational forecast systems to improve the skill of forecasts to better inform real-world decision making. This is due in part to a lack of mechanisms to properly quantify the uncertainty in observations and forecast models in real-time forecasting situations and to conduct the merging of data and models in a way that is adequately efficient and transparent to operational forecasters. The need for effective DA of useful hydrologic data into the forecast process has become increasingly recognized in recent years. This motivated a hydrologic DA workshop in Delft, The Netherlands in November 2010, which focused on advancing DA in operational hydrologic forecasting and water resources management. As an outcome of the workshop, this paper reviews, in relevant detail, the current status of DA applications in both hydrologic research and operational practices, and discusses the existing or potential hurdles and challenges in transitioning hydrologic DA research into cost-effective operational forecasting tools, as well as the potential pathways and newly emerging opportunities for overcoming these challenges. Several related aspects are discussed, including (1) theoretical or mathematical considerations in DA algorithms, (2) the estimation of different types of uncertainty, (3) new observations and their objective use in hydrologic DA, (4) the use of DA for real-time control of water resources systems, and (5) the development of community-based, generic DA tools for hydrologic applications. It is recommended that cost-effective transition of hydrologic DA from research to operations should be helped by developing community-based, generic modelling and DA tools or frameworks, and through fostering collaborative efforts among hydrologic modellers, DA developers, and operational forecasters.

Description: Impact of climate change on sediment yield in the Mekong River Basin: a case study of the Nam Ou Basin, Lao PDR Hydrology and Earth System Sciences Discussions, 9, 3339-3384, 2012 Author(s): B. Shrestha, M. S. Babel, S. Maskey, A. van Griensven, S. Uhlenbrook, A. Green, and I. Akkharath This paper evaluates the impact of climate change on sediment yield in the Nam Ou Basin located in Northern Laos. The Soil and Water Assessment Tool (SWAT) is used to assess future changes in sediment flux attributable to climate change. Future precipitation and temperature series are constructed through a delta change approach. As per the results, in general, temperature as well as precipitation show increasing trends in both scenarios, A2 and B2. However, monthly precipitation shows both increasing and decreasing trends. The simulation results exhibit that the wet and dry seasonal and annual stream discharges are likely to increase (by up to 15, 17 and 14% under scenario A2; and 11, 5 and 10% under scenario B2 respectively) in the future, which will lead to increased wet and dry seasonal and annual sediment yields (by up to 39, 28 and 36% under scenario A2; and 23, 12 and 22% under scenario B2 respectively). A higher discharge and more sediment flux are expected during the wet seasons, although the changes, percentage-wise, are observed to be higher during the dry months. In conclusion, the sediment yield from the Nam Ou Basin is likely to increase with climate change, which strongly suggests the need for basin-wide sediment management strategies in order to reduce the negative impact of this change.

Description: Assessment of a physical-biogeochemical coupled model system for operational service in the Baltic Sea Ocean Science Discussions, 9, 835-876, 2012 Author(s): Z. Wan, J. She, M. Maar, L. Jonasson, and J. Baasch-Larsen Thanks to the abundant observation data, we are able to deploy the traditional point-to-point comparison and statistical measures in combination with a comprehensive model validation scheme to assess the skills of the biogeochemical model ERGOM in providing an operational service for the Baltic Sea. The model assessment concludes that the operational products can resolve the main observed seasonal features for phytoplankton biomass, dissolved inorganic nitrogen, dissolved inorganic phosphorus and dissolved oxygen in euphotic layers, as well as their vertical profiles. This assessment reflects that the model errors of the operational system at the current stage are mainly caused by insufficient light penetration, excessive organic particle export downward, insufficient regional adaptation and some of improper initialization. This study highlights the importance of applying multiple schemes in order to assess model skills rigidly and identify main causes for major model errors.

Description: Numerical tools to estimate the flux of a gas across the air-water interface and assess the heterogeny of its forcing functions Ocean Science Discussions, 9, 909-975, 2012 Author(s): V. M. N. de C. da S. Vieira A numerical tool was developed for the estimation of gas fluxes across the air water interface. The primary objective is to use it to estimate CO 2 fluxes. Nevertheless application to other gases is easily accomplished by changing the values of the parameters related to the physical properties of the gases. A user friendly software was developed allowing to build upon a standard kernel a custom made gas flux model with the preferred parametrizations. These include single or double layer models; several numerical schemes for the effects of wind in the air-side and water-side transfer velocities; the effect of turbulence from current drag with the bottom; and the effects on solubility of water temperature, salinity, air temperature and pressure. It was also developed an analysis which decomposes the difference between the fluxes in a reference situation and in alternative situations into its several forcing functions. This analysis relies on the Taylor expansion of the gas flux model, requiring the numerical estimation of partial derivatives by a multivariate version of the collocation polynomial. Both the flux model and the difference decomposition analysis were tested with data taken from surveys done in the lagoonary system of Ria Formosa, south Portugal, in which the CO 2 fluxes were estimated using the IRGA and floating chamber method whereas the CO 2 concentrations were estimated using the IRGA and degasification chamber. Observations and estimations show a remarkable fit.

Description: Precipitation as the main driver of Neoglacial fluctuations of Gualas glacier, Northern Patagonian Icefield Climate of the Past, 8, 519-534, 2012 Author(s): S. Bertrand, K. A. Hughen, F. Lamy, J.-B. W. Stuut, F. Torrejón, and C. B. Lange Glaciers are frequently used as indicators of climate change. However, the link between past glacier fluctuations and climate variability is still highly debated. Here, we investigate the mid- to late-Holocene fluctuations of Gualas Glacier, one of the northernmost outlet glaciers of the Northern Patagonian Icefield, using a multi-proxy sedimentological and geochemical analysis of a 15 m long fjord sediment core from Golfo Elefantes, Chile, and historical documents from early Spanish explorers. Our results show that the core can be sub-divided into three main lithological units that were deposited under very different hydrodynamic conditions. Between 5400 and 4180 cal yr BP and after 750 cal yr BP, sedimentation in Golfo Elefantes was characterized by the rapid deposition of fine silt, most likely transported by fluvio-glacial processes. By contrast, the sediment deposited between 4130 and 850 cal yr BP is composed of poorly sorted sand that is free of shells. This interval is particularly marked by high magnetic susceptibility values and Zr concentrations, and likely reflects a major advance of Gualas glacier towards Golfo Elefantes during the Neoglaciation. Several thin silt layers observed in the upper part of the core are interpreted as secondary fluctuations of Gualas glacier during the Little Ice Age, in agreement with historical and dendrochronological data. Our interpretation of the Golfo Elefantes glaciomarine sediment record in terms of fluctuations of Gualas glacier is in excellent agreement with the glacier chronology proposed for the Southern Patagonian Icefield, which is based on terrestrial (moraine) deposits. By comparing our results with independent proxy records of precipitation and sea surface temperature, we suggest that the fluctuations of Gualas glacier during the last 5400 yr were mainly driven by changes in precipitation in the North Patagonian Andes.

Description: A critical humidity threshold for monsoon transitions Climate of the Past, 8, 535-544, 2012 Author(s): J. Schewe, A. Levermann, and H. Cheng Monsoon systems around the world are governed by the so-called moisture-advection feedback. Here we show that, in a minimal conceptual model, this feedback implies a critical threshold with respect to the atmospheric specific humidity q o over the ocean adjacent to the monsoon region. If q o falls short of this critical value q o c , monsoon rainfall over land cannot be sustained. Such a case could occur if evaporation from the ocean was reduced, e.g. due to low sea surface temperatures. Within the restrictions of the conceptual model, we estimate q o c from present-day reanalysis data for four major monsoon systems, and demonstrate how this concept can help understand abrupt variations in monsoon strength on orbital timescales as found in proxy records.

Description: Assessing variable speed pump efficiency in water distribution systems Drinking Water Engineering and Science Discussions, 5, 47-65, 2012 Author(s): A. Marchi, A. R. Simpson, and N. Ertugrul Energy savings and greenhouse gas emission reductions are increasingly becoming important design targets in many industrial systems where fossil fuel based electrical energy is heavily utilised. In water distribution systems (WDSs) a significant portion of operational cost is related to pumping. Recent studies have considered variable speed pumps (VSPs) which aim to vary the operating point of the pump to match demand to pumping rate. Depending on the system characteristics, this approach can lead to considerable savings in operational costs. In particular, cost reductions can take advantage of the demand variability and can decrease energy consumption significantly. One of the issues in using variable speed pumping systems, however, is the total efficiency of the electric motor/pump arrangement under a given operating condition. This paper aims to provide a comprehensive discussion about the components of WDS that incorporate variable speed pumps (including electric motors, inverters and the pumps themselves) to provide an insight of ways of increasing the system efficiency and hence to reduce energy consumption. In addition, specific attention is given to selection of motor types, sizing, duty cycle of pump (ratio of on-time and time period), losses due to installation and motor faults. All these factors affect the efficiency of motor drive/pump system.

Description: Correcting the radar rainfall forcing of a hydrological model with data assimilation: application to flood forecasting in the Lez Catchment in Southern France Hydrology and Earth System Sciences Discussions, 9, 3527-3579, 2012 Author(s): E. Harader, V. Borrell Estupina, S. Ricci, M. Coustau, O. Thual, A. Piacentini, and C. Bouvier The present study explores the application of a data assimilation (DA) procedure to correct the radar rainfall inputs of an event-based, distributed, parsimonious hydrological model. A simplified Kalman filter algorithm was built on top of a rainfall-runoff model in order to assimilate discharge observations at the catchment outlet. The study site is the 114 km 2 Lez Catchment near Montpellier, France. This catchment is subject to heavy orographic rainfall and characterized by a karstic geology, leading to flash flooding events. The hydrological model uses a derived version of the SCS method, combined with a Lag and Route transfer function. Because it depends on geographical features and cloud structures, the radar rainfall input to the model is particularily uncertain and results in significant errors in the simulated discharges. The DA analysis was applied to estimate a constant correction to each event hyetogram. The analysis was carried out for 19 events, in two different modes: re-analysis and pseudo-forecast. In both cases, it was shown that the reduction of the uncertainty in the rainfall data leads to a reduction of the error in the simulated discharge. The resulting correction of the radar rainfall data was then compared to the mean field bias (MFB), a corrective coefficient determined using ground rainfall measurements, which are more accurate than radar but have a decreased spatial resolution. It was shown that the radar rainfall corrected using DA leads to improved discharge simulations and Nash criteria compared to the MFB correction.

Description: Numerical modelling of climate change impacts on freshwater lenses on the North Sea Island of Borkum Hydrology and Earth System Sciences Discussions, 9, 3473-3525, 2012 Author(s): H. Sulzbacher, H. Wiederhold, B. Siemon, M. Grinat, J. Igel, T. Burschil, T. Günther, and K. Hinsby A numerical variable-density groundwater model is set up for the North Sea Island of Borkum to estimate climate change impacts on coastal aquifers and especially the situation of barrier islands in the Wadden Sea. The database includes information from boreholes, a seismic survey, a helicopter-borne electromagnetic survey (HEM), monitoring of the freshwater-saltwater boundary by vertical electrode chains in two boreholes, measurements of groundwater table, pumping and slug tests, as well as water samples. Based on a statistical analysis of borehole columns, seismic sections and HEM, a hydrogeological model is set up. The groundwater model is developed using the finite-element programme FEFLOW. The variable-density groundwater model is calibrated on the basis of hydraulic, hydrological and geophysical data, in particular spatial HEM and local monitoring data. Verification runs with the calibrated model show good agreement between measured and computed hydraulic heads. A good agreement is also obtained between measured and computed density or total dissolved solids data for both the entire freshwater lens on a large scale and in the area of the well fields on a small scale. For simulating future changes in this coastal groundwater system until the end of the current century we use the climate scenario A2, specified by the Intergovernmental Panel on Climate Change and in particular the data for the German North Sea coast. Simulation runs show proceeding salinization with time beneath the well fields of the two waterworks Waterdelle and Ostland. The modelling study shows that spreading of well fields is an appropriate protection measure against excessive salinization of the water supply until the end of the current century.

Description: Isoprene emissions in Africa inferred from OMI observations of formaldehyde columns Atmospheric Chemistry and Physics Discussions, 12, 7475-7520, 2012 Author(s): E. A. Marais, D. J. Jacob, T. P. Kurosu, K. Chance, J. G. Murphy, C. Reeves, G. Mills, S. Casadio, D. B. Millet, M. P. Barkley, F. Paulot, and J. Mao We use 2005–2009 satellite observations of formaldehyde (HCHO) columns from OMI to infer biogenic isoprene emissions at monthly 1 × 1° resolution over the African continent. Our work includes new approaches to remove biomass burning influences using OMI absorbing aerosol optical depth data (to account for transport of fire plumes) and anthropogenic influences using AATSR satellite data for persistent small-flame fires (gas flaring). The resulting biogenic HCHO columns (Ω HCHO ) follow closely the distribution of vegetation patterns in Africa. We infer isoprene emission ( E ISOP ) from the local sensitivity S =ΔΩ HCHO /Δ E ISOP derived with the GEOS-Chem chemical transport model using two alternate isoprene oxidation mechanisms, and verify the validity of this approach using AMMA aircraft observations over West Africa and a longitudinal transect across central Africa. Displacement error (smearing) is diagnosed by anomalously high values of S and the corresponding data are removed. We find significant sensitivity of S to NO x under low-NO x conditions that we fit to a linear function of tropospheric column NO 2 from OMI. We estimate a 40% error in our inferred isoprene emissions under high-NO x conditions and 40–90% under low-NO x conditions. Comparison to the state-of-science MEGAN inventory indicates a large overestimate of central African rainforest emissions in that inventory.

Description: Polarization data from SCIAMACHY limb backscatter observations compared to vector radiative transfer model simulations Atmospheric Measurement Techniques Discussions, 5, 2221-2271, 2012 Author(s): P. Liebing, K. Bramstedt, S. Noël, V. Rozanov, H. Bovensmann, and J. P. Burrows SCIAMACHY is a passive imaging spectrometer onboard ENVISAT, designed to obtain trace gas abundances from measured radiances and irradiances in the UV to SWIR range in nadir, limb and occultation viewing modes. Its grating spectrometer introduces a substantial sensitivity to the polarization of the incoming light with nonnegligible effects on the radiometric calibration. To be able to correct for the polarization sensitivity, SCIAMACHY utilizes broadband Polarization Measurement Devices (PMDs). While for the nadir viewing mode the measured atmospheric polarization has been validated against POLDER data (Tilstra and Stammes, 2007, 2010), a similar validation study regarding the limb viewing mode has not yet been performed. This paper aims at an assessment of the quality of the SCIAMACHY limb polarization data. Since limb polarization measurements by other air- or spaceborne instruments in the spectral range of SCIAMACHY are not available, a comparison with radiative transfer simulations by SCIATRAN V3.1(Rozanov et al., 2012) using a wide range of atmospheric parameters is performed. SCIATRAN is a vector radiative transfer model (VRTM) capable of performing calculations of the multiply scattered radiance in a~spherically symmetric atmosphere. The study shows that the limb polarization data exhibit a large systematic bias which is decreasing with wavelength. The most likely reason for this bias is an instrumental phase shift which changes the relative contributions of different Stokes vector components to the PMD signal as compared to on-ground calibration measurements. It is also shown that it is in principle feasible to recalibrate the polarization sensitivity using the in-flight data and the VRTM simulations, enabling also the monitoring of its degradation. Together with an optimization of the algorithm used to calculate the in-flight polarization data an improved polarization correction can increase the radiometric accuracy of SCIAMACHY limb radiance spectra substantially.

Description: Ikaite crystals in melting sea ice – implications for p CO 2 and pH levels in Arctic surface waters The Cryosphere Discussions, 6, 1015-1035, 2012 Author(s): S. Rysgaard, R. N. Glud, K. Lennert, M. Cooper, N. Halden, R. J. G. Leakey, F. C. Hawthorne, and D. Barber A major issue of Arctic marine science is to understand whether the Arctic Ocean is, or will be, a source or sink for air-sea CO 2 exchange. This has been complicated by the recent discoveries of ikaite (CaCO 3 ·6H 2 O) in Arctic and Antarctic sea ice, which indicate that multiple chemical transformations occur in sea ice with a possible effect on CO 2 and pH conditions in surface waters. Here we report on biogeochemical conditions, microscopic examinations and x-ray diffraction analysis of single crystals from an actively melting 1.7 km 2 (0.5–1 m thick) drifting ice floe in the Fram Strait during summer. Our findings show that ikaite crystals are present throughout the sea ice but with larger crystals appearing in the upper ice layers. Ikaite crystals placed at elevated temperatures gradually disintegrated into smaller crystallites and dissolved. During our field campaign in late June, melt reduced the ice flow thickness by ca. 0.2 m per week and resulted in an estimated 1.6 ppm decrease of p CO 2 in the ocean surface mixed layer. This corresponds to an air-sea CO 2 uptake of 11 mmol m −2 sea ice d −1 or to 3.5 ton km −2 ice floe week −1 .

Description: Global distribution and climate forcing of marine organic aerosol – Part 2: Effects on cloud properties and radiative forcing Atmospheric Chemistry and Physics Discussions, 12, 7453-7474, 2012 Author(s): B. Gantt, J. Xu, N. Meskhidze, Y. Zhang, A. Nenes, S. J. Ghan, X. Liu, R. Easter, and R. Zaveri In the first part of this paper series (Meskhidze et al., 2011), a treatment of marine organic aerosols (including primary organic aerosol, secondary organic aerosols, and methane sulfonate) was implemented into the Community Atmosphere Model version 5 (CAM5) with a 7-mode Modal Aerosol Module. A series of simulations was conducted to quantify the changes in aerosol and cloud condensation nuclei concentrations in the marine boundary layer. In this study, changes in the cloud microphysical properties and radiative forcing resulting from marine organic aerosols are assessed. Model simulations show that the anthropogenic aerosol indirect forcing (AIF) predicted by CAM5 is decreased in absolute magnitude by up to ~0.10 W m −2 (8%) when marine organic aerosols are included. Changes in the AIF from marine organic aerosols are associated with small global increases in low-level in-cloud droplet number concentration and liquid water path of ~1.3 cm −3 (~1.6%) and 0.2 g m −2 (0.5%), respectively. Areas especially sensitive to changes in cloud properties due to marine organic aerosol include the Southern Ocean, North Pacific Ocean, and North Atlantic Ocean, all of which are characterized by high marine organic emission rates. As climate models are particularly sensitive to the background aerosol concentration, this small but non-negligible change in the AIF due to marine organic aerosols provides a notable link for ocean-ecosystem marine low-level cloud interactions and may be a candidate for consideration in future earth system models.

Description: Technical Note: Detection of gas bubble leakage via correlation of water column multibeam images Ocean Science, 8, 175-181, 2012 Author(s): J. Schneider von Deimling and C. Papenberg Hydroacoustic detection of natural gas release from the seafloor has been conducted in the past by using singlebeam echosounders. In contrast, modern multibeam swath mapping systems allow much wider coverage, higher resolution, and offer 3-D spatial correlation. Up to the present, the extremely high data rate hampers water column backscatter investigations and more sophisticated visualization and processing techniques are needed. Here, we present water column backscatter data acquired with a 50 kHz prototype multibeam system over a period of 75 seconds. Display types are of swath-images as well as of a "re-sorted" singlebeam presentation. Thus, individual and/or groups of gas bubbles rising from the 24 m deep seafloor clearly emerge in the acoustic images, making it possible to estimate rise velocities. A sophisticated processing scheme is introduced to identify those rising gas bubbles in the hydroacoustic data. We apply a cross-correlation technique adapted from particle imaging velocimetry (PIV) to the acoustic backscatter images. Temporal and spatial drift patterns of the bubbles are assessed and are shown to match very well to measured and theoretical rise patterns. The application of this processing to our field data gives clear results with respect to unambiguous bubble detection and remote bubble rise velocimetry. The method can identify and exclude the main source of misinterpretations, i.e. fish-mediated echoes. Although image-based cross-correlation techniques are well known in the field of fluid mechanics for high resolution and non-inversive current flow field analysis, we present the first application of this technique as an acoustic bubble detector.

Description: Accounting for seasonality in a soil moisture change detection algorithm for ASAR Wide Swath time series Hydrology and Earth System Sciences, 16, 773-786, 2012 Author(s): J. Van doninck, J. Peters, H. Lievens, B. De Baets, and N. E. C. Verhoest A change detection algorithm is applied on a three year time series of ASAR Wide Swath images in VV polarization over Calabria, Italy, in order to derive information on temporal soil moisture dynamics. The algorithm, adapted from an algorithm originally developed for ERS scatterometer, was validated using a simple hydrological model incorporating meteorological and pedological data. Strong positive correlations between modelled soil moisture and ASAR soil moisture were observed over arable land, while the correlation became much weaker over more vegetated areas. In a second phase, an attempt was made to incorporate seasonality in the different model parameters. It was observed that seasonally changing surface properties mainly affected the multitemporal incidence angle normalization. When applying a seasonal angular normalization, correlation coefficients between modelled soil moisture and retrieved soil moisture increased overall. Attempts to account for seasonality in the other model parameters did not result in an improved performance.

Description: Arctic surface temperatures from Metop AVHRR compared to in situ ocean and land data Ocean Science Discussions, 9, 1009-1043, 2012 Author(s): G. Dybkjær, R. Tonboe, and J. Høyer The ice surface temperature (IST) is an important boundary condition for both atmospheric and ocean and sea ice models and for coupled systems. An operational ice surface temperature product using satellite Metop AVHRR infra-red data was developed for MyOcean. The IST can be mapped in clear sky regions using a split window algorithm specially tuned for sea ice. Clear sky conditions are prevailing during spring in the Arctic while persistent cloud cover limits data coverage during summer. The cloud covered regions are detected using the EUMETSAT cloud mask. The Metop IST compares to 2 m temperature at the Greenland ice cap Summit within STD error of 3.14 °C and to Arctic drifting buoy temperature data within STD error of 3.69 °C. A case study reveal that the in situ radiometer data versus satellite IST STD error can be much lower (0.73 °C) and that the different in situ measures complicates the validation. Differences and variability between Metop IST and in situ data are analysed and discussed. An inter-comparison of Metop IST, numerical weather prediction temperatures and in situ observation indicates large biases between the different quantities. Because of the scarcity of conventional surface temperature or surface air temperature data in the Arctic the satellite IST data with its relatively good coverage can potentially add valuable information to model analysis for the Arctic atmosphere.

Description: Black Sea coastal forecasting system Ocean Science, 8, 183-196, 2012 Author(s): A. I. Kubryakov, G. K. Korotaev, V. L. Dorofeev, Y. B. Ratner, A. Palazov, N. Valchev, V. Malciu, R. Matescu, and T. Oguz The Black Sea coastal nowcasting and forecasting system was built within the framework of EU FP6 ECOOP (European COastalshelf sea OPerational observing and forecasting system) project for five regions: the south-western basin along the coasts of Bulgaria and Turkey, the north-western shelf along the Romanian and Ukrainian coasts, coastal zone around of the Crimea peninsula, the north-eastern Russian coastal zone and the coastal zone of Georgia. The system operates in the real-time mode during the ECOOP project and afterwards. The forecasts include temperature, salinity and current velocity fields. Ecosystem model operates in the off-line mode near the Crimea coast.

Description: Towards high resolution mapping of 3-D mesoscale dynamics from observations: preliminary comparison of retrieval techniques and models within MESCLA project Ocean Science Discussions, 9, 1045-1083, 2012 Author(s): B. Buongiorno Nardelli, S. Guinehut, A. Pascual, Y. Drillet, S. Ruiz, and S. Mulet Within the MyOcean R&D project MESCLA (MEsoSCale dynamical Analysis through combined model, satellite and in situ data), different estimates of the vertical velocities derived from observations have been compared. Two main approaches have been considered, one based on the retrieval of 3-D fields from the observations alone and one based on the analyses provided by MyOcean MERCATOR models. The motivation for this double approach is that, while data assimilation in numerical models is crucial to obtain more accurate analyses and forecasts, its results might be significantly influenced by specific model configurations (e.g. forcing, parameterization of smaller scale processes and spatial resolution). On the other hand, the purely observation-based approach is limited by the underlying assumptions of simplified dynamical models and by the relatively low resolution of present products. MESCLA tested innovative methods for the high resolution mapping of 3-D mesoscale dynamics from observations, developing new products that might be used to gradually build the next generations of operational observation-based products.

Description: Contribution of flowering trees to urban atmospheric biogenic volatile organic compound emissions Biogeosciences Discussions, 9, 3145-3172, 2012 Author(s): R. Baghi, D. Helmig, A. Guenther, T. Duhl, and R. Daly Emissions of biogenic volatile organic compounds (BVOC) from urban trees during and after blooming were measured during spring and early summer 2009 in Boulder, Colorado. Air samples were collected onto solid adsorbent cartridges from branch enclosures on the tree species crabapple, horse chestnut, honey locust, and hawthorn. These species constitute ~65 % of the insect-pollinated fraction of the flowering tree canopy (excluding catkin-producing trees) from the street area managed by the City of Boulder. Samples were analyzed for C 10 –C 15 BVOC by thermal desorption and gas chromatography coupled to a flame ionization detector and a mass spectrometer (GC/FID/MS). Identified emissions and emission rates from these four tree species during the flowering phase were found to vary over a wide range. Monoterpene emissions were identified for honey locust, horse chestnut and hawthorn. Sesquiterpene emissions were observed in horse chestnut and hawthorn samples. Crabapple flowers were found to emit significant amounts of benzyl alcohol and benzaldehyde. Floral BVOC emissions increased with temperature, generally exhibiting exponential temperature dependence. Changes in BVOC speciation during and after the flowering period were observed for every tree studied. Emission rates were significantly higher during the blooming compared to the vegetative state for crabapple and honey locust. Total normalized (30 °C) monoterpene emissions from honey locust were higher during flowering (5.26 μg Cg −1 h −1 ) than after flowering (1.23 μg Cg −1 h −1 ). The total normalized BVOC emission rate from crabapple (93 μg Cg −1 h −1 ) during the flowering period is of the same order as isoprene emissions from oak trees, which are among the highest BVOC emissions observed from plants to date. These findings illustrate that during the relatively brief springtime flowering period, floral emissions constitute by far the most significant contribution to the BVOC flux from these tree species, some of which are leafless at this time. Experimental results were integrated into the MEGAN biogenic emission model and simulations were performed to estimate the contribution of floral BVOC emissions to the total urban BVOC flux during the spring flowering period. The floral BVOC emitted during this three-month simulation are equivalent to 11 % of the cumulative monoterpene flux for the Boulder urban area.

Description: Rockfall hazard and risk assessments along roads at a regional scale: example in Swiss Alps Natural Hazards and Earth System Science, 12, 615-629, 2012 Author(s): C. Michoud, M.-H. Derron, P. Horton, M. Jaboyedoff, F.-J. Baillifard, A. Loye, P. Nicolet, A. Pedrazzini, and A. Queyrel Unlike fragmental rockfall runout assessments, there are only few robust methods to quantify rock-mass-failure susceptibilities at regional scale. A detailed slope angle analysis of recent Digital Elevation Models (DEM) can be used to detect potential rockfall source areas, thanks to the Slope Angle Distribution procedure. However, this method does not provide any information on block-release frequencies inside identified areas. The present paper adds to the Slope Angle Distribution of cliffs unit its normalized cumulative distribution function. This improvement is assimilated to a quantitative weighting of slope angles, introducing rock-mass-failure susceptibilities inside rockfall source areas previously detected. Then rockfall runout assessment is performed using the GIS- and process-based software Flow-R, providing relative frequencies for runout. Thus, taking into consideration both susceptibility results, this approach can be used to establish, after calibration, hazard and risk maps at regional scale. As an example, a risk analysis of vehicle traffic exposed to rockfalls is performed along the main roads of the Swiss alpine valley of Bagnes.

Description: Evolution of skewness and kurtosis of weakly nonlinear unidirectional waves over a sloping bottom Natural Hazards and Earth System Science, 12, 631-638, 2012 Author(s): H. Zeng and K. Trulsen We consider the effect of slowly varying depth on the values of skewness and kurtosis of weakly nonlinear irregular waves propagating from deeper to shallower water. It is known that the equilibrium value of kurtosis decreases with decreasing depth for waves propagating on constant depth. Waves propagating over a sloping bottom must continually adjust toward a new equilibrium state. We demonstrate that weakly nonlinear waves may need a considerable horizontal propagation distance in order to adjust to a new shallower environment, therefore the kurtosis can be notably different from the equilibrium value for each corresponding depth both on top of and beyond a bottom slope. A change of depth can provoke a wake-like spatially non-uniform distribution of kurtosis on the lee side of the slope. As an application, we anticipate that the probability of freak waves on or near the edge of the continental shelf may exhibit a rather complicated spatial structure for wave fields entering from deep sea.

Description: Analysis of ΔO 2 /ΔCO 2 ratios for the pollution events observed at Hateruma Island, Japan Atmospheric Chemistry and Physics, 12, 2713-2723, 2012 Author(s): C. Minejima, M. Kubo, Y. Tohjima, H. Yamagishi, Y. Koyama, S. Maksyutov, K. Kita, and H. Mukai Pollution events extracted from the in situ observations of atmospheric CO 2 and O 2 mixing ratios at Hateruma Island (HAT, 24° N, 124° E) during the period from October 2006 and December 2008 are examined. The air mass origins for the pollution events are categorized by using back trajectory analysis, and the oxidative ratios (OR = −O 2 :CO 2 molar exchange ratio) for selected pollution events are calculated. We find that there is a significant difference in the average oxidative ratios between events from China (OR = 1.14 ± 0.12, n = 25) and Japan/Korea (OR = 1.37 ± 0.15, n = 16). These values are in a good agreement with the national average oxidative ratios for the emissions from fossil fuel burning and cement production (FFBC) in China (OR FFBC = 1.11 ± 0.03) and Korea/Japan (OR FFBC = 1.36 ± 0.02). Compared with the observation, simulations of the atmospheric O 2 and CO 2 mixing ratios using Lagrangian particle dispersion models do a good job in reconstructing the average oxidative ratio of the pollution events originating in China but tend to underestimate for events originating in Japan/Korea. A sensitivity test suggests that the simulated atmospheric oxidative ratios at HAT are especially sensitive to changes in Chinese fuel mix.

Description: Carbonaceous aerosols in China: top-down constraints on primary sources and estimation of secondary contribution Atmospheric Chemistry and Physics, 12, 2725-2746, 2012 Author(s): T.-M. Fu, J. J. Cao, X. Y. Zhang, S. C. Lee, Q. Zhang, Y. M. Han, W. J. Qu, Z. Han, R. Zhang, Y. X. Wang, D. Chen, and D. K. Henze We simulated elemental carbon (EC) and organic carbon (OC) aerosols in China and compared model results to surface measurements at Chinese rural and background sites, with the goal of deriving "top-down" emission estimates of EC and OC, as well as better quantifying the secondary sources of OC. We included in the model state-of-the-science Chinese "bottom-up" emission inventories for EC (1.92 TgC yr −1 ) and OC (3.95 TgC yr −1 ), as well as updated secondary OC formation pathways. The average simulated annual mean EC concentration at rural and background sites was 1.1 μgC m −3 , 56% lower than the observed 2.5 μgC m −3 . The average simulated annual mean OC concentration at rural and background sites was 3.4 μgC m −3 , 76% lower than the observed 14 μgC m −3 . Multiple regression to fit surface monthly mean EC observations at rural and background sites yielded the best estimate of Chinese EC source of 3.05 ± 0.78 TgC yr −1 . Based on the top-down EC emission estimate and observed seasonal primary OC/EC ratios, we estimated Chinese OC emissions to be 6.67 ± 1.30 TgC yr −1 . Using these top-down estimates, the simulated average annual mean EC concentration at rural and background sites was significantly improved to 1.9 μgC m −3 . However, the model still significantly underestimated observed OC in all seasons (simulated average annual mean OC at rural and background sites was 5.4 μgC m −3 ), with little skill in capturing the spatiotemporal variability. Secondary formation accounts for 21% of Chinese annual mean surface OC in the model, with isoprene being the most important precursor. In summer, as high as 62% of the observed surface OC may be due to secondary formation in eastern China. Our analysis points to four shortcomings in the current bottom-up inventories of Chinese carbonaceous aerosols: (1) the anthropogenic source is underestimated on a national scale, particularly for OC; (2) the spatiotemporal distributions of emissions are misrepresented; (3) there is a missing source in western China, likely associated with the use of biofuels or other low-quality fuels for heating; and (4) sources in fall are not well represented, either because the seasonal shifting of emissions and/or secondary formation are poorly captured or because specific fall emission events are missing. In addition, secondary production of OC in China is severely underestimated. More regional measurements with better spatiotemporal coverage are needed to resolve these shortcomings.

Description: Corrigendum to "Impact of rainfall spatial distribution on rainfall-runoff modelling efficiency and initial soil moisture conditions estimation" published in Nat. Hazards Earth Syst. Sci., 11, 157–170, 2011 Natural Hazards and Earth System Science, 12, 267-267, 2012 Author(s): Y. Tramblay, C. Bouvier, P.-A. Ayral, and A. Marchandise No abstract available.

Description: On the Shelf Resonances of the Gulf of Carpentaria and the Arafura Sea Ocean Science Discussions, 9, 443-497, 2012 Author(s): D. J. Webb A numerical model is used to investigate the resonances of the Gulf of Carpentaria and the Arafura Sea. The model is forced at the shelf edge, first with physically realistic real values of angular velocity. The response functions at points within the region show maxima and other behaviour which imply that resonances are involved but it is difficult to be more specific. The study is then extended to complex angular velocities and the results then show a clear pattern of gravity wave and Rossby wave like resonances. The properties of the resonances are investigated and used to reinterpret the responses at real values of angular velocity. It is found that in some regions the response is dominated by modes trapped between the shelf edge and the coast or between opposing coastlines. In other regions the resonances show cooperative behaviour, possibly indicating the importance of other physical processes.

Description: Bromine and iodine chemistry in a global chemistry-climate model: description and evaluation of very short-lived oceanic sources Atmospheric Chemistry and Physics, 12, 1423-1447, 2012 Author(s): C. Ordóñez, J.-F. Lamarque, S. Tilmes, D. E. Kinnison, E. L. Atlas, D. R. Blake, G. Sousa Santos, G. Brasseur, and A. Saiz-Lopez The global chemistry-climate model CAM-Chem has been extended to incorporate an expanded bromine and iodine chemistry scheme that includes natural oceanic sources of very short-lived (VSL) halocarbons, gas-phase photochemistry and heterogeneous reactions on aerosols. Ocean emissions of five VSL bromocarbons (CHBr 3 , CH 2 Br 2 , CH 2 BrCl, CHBrCl 2 , CHBr 2 Cl) and three VSL iodocarbons (CH 2 ICl, CH 2 IBr, CH 2 I 2 ) have been parameterised by a biogenic chlorophyll- a (chl- a ) dependent source in the tropical oceans (20° N–20° S). Constant oceanic fluxes with 2.5 coast-to-ocean emission ratios are separately imposed on four different latitudinal bands in the extratropics (20°–50° and above 50° in both hemispheres). Top-down emission estimates of bromocarbons have been derived using available measurements in the troposphere and lower stratosphere, while iodocarbons have been constrained with observations in the marine boundary layer (MBL). Emissions of CH 3 I are based on a previous inventory and the longer lived CH 3 Br is set to a surface mixing ratio boundary condition. The global oceanic emissions estimated for the most abundant VSL bromocarbons – 533 Gg yr −1 for CHBr 3 and 67.3 Gg yr −1 for CH 2 Br 2 – are within the range of previous estimates. Overall the latitudinal and vertical distributions of modelled bromocarbons are in good agreement with observations. Nevertheless, we identify some issues such as the reduced number of aircraft observations to validate models in the Southern Hemisphere, the overestimation of CH 2 Br 2 in the upper troposphere – lower stratosphere and the underestimation of CH 3 I in the same region. Despite the difficulties involved in the global modelling of the shortest lived iodocarbons (CH 2 ICl, CH 2 IBr, CH 2 I 2 ), modelled results are in good agreement with published observations in the MBL. Finally, sensitivity simulations show that knowledge of the diurnal emission cycle for these species, in particular for CH 2 I 2 , is key to assess their global source strength.

Description: Contributions of ectomycorrhizal fungal mats to forest soil respiration Biogeosciences Discussions, 9, 1635-1666, 2012 Author(s): C. L. Phillips, L. A. Kluber, J. P. Martin, B. A. Caldwell, and B. J. Bond Distinct aggregations of fungal hyphae and rhizomorphs, or "mats" formed by some genera of ectomycorrhizal (EcM) fungi are common features of soils in coniferous forests of the Pacific Northwest. We measured in situ respiration rates of Piloderma mats and neighboring non-mat soils in an old-growth Douglas-fir forest in Western Oregon to investigate whether there was an incremental increase in respiration from mat soils, and to estimate mat contributions to total soil respiration. We found that areas where Piloderma mats colonized the organic horizon often had higher soil surface flux than non-mats, with the incremental increase in respiration averaging 16 % across two growing seasons. Both soil physical factors and biochemistry were related to the higher surface flux of mat soils. When air-filled pore space was low (high soil moisture), soil CO 2 production was concentrated into near-surface soil horizons where mats tend to colonize, resulting in greater apparent differences in respiration between mat and non-mat soils. Respiration rates were also correlated with the activity of chitin-degrading soil enzymes. This suggests that the elevated activity of fungal mats may be related to consumption or turnover of chitinous fungal cell-wall materials. We found Piloderma mats present across 57 % of the soil surface in the study area, and use this value to estimate a respiratory contribution from mats at the stand-scale of about 9 % of total soil respiration. The activity of EcM mats, which includes both EcM fungi and microbial associates, was estimated to constitute a substantial portion of total soil respiration in this old-growth Douglas-fir forest.

Description: Ice nuclei in marine air: bioparticles or dust? Atmospheric Chemistry and Physics Discussions, 12, 4373-4416, 2012 Author(s): S. M. Burrows, C. Hoose, U. Pöschl, and M. G. Lawrence Ice nuclei can influence the properties of clouds and precipitation, but their sources and distribution in the atmosphere are still not well known. Particularly little attention has been paid to IN sources in marine environments, although anecdotal evidence suggests that IN populations in remote marine regions may be dominated by biological particles associated with sea spray. In this exploratory model study, we aim to bring attention to this long-neglected topic and identify promising target regions for future field campaigns. We assess the likely global distribution of marine biological ice nuclei using a combination of historical observations, satellite data and model output. By comparing simulated marine biological IN distributions and dust IN distributions, we predict strong regional differences in the importance of marine biological IN relative to dust IN. Our analysis suggests that marine biological IN are most likely to play a dominant role in determining IN concentrations over the Southern Ocean, so future field campaigns aimed at investigating marine biological IN should target that region. Climate-related changes in the abundance and emission of biological marine IN could affect marine cloud properties, thereby introducing previously unconsidered feedbacks that influence the hydrological cycle and the Earth's energy balance. Furthermore, marine biological IN may be an important aspect to consider in proposals for marine cloud brightening by artificial sea spray production.

Description: An observation-based approach to identify local natural dust events from routine aerosol ground monitoring Atmospheric Chemistry and Physics Discussions, 12, 4279-4310, 2012 Author(s): D. Q. Tong, M. Dan, T. Wang, and P. Lee Dust is a major component of atmospheric aerosols in many parts of the world. Although there exist many routine aerosol monitoring networks, it is often difficult to obtain dust records from these networks, because these monitors are either deployed far away from dust active regions (most likely collocated with dense population) or contaminated by anthropogenic sources and other natural sources, such as wildfires and vegetation detritus. Here we propose a new approach to identify local dust events relying solely on aerosol mass and composition from general-purpose aerosol measurements. Through analyzing the chemical and physical characteristics of aerosol observations during satellite-detected dust episodes, we select five indicators to be used to identify local dust records: (1) high PM 10 concentrations; (2) low PM 2.5 /PM 10 ratio; (3) higher concentrations and percentage of crustal elements; (4) lower percentage of anthropogenic pollutants; and (5) low enrichment factors of anthropogenic elements. After establishing these identification criteria, we conduct hierarchical cluster analysis for all validated aerosol measurement data over 68 IMPROVE sites in the Western United States. A total of 182 local dust events were identified over 30 of the 68 locations from 2000 to 2007. These locations are either close to the four US Deserts, namely the Great Basin Desert, the Mojave Desert, the Sonoran Desert, and the Chihuahuan Desert, or in the high wind power region (Colorado). During the eight-year study period, the total number of dust events displays an interesting four-year activity cycle (one in 2000–2003 and the other in 2004–2007). The years of 2003, 2002 and 2007 are the three most active dust periods, with 46, 31 and 24 recorded dust events, respectively, while the years of 2000, 2004 and 2005 are the calmest periods, all with single digit dust records. Among these deserts, the Chihuahua Desert (59 cases) and the Sonoran Desert (62 cases) are by far the most active source regions. In general, the Chihuahua Desert dominates dust activities in the first half of the eight-year period while the Sonoran Desert in the second half. The monthly frequency of dust events shows a peak from March to July and a second peak in autumn from September to November. The large quantity of dust events occurring in summertime also suggests the prevailing impact of windblown dust across the year. This seasonal variation is consistent with previous model simulations over the United States.

Description: Quantifying retrieval uncertainties in the CM-SAF cloud physical property algorithm with simulated SEVIRI observations Atmospheric Chemistry and Physics Discussions, 12, 4311-4340, 2012 Author(s): B. J. Jonkheid, R. A. Roebeling, and E. van Meijgaard The uncertainties in the cloud physical properties derived from satellite observations make it difficult to interpret model evaluation studies. In this paper, the uncertainties in the cloud water path (CWP) retrievals derived with the cloud physical properties retrieval algorithm (CPP) of the climate monitoring satellite application facility (CM-SAF) are investigated. To this end, a numerical simulator of MSG-SEVIRI observations was developed that calculates the reflectances at 0.64 and 1.63 μm for a wide range of cloud parameters, satellite viewing geometries and surface albedos. These reflectances are used as input to CPP, and the retrieved values of CWP are compared to the original input of the simulator. It is shown that the CWP retrievals are very sensitive to the assumptions made in the CPP code. The CWP retrieval errors are generally small for unbroken single-phase clouds with COT 〉10, with retrieval errors of ~3% for liquid water clouds to ~10% for ice clouds. When both liquid water and ice clouds are present in a pixel, the CWP retrieval errors increase dramatically; depending on the cloud, this can lead to uncertainties of 40–80%. CWP retrievals also become more uncertain when the cloud does not cover the entire pixel, leading to errors of ~50% for cloud fractions of 0.75 and even larger errors for smaller cloud fractions. Thus, the satellite retrieval of cloud physical properties of broken clouds and multi-phase clouds is complicated by inherent difficulties, and the proper interpretation of such retrievals requires extra care.

Description: Physically-based modeling of topographic effects on spatial evapotranspiration and soil moisture patterns through radiation and wind Hydrology and Earth System Sciences, 16, 357-373, 2012 Author(s): M. Liu, A. Bárdossy, J. Li, and Y. Jiang In this paper, simulations with the Soil Water Atmosphere Plant (SWAP) model are performed to quantify the spatial variability of both potential and actual evapotranspiration (ET), and soil moisture content (SMC) caused by topography-induced spatial wind and radiation differences. To obtain the spatially distributed ET/SMC patterns, the field scale SWAP model is applied in a distributed way for both pointwise and catchment wide simulations. An adapted radiation model from r.sun and the physically-based meso-scale wind model METRAS PC are applied to obtain the spatial radiation and wind patterns respectively, which show significant spatial variation and correlation with aspect and elevation respectively. Such topographic dependences and spatial variations further propagate to ET/SMC. A strong spatial, seasonal-dependent, scale-relevant intra-catchment variability in daily/annual ET and less variability in SMC can be observed from the numerical experiments. The study concludes that topography has a significant effect on ET/SMC in the humid region where ET is a energy limited rather than water availability limited process. It affects the spatial runoff generation through spatial radiation and wind, therefore should be applied to inform hydrological model development. In addition, the methodology used in the study can serve as a general method for physically-based ET estimation for data sparse regions.

Description: Enhanced cold-season warming in semi-arid regions Atmospheric Chemistry and Physics Discussions, 12, 4627-4653, 2012 Author(s): J. Huang, X. Guan, and F. Ji This study examined surface air temperature trends over global land from 1901–2009. It is found that the warming trend was particularly enhanced, in the boreal cold season (November to March) over semi-arid regions (with precipitation of 200–600 mm yr −1 ), showing a temperature increase of 1.53 °C as compared to the global annual mean temperature increase of 1.13 °C over land. In mid-latitude semi-arid areas of Europe, Asia, and North America, temperatures in the cold season increased by 1.41, 2.42, and 1.5 °C, respectively. The semi-arid regions contribute 44.46% to global annual-mean land-surface temperature trend. The mid-latitude semi-arid regions in the Northern Hemisphere accounting contribute by 27.0% of the total, with the mid-latitude semi-arid areas in Europe, Asia, and North America accounting for 6.29%, 13.81%, and 6.85%, respectively. Such enhanced semi-arid warming (ESAW) may cause these regions to become drier and warmer.

Description: Humidity-dependent phase state of SOA particles from biogenic and anthropogenic precursors Atmospheric Chemistry and Physics Discussions, 12, 4447-4476, 2012 Author(s): E. Saukko, A. T. Lambe, P. Massoli, Koop, T., J. P. Wright, D. R. Croasdale, D. A. Pedernera, T. B. Onasch, A. Laaksonen, P. Davidovits, D. R. Worsnop, and A. Virtanen The physical phase state (solid, semi-solid, or liquid) of secondary organic aerosol (SOA) particles has important implications for a number of atmospheric processes. We report the phase state of SOA particles spanning a wide range of oxygen to carbon ratios (O/C), used here as a surrogate for SOA oxidation level, produced in a flow tube reactor by photo-oxidation of various atmospherically relevant surrogate anthropogenic and biogenic volatile organic compounds (VOCs). The phase state of laboratory-generated SOA was determined by the particle bounce behavior after inertial impaction on a polished steel substrate. The measured bounce fraction was evaluated as a function of relative humidity and SOA oxidation level (O/C) measured by an Aerodyne high resolution time of flight aerosol mass spectrometer (HR-ToF AMS). The main findings of the study are: (1) Biogenic and anthropogenic SOA particles are found to be solid or semi-solid until a relative humidity of at least 50 % RH at impaction is reached. (2) Long-chain alkanes produce liquid SOA particles when generated at low oxidation level of O/C

Description: Carbonaceous aerosol AAE inferred from in-situ aerosol measurements at the Gosan ABC super site, and the implications for brown carbon aerosol Atmospheric Chemistry and Physics Discussions, 12, 4507-4539, 2012 Author(s): C. E. Chung, S.-W. Kim, M. Lee, S.-C. Yoon, and S. Lee Carbon mass of aerosols and its division between EC and OC sources were continuously measured at hourly intervals from October 2009 to June 2010. During this 9-month period, we also measured the aerosol absorption coefficient at 7 wavelengths and obtained PM mass density data at 1-h resolution. The measurement was made at the Gosan ABC super site, which is an ideal location for monitoring long-range transported aerosols from China. We remove the absorption data with significant dust influence using the mass ratio of PM 10 to PM 2.5 . The remaining data shows an Absorption Ångström Exponent (AAE) of about 1.27, which we suggest represent the average carbonaceous aerosol (CA) AAE at Gosan. CA AAE is highest in winter, in which the monthly value is near 1.4. We find a positive correlation between the mass ratio of OC to EC and CA AAE, and successfully increase the correlation by filtering out data associated with weak absorption signal. After the filtering, absorption coefficient is regressed on OC and EC mass densities. Black carbon (BC) and organic aerosol (OA) absorption cross sections per carbon mass are found to be 5.1 (4.2–6.0) and 1.4 (1.1–1.8) m 2 g −1 at 520 nm respectively. From the estimated BC & OA MAC, we find that OA contributes about 45% to CA absorption at 520 nm. OA AAE is found to be 1.7 (1.4–2.1). Compared with a previous estimate of OA MAC and AAE, our estimates at Gosan strongly suggest that the strongly-absorbing so-called brown carbon spheres are either unrelated to biomass burning or absent near the emission source.

Description: The importance of parameter resampling for soil moisture data assimilation into hydrologic models using the particle filter Hydrology and Earth System Sciences, 16, 375-390, 2012 Author(s): D. A. Plaza, R. De Keyser, G. J. M. De Lannoy, L. Giustarini, P. Matgen, and V. R. N. Pauwels The Sequential Importance Sampling with Resampling (SISR) particle filter and the SISR with parameter resampling particle filter (SISR-PR) are evaluated for their performance in soil moisture assimilation and the consequent effect on baseflow generation. With respect to the resulting soil moisture time series, both filters perform appropriately. However, the SISR filter has a negative effect on the baseflow due to inconsistency between the parameter values and the states after the assimilation. In order to overcome this inconsistency, parameter resampling is applied along with the SISR filter, to obtain consistent parameter values with the analyzed soil moisture state. Extreme parameter replication, which could lead to a particle collapse, is avoided by the perturbation of the parameters with white noise. Both the modeled soil moisture and baseflow are improved if the complementary parameter resampling is applied. The SISR filter with parameter resampling offers an efficient way to deal with biased observations. The robustness of the methodology is evaluated for 3 model parameter sets and 3 assimilation frequencies. Overall, the results in this paper indicate that the particle filter is a promising tool for hydrologic modeling purposes, but that an additional parameter resampling may be necessary to consistently update all state variables and fluxes within the model.

Description: Organic molecular markers and signature from wood combustion particles in winter ambient aerosols: aerosol mass spectrometer (AMS) and high time-resolved GC-MS measurements in Augsburg, Germany Atmospheric Chemistry and Physics Discussions, 12, 4831-4866, 2012 Author(s): M. Elsasser, M. Crippa, J. Orasche, P. F. DeCarlo, M. Oster, M. Pitz, T. L. Gustafson, J. B. C. Pettersson, J. Schnelle-Kreis, A. S. H. Prévôt, and R. Zimmermann The impact of wood combustion on ambient aerosols was investigated in Augsburg, Germany during a winter measurement campaign of a six-week period. Special attention was paid to the high time resolution observations of wood combustion with different mass spectrometric methods. Here we present and compare the results from an Aerodyne aerosol mass spectrometer (AMS) and gas chromatographic – mass spectrometric (GC-MS) analysed PM 1 filters on an hourly basis. This includes source apportionment of the AMS derived organic mass by using positive matrix factorisation (PMF) and analysis of levoglucosan as wood combustion marker, respectively. In the measurement period nitrate and organics are the main contributors to the defined submicron particle mass with 28% and 35%, respectively. To the latter wood combustion organic aerosol (WCOA) contributes 23% on average and 27% in the evening and night-time. Conclusively, wood combustion has a strong influence on the organics and overall aerosol composition. Levoglucosan accounts for 14% of WCOA mass with a higher percentage in comparison to other studies. The ratio between the mass of levoglucosan and organic carbon amounts to 0.06. This study is unique in the one-hour time resolution comparison between the wood combustion results of the AMS and the GC-MS analysed filter method at a PM 1 particle size range. This comparison of the concentration courses of the PMF WCOA factor, levoglucosan estimated by the AMS data and the levoglucosan measured by GC-MS is highly correlated, and a detailed discussion on the contributors to the wood combustion marker ion at mass-to-charge ratio 60 will be given. This offers a suitable application possibility for the description of the wood combustion course by the WCOA factor and the levoglucosan concentration estimated by AMS data. However, quantitative description of the levoglucosan concentration estimated by the AMS data is difficult due to the offset of latter compared to measured levoglucosan by the GC-MS.

Description: Mean winds, temperatures and the 16- and 5-day planetary waves in the mesosphere and lower thermosphere over Bear Lake Observatory (42° N, 111° W) Atmospheric Chemistry and Physics, 12, 1571-1585, 2012 Author(s): K. A. Day, M. J. Taylor, and N. J. Mitchell Atmospheric temperatures and winds in the mesosphere and lower thermosphere have been measured simultaneously using the Aura satellite and a meteor radar at Bear Lake Observatory (42° N, 111° W), respectively. The data presented in this study is from the interval March 2008 to July 2011. The mean winds observed in the summer-time over Bear Lake Observatory show the meridional winds to be equatorward at meteor heights during April−August and to reach monthly-mean velocities of −12 m s −1 . The mean winds are closely related to temperatures in this region of the atmosphere and in the summer the coldest mesospheric temperatures occur about the same time as the strongest equatorward meridional winds. The zonal winds are eastward through most of the year and in the summer strong eastward zonal wind shears of up to ~4.5 m s −1 km −1 are present. However, westward winds are observed at the upper heights in winter and sometimes during the equinoxes. Considerable inter-annual variability is observed in the mean winds and temperatures. Comparisons of the observed winds with URAP and HWM-07 reveal some large differences. Our radar zonal wind observations are generally more eastward than predicted by the URAP model zonal winds. Considering the radar meridional winds, in comparison to HWM-07 our observations reveal equatorward flow at all meteor heights in the summer whereas HWM-07 suggests that only weakly equatorward, or even poleward flows occur at the lower heights. However, the zonal winds observed by the radar and modelled by HWM-07 are generally similar in structure and strength. Signatures of the 16- and 5-day planetary waves are clearly evident in both the radar-wind data and Aura-temperature data. Short-lived wave events can reach large amplitudes of up to ~15 m s −1 and 8 K and 20 m s −1 and 10 K for the 16- and 5-day waves, respectively. A clear seasonal and short-term variability are observed in the 16- and 5-day planetary wave amplitudes. The 16-day wave reaches largest amplitude in winter and is also present in summer, but with smaller amplitudes. The 5-day wave reaches largest amplitude in winter and in late summer. An inter-annual variability in the amplitude of the planetary waves is evident in the four years of observations. Some 41 episodes of large-amplitude wave occurrence are identified. Temperature and wind amplitudes for these episodes, A T and A W , that passed the Student T-test were found to be related by, A T = 0.34 A W and A T = 0.62 A W for the 16- and 5-day wave, respectively.

Description: Remote sensing-based estimation of gross primary production in a subalpine grassland Biogeosciences Discussions, 9, 1711-1758, 2012 Author(s): M. Rossini, S. Cogliati, M. Meroni, M. Migliavacca, M. Galvagno, L. Busetto, E. Cremonese, T. Julitta, C. Siniscalco, U. Morra di Cella, and R. Colombo This study investigates the performances in a terrestrial ecosystem of gross primary production (GPP) estimation of a suite of spectral vegetation indexes (VIs) that can be computed from currently orbiting platforms. Vegetation indexes were computed from near-surface field spectroscopy measurements collected using an automatic system designed for high temporal frequency acquisition of spectral measurements in the visible near-infrared region. Spectral observations were collected for two consecutive years in Italy in a subalpine grassland equipped with an Eddy Covariance (EC) flux tower which provides continuous measurements of net ecosystem carbon dioxide (CO 2 ) exchange (NEE) and the derived GPP. Different VIs were calculated based on ESA-MERIS and NASA-MODIS spectral bands and correlated with biophysical (Leaf Area Index, LAI; fraction of photosynthetically active radiation intercepted by green vegetation, f IPAR g ), biochemical (chlorophyll concentration) and ecophysiological (green light-use efficiency, LUE g ) canopy variables. In this study, the normalized difference vegetation index (NDVI) showed better correlations with LAI and f PAR g ( r = 0.90 and 0.95, respectively), the MERIS terrestrial chlorophyll index (MTCI) with leaf chlorophyll content ( r = 0.91) and the Photochemical Reflectance Index (PRI 551 ), computed as ( R 531 − R 551 )/( R 531 + R 551 ) with LUE g ( r = 0.64). Subsequently, these VIs were used to estimate GPP using different modelling solutions based on the light-use efficiency model describing the GPP as driven by the photosynthetically active radiation absorbed by green vegetation (APAR g ) and by the efficiency (ε) with which plants use the absorbed radiation to fix carbon via photosynthesis. Results show that GPP can be successfully modelled with a combination of VIs and meteorological data or VIs only. Vegetation indexes designed to be more sensitive to chlorophyll content explained most of the variability in GPP in the ecosystem investigated, characterized by a strong seasonal dynamic of GPP. Accuracy in GPP estimation slightly improves when taking into account high frequency modulations of GPP driven by incident PAR or modelling LUE g with the PRI in model formulation. Similar results were obtained for both measured daily VIs and VIs obtained as 16-day composite time series and then downscaled from the compositing period to daily scale (resampled data). However, the use of resampled data rather than measured daily input data decreases the accuracy of the total GPP estimation on an annual basis.

Description: Soil organic carbon storage changes in coastal wetlands of the modern Yellow River Delta from 2000 to 2009 Biogeosciences Discussions, 9, 1759-1779, 2012 Author(s): J. Yu, Y. Wang, Y. Li, H. Dong, D. Zhou, G. Han, H. Wu, G. Wang, P. Mao, and Y. Gao Soil carbon sequestration plays an essential role in mitigating CO 2 increases and the subsequently global greenhouse effect. The storages and dynamics of soil organic carbon (SOC) of 0–30 cm soil depth in different landscape types including beaches, reservoir and pond, reed wetland, forest wetland, bush wetland, farmland, building land, bare land (severe saline land) and salt field in the modern Yellow River Delta (YRD), were studied based on the data of the regional survey and laboratory analysis. The landscape types were classified by the interpretation of remote sensing images of 2000 and 2009, which was calibrated by field survey results. The results revealed an increase of 10.59 km 2 in the modem YRD area from 2000 to 2009. The SOC density varied ranging from 0.73 kg m −2 to 21.60 kg m −2 at depth of 30 cm. There were ~3.97 × 10 6 t and 3.98 × 10 6 t SOC stored in the YRD in 2000 and 2009, respectively. The SOC storages changed greatly in beaches, bush wetland, farm land and salt field which were affected dominantly by anthropogenic activities. The area of the YRD increased greatly within 10 yr, however, the small increase of SOC storage in the region was observed due to landscape changes, indicating that the modern YRD was a potential carbon sink and anthropogenic activity was a key factor for SOC change.

Description: Evolution of marine storminess in the Belgian part of the North Sea Natural Hazards and Earth System Science, 12, 305-312, 2012 Author(s): D. Van den Eynde, R. De Sutter, and P. Haerens Severe storms have affected European coast lines in the past but knowledge on changes in storminess for the last decades is still sparse. Climate change is assumed to be a main driving factor with the potential to induce changes on the intensity, duration and frequency of powerful marine storms, including a long-term influence on peak wind speeds, surges and waves. It is, therefore, important to investigate whether in the last decades changes in the magnitude of storms, their duration and frequency could be observed. Understanding trends in storminess in the last decades will help to better prepare coastal managers for future events, taking into account potential changes on storm occurrence and magnitude to improve planning of mitigation and adaptation strategies. The purpose of this study was to focus on the evolution of extreme wind conditions, wave height and storm surge levels in the North Sea Region, especially in the Belgian part of the North Sea (BPNS). Based on the analysis performed it is concluded that no clear trend can be observed for the occurrence of significant increasing extreme wind speeds over the BPNS. Furthermore, one can conclude that not enough scientific evidence is available to support scenarios with increased wave height or storminess.

Description: Inferring snow pack ripening and melt out from distributed ground surface temperature measurements The Cryosphere Discussions, 6, 563-591, 2012 Author(s): M.-O. Schmid, S. Gubler, J. Fiddes, and S. Gruber The seasonal snow cover and its melting are heterogeneous both in space and time. Describing and modelling this variability are important because it affects divers phenomena such as runoff, ground temperatures or slope movements. This study investigates the derivation of melting characteristics based on spatial clusters of temperature measurements. Results are based on data from Switzerland where ground surface temperatures were measured with miniature loggers (iButtons) at 40 locations, referred to as footprints. At each footprint, ten iButtons have been distributed randomly few cm below the ground surface over an area of 10 m × 10 m. Footprints span elevations of 2100–3300 m a.s.l. and slope angles of 0–55°, as well as diverse slope expositions and types of surface cover and ground material. Based on two years of temperature data, the basal ripening date and the melt-out date are determined for each iButton, aggregated to the footprint level and further analysed. The date of melt out could be derived for nearly all iButtons, the ripening date could be extracted for only approximately half of them because it requires ground freezing below the snow pack. The variability within a footprint is often considerable and one to three weeks difference between melting or ripening of the points in one footprint is not uncommon. The correlation of mean annual ground surface temperatures, ripening date and melt-out date is moderate, making them useful intuitive complementary measured for model evaluation.

Description: An isotope view on ionising radiation as a source of sulphuric acid Atmospheric Chemistry and Physics Discussions, 12, 5039-5064, 2012 Author(s): M. B. Enghoff, N. Bork, S. Hattori, C. Meusinger, M. Nakagawa, J. O. P. Pedersen, S. Danielache, Y. Ueno, M. S. Johnson, N. Yoshida, and H. Svensmark Sulphuric acid is an important factor in aerosol nucleation and growth. It has been shown that ions enhance the formation of sulphuric acid aerosols, but the exact mechanism has remained undetermined. Furthermore some studies have found a deficiency in the sulphuric acid budget, suggesting a missing source. In this study the production of sulphuric acid from SO 2 through a number of different pathways is investigated. The production methods are standard gas phase oxidation by OH radicals produced by ozone photolysis with UV light, liquid phase oxidation by ozone, and gas phase oxidation initiated by gamma rays. The distributions of stable sulphur isotopes in the products and substrate were measured using isotope ratio mass spectrometry. All methods produced sulphate enriched in 34 S and we find a δ 34 S value of 8.7 ± 0.4‰ (1 standard deviation) for the UV-initiated OH reaction. Only UV light (Hg emission at 253.65 nm) produced a clear non-mass-dependent excess of 33 S. The pattern of isotopic enrichment produced by gamma rays is similar, but not equal, to that produced by aqueous oxidation of SO 2 by ozone. This, combined with the relative yields of the experiments, suggests a mechanism in which ionising radiation may lead to hydrated ion clusters that serve as nanoreactors for S(IV) to S(VI) conversion.

Description: First intercalibration of column-averaged methane from the Total Carbon Column Observing Network and the Network for the Detection of Atmospheric Composition Change Atmospheric Measurement Techniques Discussions, 5, 1355-1379, 2012 Author(s): F. Forster, R. Sussmann, M. Rettinger, N. M. Deutscher, D. W. T. Griffith, N. Jones, and P. K. Patra We present the intercalibration of dry-air column-averaged mole fractions of methane (XCH 4 ) retrieved from solar FTIR measurements of the Network for the Detection of Atmospheric Composition Change (NDACC) in the mid-infrared (MIR) versus near-infrared (NIR) soundings from the Total Carbon Column Observing Network (TCCON). The study uses multi-annual quasi-coincident MIR and NIR measurements from the stations Garmisch, Germany (47.48° N, 11.06° E, 743 m a.s.l.) and Wollongong, Australia (34.41° S, 150.88° E, 30 m a.s.l.). Direct comparison of the retrieved MIR and NIR time series shows a phase shift in XCH 4 seasonality, i.e. a significant time-dependent bias leading to a standard deviation (stdv) of the difference time series (NIR-MIR) of 8.4 ppb. After eliminating differences in a prioris by using ACTM-simulated profiles as a common prior, the seasonalities of the (corrected) MIR and NIR time series agree within the noise (stdv = 5.2 ppb for the difference time series). The difference time series (NIR-MIR) do not show a significant trend. Therefore it is possible to use a simple scaling factor for the intercalibration without a time-dependent linear or seasonal component. Using the Garmisch and Wollongong data together, we obtain an overall calibration factor MIR/NIR = 0.9926(18). The individual calibration factors per station are 0.9940(14) for Garmisch and 0.9893(40) for Wollongong. They agree within their error bars with the overall calibration factor which can therefore be used for both stations. Our results suggest that after applying the proposed intercalibration concept to all stations performing both NIR and MIR measurements, it should be possible to obtain one refined overall intercalibration factor for the two networks. This would allow to set up a harmonized NDACC and TCCON XCH 4 data set which can be exploited for joint trend studies, satellite validation, or the inverse modeling of sources and sinks.

Description: Revised identification of tropical oceanic cumulus congestus as viewed by CloudSat Atmospheric Chemistry and Physics, 12, 1587-1595, 2012 Author(s): S. P. F. Casey, E. J. Fetzer, and B. H. Kahn Congestus cloud convective features are examined in one year of tropical oceanic cloud observations from the CloudSat/CALIPSO instruments. Two types of convective clouds (cumulus and deep convective, based on classification profiles from radar), and associated differences in radar reflectivity and radar/lidar cloud-top height are considered. Congestus convective features are defined as contiguous convective clouds with heights between 3 and 9 km. Three criteria were used in previous studies to identify congestus: (1) CloudSat and CALIPSO cloud-top heights less than 1 km apart; (2) CloudSat 0 dBZ echo-top height less than 1 km from CloudSat cloud-top height, and (3) CloudSat 10 dBZ echo-top height less than 2 km from CloudSat cloud-top height. A majority of congestus convective features satisfy the second and third requirements. However, over 40% of convective features identified had no associated CALIPSO cloud-top height, predominantly due to the extinguishment of the lidar beam above the CloudSat-reported convective cloud. For the remaining cells, approximately 56% of these satisfy all three requirements; when considering the lidar beam-extinction issue, only 31% of congestus convective features are identified using these criteria. This implies that while previous methods used to identify congestus clouds may be accurate in finding vigorous convection (such as transient congestus rising toward the tropopause), these criteria may miss almost 70% of the total observed congestus convective features, suggesting a more general approach should be used to describe congestus and its surrounding environment.

Description: Wavelet-based spatial comparison technique for analysing and evaluating two-dimensional geophysical model fields Geoscientific Model Development, 5, 223-230, 2012 Author(s): S. Saux Picart, M. Butenschön, and J. D. Shutler Complex numerical models of the Earth's environment, based around 3-D or 4-D time and space domains are routinely used for applications including climate predictions, weather forecasts, fishery management and environmental impact assessments. Quantitatively assessing the ability of these models to accurately reproduce geographical patterns at a range of spatial and temporal scales has always been a difficult problem to address. However, this is crucial if we are to rely on these models for decision making. Satellite data are potentially the only observational dataset able to cover the large spatial domains analysed by many types of geophysical models. Consequently optical wavelength satellite data is beginning to be used to evaluate model hindcast fields of terrestrial and marine environments. However, these satellite data invariably contain regions of occluded or missing data due to clouds, further complicating or impacting on any comparisons with the model. This work builds on a published methodology, that evaluates precipitation forecast using radar observations based on predefined absolute thresholds. It allows model skill to be evaluated at a range of spatial scales and rain intensities. Here we extend the original method to allow its generic application to a range of continuous and discontinuous geophysical data fields, and therefore allowing its use with optical satellite data. This is achieved through two major improvements to the original method: (i) all thresholds are determined based on the statistical distribution of the input data, so no a priori knowledge about the model fields being analysed is required and (ii) occluded data can be analysed without impacting on the metric results. The method can be used to assess a model's ability to simulate geographical patterns over a range of spatial scales. We illustrate how the method provides a compact and concise way of visualising the degree of agreement between spatial features in two datasets. The application of the new method, its handling of bias and occlusion and the advantages of the novel method are demonstrated through the analysis of model fields from a marine ecosystem model.

Description: Moving beyond traditional model calibration or how to better identify realistic model parameters: sub-period calibration Hydrology and Earth System Sciences Discussions, 9, 1885-1918, 2012 Author(s): S. Gharari, M. Hrachowitz, F. Fenicia, and H. H. G. Savenije Conceptual hydrological models often rely on calibration for the identification of their parameters. As these models are typically designed to reflect real catchment processes, a key objective of an appropriate calibration strategy is the determination of parameter sets that reflect a "realistic" model behavior. Previous studies have shown that parameter estimates for different calibration periods can be significantly different. This questions model transposability in time, which is one of the key conditions for the set-up of a "realistic" model. This paper presents a new approach that selects parameter sets that provide a consistent model performance in time. The approach consists of confronting model performance in different periods, and selecting parameter sets that are as close as possible to the optimum of each individual sub-period. While aiding model calibration, the approach is also useful as a diagnostic tool, illustrating tradeoffs in the identification of time consistent parameter sets. The approach is demonstrated in a case study where we illustrate the multi-objective calibration of the HyMod hydrological model to a Luxembourgish catchment.

Description: Technical Note: Analytical sensitivity analysis of a two parameter recursive digital baseflow separation filter Hydrology and Earth System Sciences, 16, 451-455, 2012 Author(s): K. Eckhardt A sensitivity analysis for a well-established baseflow separation technique, a two parameter recursive digital filter, is presented. The sensitivity of the calculated baseflow index to errors or uncertainties of the two filter parameters and of the initial baseflow value is analytically ascertained. It is found that the influence of the initial baseflow value is negligible for long time series. The propagation of errors or uncertainties of the two filter parameters into the baseflow index is expressed by a dimensionless sensitivity index, the ratio between the relative error of the baseflow index and the relative error of the respective parameter. Representative index values are derived by application of the resulting equations to 65 North American catchments. In the mean the parameter a , the recession constant, has a stronger influence on the calculated baseflow index than the second filter parameter BFI max . This is favourable in that a can be determined by a recession analysis and therefore should be less uncertain. Whether this finding also applies for a specific catchment can easily be checked by means of the derived equations.

Description: The 2007 flood in the Sahel: causes, characteristics and its presentation in the media and FEWS NET Natural Hazards and Earth System Science, 12, 313-325, 2012 Author(s): C. Samimi, A. H. Fink, and H. Paeth During the rainy season in 2007, reports about exceptional rains and floodings in the Sahel were published in the media, especially in August and September. Institutions and organizations like the World Food Programme (WFP) and FEWS NET put the events on the agenda and released alerts and requested help. The partly controversial picture was that most of the Sahel faced a crisis caused by widespread floodings. Our study shows that the rainy season in 2007 was exceptional with regard to rainfall amount and return periods. In many areas the event had a return period between 1 and 50 yr with high spatial heterogeneity, with the exception of the Upper Volta basin, which yielded return periods of up to 1200 yr. Despite the strong rainfall, the interpretation of satellite images show that the floods were mainly confined to lakes and river beds. However, the study also proves the difficulties in assessing the meteorological processes and the demarcation of flooded areas in satellite images without ground truthing. These facts and the somewhat vague and controversial reports in the media and FEWS NET demonstrate that it is crucial to thoroughly analyze such events at a regional and local scale involving the local population.

Description: Factors selection in landslide susceptibility modelling on large scale following the gis matrix method: application to the river Beiro basin (Spain) Natural Hazards and Earth System Science, 12, 327-340, 2012 Author(s): D. Costanzo, E. Rotigliano, C. Irigaray, J. D. Jiménez-Perálvarez, and J. Chacón A procedure to select the controlling factors connected to the slope instability has been defined. It allowed us to assess the landslide susceptibility in the Rio Beiro basin (about 10 km 2 ) over the northeastern area of the city of Granada (Spain). Field and remote (Google EarthTM) recognition techniques allowed us to generate a landslide inventory consisting in 127 phenomena. To discriminate between stable and unstable conditions, a diagnostic area had been chosen as the one limited to the crown and the toe of the scarp of the landslide. 15 controlling or determining factors have been defined considering topographic, geologic, geomorphologic and pedologic available data. Univariate tests, using both association coefficients and validation results of single-variable susceptibility models, allowed us to select the best predictors, which were combined for the unique conditions analysis. For each of the five recognised landslide typologies, susceptibility maps for the best models were prepared. In order to verify both the goodness of fit and the prediction skill of the susceptibility models, two different validation procedures were applied and compared. Both procedures are based on a random partition of the landslide archive for producing a test and a training subset. The first method is based on the analysis of the shape of the success and prediction rate curves, which are quantitatively analysed exploiting two morphometric indexes. The second method is based on the analysis of the degree of fit, by considering the relative error between the intersected target landslides by each of the different susceptibility classes in which the study area was partitioned. Both the validation procedures confirmed a very good predictive performance of the susceptibility models and of the actual procedure followed to select the controlling factors.

Description: Spatial patterns of linear and nonparametric long-term trends in Baltic sea-level variability Nonlinear Processes in Geophysics, 19, 95-111, 2012 Author(s): R. V. Donner, R. Ehrcke, S. M. Barbosa, J. Wagner, J. F. Donges, and J. Kurths The study of long-term trends in tide gauge data is important for understanding the present and future risk of changes in sea-level variability for coastal zones, particularly with respect to the ongoing debate on climate change impacts. Traditionally, most corresponding analyses have exclusively focused on trends in mean sea-level. However, such studies are not able to provide sufficient information about changes in the full probability distribution (especially in the more extreme quantiles). As an alternative, in this paper we apply quantile regression (QR) for studying changes in arbitrary quantiles of sea-level variability. For this purpose, we chose two different QR approaches and discuss the advantages and disadvantages of different settings. In particular, traditional linear QR poses very restrictive assumptions that are often not met in reality. For monthly data from 47 tide gauges from along the Baltic Sea coast, the spatial patterns of quantile trends obtained in linear and nonparametric (spline-based) frameworks display marked differences, which need to be understood in order to fully assess the impact of future changes in sea-level variability on coastal areas. In general, QR demonstrates that the general variability of Baltic sea-level has increased over the last decades. Linear quantile trends estimated for sliding windows in time reveal a wide-spread acceleration of trends in the median, but only localised changes in the rates of changes in the lower and upper quantiles.

Description: Impact of spatial resolution on the modelling of the Greenland ice sheet surface mass balance between 1990–2010, using the regional climate model MAR The Cryosphere Discussions, 6, 635-672, 2012 Author(s): B. Franco, X. Fettweis, C. Lang, and M. Erpicum With the aim to force an ice dynamical model, the Greenland ice sheet (GrIS) surface mass balance (SMB) was modelled at different spatial resolutions (15–50 km) for the period 1990–2010, using the regional climate model MAR (Modèle Atmosphérique Régional) forced by the ERA-INTERIM reanalysis. This comparison revealed that (i) the inter-annual variability of the SMB components is consistent within the different spatial resolutions investigated, (ii) the MAR model simulates heavier precipitation on average over the GrIS with diminishing spatial resolution, and (iii) the SMB components (except precipitation) can be derived from a simulation at lower resolution with an ''intelligent'' interpolation. This interpolation can also be used to approximate the SMB components over another topography/ice sheet mask of the GrIS. These results are important for the forcing of an ice dynamical model, needed to enable future projections of the GrIS contribution to sea level rise over the coming centuries.