ALBERT

Description: ABSTRACT Particle number size distributions and hygroscopic properties of marine and Saharan dust aerosol were investigated during the SAMUM-2 field study at Cape Verde in winter 2008. Aitken and accumulation mode particles were mainly assigned to the marine aerosol, while coarse mode particles were composed of sea–salt and a variable fraction of Saharan mineral dust. A new methodical approach was used to derive hygroscopic growth and state of mixing for a particle size range (volume equivalent) from dp ve = 26 nm – 10 μm. For hygroscopic particles with dp ve 〈 100 nm, the median hygroscopicity parameter κ is 0.35. From 100 nm 〈 dp ve 〈 350 nm, κ increases to 0.65. For larger particles, κ at dp ve = 350 nm was used. For nearly hydrophobic particles, κ is between 0 and 0.1 for dp ve 〈 250 nm and decreases to 0 for dp ve 〉 250 nm. The mixing state of Saharan dust in terms of the number fraction of nearly hydrophobic particles showed the highest variation and ranges from 0.3 to almost 1. This study was used to perform a successful mass closure at ambient conditions and demonstrates the important role of hygroscopic growth of large sea-salt particles.

Description: ABSTRACT Two-point radon gradients provide a direct, unambiguous measure of near-surface atmospheric mixing. A 31-month dataset of hourly radon measurements at 2 and 50 m is used to characterise the seasonality and diurnal variability of radon concentrations and gradients at a site near Sydney. Vertical differencing allows separation of remote (fetch-related) effects on measured radon concentrations from those due to diurnal variations in the strength and extent of vertical mixing. Diurnal composites, grouped according to the maximum nocturnal radon gradient (ΔC max ), reveal strong connections between radon, wind, temperature and mixing depth on sub-diurnal timescales. Comparison of the bulk Richardson Number (Ri B ) and the turbulence kinetic energy (TKE) with the radon-derived bulk diffusivity (K B ) helps to elucidate the relationship between thermal stability, turbulence intensity and the resultant mixing. On nights with large ΔC max , K B and TKE levels are low and Ri B is well above the “critical” value. Conversely, when ΔC max is small, K B and TKE levels are high and Ri B is near zero. For intermediate ΔC max , however, Ri B remains small whereas TKE and K B both indicate significantly reduced mixing. The relationship between stability and turbulence is therefore non-linear, with even mildly stable conditions being sufficient to suppress mixing.

Description: ABSTRACT We apply methods from extreme value theory to identify extreme events in high (termed EHOs) and low (termed ELOs) total ozone and to describe the distribution tails (i.e., very high and very low values) of five long-term European ground-based total ozone time series. The influence of these extreme events on observed mean values, long-term trends and changes is analyzed. The results show a decrease in EHOs and an increase in ELOs during the last decades, and establish that the observed downward trend in column ozone during the 1970s-1990s is strongly dominated by changes in the frequency of extreme events. Further it is shown that clear “fingerprints” of atmospheric dynamics (NAO, ENSO) and chemistry (ozone depleting substances (ODS), polar vortex ozone loss) can be found in the frequency distribution of ozone extremes, even if no attribution is possible from standard metrics (e.g., annual mean values). The analysis complements earlier analysis for the world's longest total ozone record at Arosa, Switzerland, confirming and revealing the strong influence of atmospheric dynamics on observed ozone changes. The results provide clear evidence that in addition to ODS, volcanic eruptions and strong/moderate ENSO and NAO events had significant influence on column ozone in the European sector.

Description: ABSTRACT A new sectional aerosol dynamics model, MAFOR, was developed with the focus to study nucleation in the marine boundary layer. Novel aspects of the model are 1) flexibility in the treatment of gas phase chemistry, 2) treatment of liquid phase chemistry, which can be extended according to needs, and 3) simultaneous calculation of number and mass concentration distributions of a multicomponent aerosol as functions of time. Comparison with well-documented aerosol models (MONO32 and AEROFOR), a comprehensive dataset on gas phase compounds, aerosol size distribution and chemical composition obtained during the AOE-96 (Arctic Ocean Expedition, 1996) was used to evaluate the model. Dimethyl sulphide decay during advection of an air parcel over the Arctic pack ice was well captured by the applied models and predicted concentrations of gaseous sulphuric acid and methane sulphonic acid range up to 1.0 × 10 6 cm −3 and 1.8 × 10 6 cm −3 , respectively. Different nucleation schemes were implemented in MAFOR which allow the simulation of new particle formation. Modelled nucleation rates from sulphuric acid nucleation via cluster activation were up to 0.21 cm −3 s −1 while those from ion-mediated nucleation were below 10 −2 cm −3 s −1 . Classical homogeneous binary and ternary nucleation theories failed to predict nucleation over the central Arctic Ocean in summer.

Description: ABSTRACT Ground based high spectral resolution measurements of downwelling radiances from 800 to 1200 cm −1 were conducted between 20 January and 6 February 2008 within the scope of the SAMUM-2 field experiment. We infer the spectral signature of mixed biomass burning/mineral dust aerosols at the surface from these measurements and at top of the atmosphere from IASI observations. In a case study for a day characterised by the presence of high loads of both dust and biomass we attempt a closure with radiative transfer simulations assuming spherical particles. A detailed sensitivity analysis is performed to investigate the effect of uncertainties in the measurements ingested into the simulation on the simulated radiances. Distinct deviations between modelled and observed radiances are limited to a spectral region characterised by resonance bands in the refractive index. A comparison with results obtained during recent laboratory studies and field experiments reveals, that the deviations could be caused by the aerosol particles’ non-sphericity, although an unequivocal discrimination from measurement uncertainties is not possible. Based on radiative transfer simulations we estimate the aerosol's direct radiative effect in the atmospheric window region to be 8 Wm −2 at the surface and 1 Wm −2 at top of the atmosphere.

Description: ABSTRACT An observation-based numerical study of humidity-dependent aerosol optical properties of mixed marine and Saharan mineral dust aerosol is presented. An aerosol model was developed based on measured optical and microphysical properties to describe the marine and Saharan dust aerosol at Cape Verde. A wavelength-dependent optical equivalent imaginary part of the refractive index and a scattering non-sphericity factor for Saharan dust were derived. Simulations of humidity effects on optical properties by the aerosol model were validated with relative measurements of the extinction coefficient at ambient conditions. Parameterizations were derived to describe the humidity dependence of the extinction, scattering, and absorption coefficients as well as the asymmetry parameter and single scattering albedo. For wavelengths (300 – 950 nm) and dry dust volume fractions (0 – 1), aerosol optical properties as a function of relative humidity (0 – 90%) can be calculated from tabulated parameters. For instance, at a wavelength of 550 nm, a volume fraction of 0.5 of dust on the total particle volume (dry conditions) and a relative humidity of 90%, the enhancements for the scattering, extinction, and absorption coefficients are 2.55, 2.46, and 1.04, respectively, while the enhancements for the asymmetry parameter and single scattering albedo are 1.11 and 1.04.

Description: ABSTRACT Airborne measurements of upward solar spectral irradiances were performed during the second Saharan Mineral dUst experiMent (SAMUM–2) campaign based on the Cape Verde Islands. Additionally, airborne high resolution lidar measurements of vertical profiles of particle extinction coefficients were collected in parallel to the radiation data. Aerosol layers of Saharan dust, partly mixed with biomass burning smoke, were probed. With corresponding radiative transfer simulations the single scattering albedo and the asymmetry parameter of the aerosol particles were derived although with high uncertainty. The broadband aerosol solar radiative forcing at the top of atmosphere was calculated and examined as a function of the aerosol types. However, but due to uncertainties in both the measurements and the calculations the chemical composition cannot be identified. In addition, a mostly measurement-based method to derive the broadband aerosol solar radiative forcing was used. This approach revealed clear differences of broadband net irradiances as a function of the aerosol optical depth. The data were used to identify different aerosol types from different origins. Higher portions of biomass burning smoke lead to larger broadband net irradiances.

Description: ABSTRACT PM 2.5 and PM 10 samples collected at a suburban site of northeastern part of India have been analyzed for particle mass, total carbon (TC), water soluble total carbon (WSTC), water soluble organic carbon (WSOC), water soluble inorganic carbon (WSIC), organic acids (formic, acetic, proponoic and oxalic acids) along with inorganic ions (NO 3 − , SO 4 2− , NH 4 − ). Most of the PM 10 consist of PM 2.5 in the present site (ratio 54–74%). WSTC content in PM 2.5 and PM 10 corresponds to 21% and 16%, respectively of their total particle masses. Thermo gravimetric analysis showed the presence of humic like substances (16–22%) in particulate samples. Domestic heating and stagnant atmospheric conditions enhanced the levels of these carbonaceous compounds in PM 2.5 and PM 10 in winter. Qualitative estimation of various functional groups by Fourier Transform Infra Red (FTIR) analysis indicates the presence of carboxylic, hydroxyl, aliphatic and aromatic hydrocarbons, amines and sulphurous compounds in these aerosols. Absolute principal component analysis applied on the aerosol data resolves four factors. These factors are associated with carbonaceous aerosols released from combustion of coal and wood, secondary inorganic and organic aerosols, and water soluble inorganic fraction.

Description: ABSTRACT The spatio-temporal evolution of the Saharan dust and biomass burning plume during the SAMUM-2 field campaign in January and February 2008 is simulated at 28∼km horizontal resolution with the regional model-system COSMO-MUSCAT. The model performance is thoroughly tested using routine ground-based and space-borne remote sensing and local field measurements. Good agreement with the observations is found in many cases regarding transport patterns, aerosol optical thicknesses and the ratio of dust to smoke aerosol. The model also captures major features of the complex aerosol layering. Nevertheless, discrepancies in the modelled aerosol distribution occur, which are analysed in detail. The dry synoptic dynamics controlling dust uplift and transport during the dry season are well described by the model, but surface wind peaks associated with the breakdown of nocturnal low-level jets are not always reproduced. Thus, a strong dust outbreak is underestimated. While dust emission modelling is a priori more challenging, since strength and placement of dust sources depend on on-line computed winds, considerable inaccuracies also arise in observation-based estimates of biomass burning emissions. They are caused by cloud and spatial errors of satellite fire products and uncertainties in fire emission parameters, and can lead to unrealistic model results of smoke transport.

Description: ABSTRACT During the SAMUM-2 experiment, spectral absorption coefficients, single scattering albedos, and imaginary parts of refractive indices of mineral dust particles were investigated at the Cape Verde Islands. Main absorbing constituents of airborne samples were mineral dust and soot. PM 10 spectral absorption coefficients were measured using a Spectral Optical Absorption Photometer (SOAP) covering the wavelength range from 300 to 960 nm with a resolution of 25 nm. From SOAP, also information on the particle scattering coefficients could be retrieved. Spectral single scattering albedos were obtained in the wavelength range from 350 to 960 nm. Imaginary parts of the refractive index were inferred from measured particle number size distributions and absorption coefficients using Mie scattering theory. Imaginary parts for a dust case were 0.012, 0.0047, and 0.0019 at the wavelengths 450, 550, and 950 nm, respectively, and the single scattering albedos were 0.91, 0.96, and 0.98 at the same wavelengths. During a marine case, the imaginary parts of the refractive indices were 0.0045, 0.0040, and 0.0036 and single scattering albedos were 0.93, 0.95, and 0.96 at the wavelengths given above.

Description: ABSTRACT In the framework of the Saharan Mineral Dust Experiment (SAMUM) airborne High Spectral Resolution Lidar and in situ measurements of the particle size, aerosol mixing state and absorption coefficient were conducted. Here, the properties of mineral dust and tropical biomass burning layers in the Cape Verde region in January/February 2008 are investigated and compared with the properties of fresh dust observed in May/June 2006 close the Sahara. In the Cape Verde area, we found a complex stratification with dust layers covering the altitude range below 2 km, and biomass burning layers aloft. The aerosol type of the individual layers was classified based on depolarization and lidar ratios and, in addition, on in situ measured Ångström exponents of absorption å ap . The dust layers had a depth of 1.3±0.4 km, and showed a median å ap of 3.95. The median effective diameter D eff was 2.5 μm, and the dust layers over Cape Verde yielded clear signals of aging: large particles were depleted due to gravitational settling, and the accumulation mode diameter was shifted towards larger sizes as a result of coagulation. The tropical biomass layers had a depth of 2.0±1.1 km and were characterized by a median å ap of 1.34. They always contained a certain amount of large dust particles and showed a median D eff of 1.1 μm and a fine mode D eff, fine of 0.33. The dust and biomass burning layers had a median aerosol optical depth (AOD) of 0.23 and 0.09, respectively. The median contributions to the AOD of the total atmospheric column below 10 km were 75% and 37%, respectively.

Description: ABSTRACT The work focuses on the analysis of CO 2 and O 3 surface variations observed during five summer experimental campaigns carried out at the “Icaro Camp” clean air facility (74.7° S, 164.1° E, 41 m a.s.l) of the “Mario Zucchelli” Italian coastal research station. This experimental activity allowed the definition of summer average background O 3 values that ranged from 18.3 ± 4.7 ppbv (summer 2005 – 2006) to 21.3 ± 4.0 ppbv (summer 2003 – 2004). Background CO 2 concentrations showed an average growth rate of 2.10 ppmv/yr, with the highest CO 2 increase between the summer campaigns 2002-2003 and 2001-2002 (+2.85 ppmv/yr), probably reflecting the influence of the 2002/2003 ENSO event. A comparison with other Antarctic coastal sites suggested that the summer background CO 2 and O 3 at MZS-IC are well representative of the average conditions of the Ross Sea coastal regions. As shown by the analysis of local wind direction and by 3D back-trajectory calculations, the highest CO 2 and O 3 values were recorded in correspondence to air masses flowing from the interior of the Antarctic continent. These results suggest that air mass transport from the interior of the continent exert an important influence on air mass composition in Antarctic coastal areas.

Description: ABSTRACT Simultaneous measurements of aerosol black carbon (BC) in both fresh snow and in air on Svalbard are presented. From these, washout ratios for BC are calculated and compared to sparse previous measurements of this metric in the arctic. The current ratios are significantly higher than previously found measured values. We argue that the degree of snow riming within the accretion zone can explain most of this difference. Using an analytical model of the scavenging process, BC scavenging efficiencies are estimated to lie in the range 0.25–0.5, comparable to measured values.

Description: ABSTRACT Satellite ocean tracer images, of Sea Surface Temperature (SST) and Ocean Colour images, for example, show patterns like fronts and filaments that characterise the flow dynamics. These patterns can be described using Lagrangian tools such as Finite-Time Lyapunov Exponents (FTLE) or Finite-Time Lyapunov Vectors (FTLV). In recent years, several studies have investigated the possibility of directly assimilating structured data from satellite images into numerical models. In this paper, we exploit specific properties of FTLE and FTLV to define observation operators that can be used in a direct ocean tracer image assimilation scheme. In an idealised context, we show that high-resolution SST and Ocean Colour images can be exploited to correct velocity fields using FTLE or FTLV.

Description: ABSTRACT Although salt rejection from sea ice is a key process in deep-water formation in ice-covered seas, the concurrent rejection of CO 2 and the subsequent effect on air-sea CO 2 exchange have received little attention. We review the mechanisms by which sea ice directly and indirectly controls the air-sea CO 2 exchange and use recent measurements of inorganic carbon compounds in bulk sea ice to estimate that oceanic CO 2 uptake during the seasonal cycle of sea-ice growth and decay in ice-covered oceanic regions equals almost half of the net atmospheric CO 2 uptake in ice-free polar seas. This sea-ice-driven CO 2 uptake has not been considered so far in estimates of global oceanic CO 2 uptake. Net CO 2 uptake in sea-ice-covered oceans can be driven by; i ) rejection during sea-ice formation and sinking of CO 2 -rich brine into intermediate and abyssal oceanic water masses, ii ) blocking of air-sea CO 2 exchange during winter, and iii ) release of CO 2 -depleted melt water with excess total alkalinity during sea-ice decay, and iv ) biological CO 2 drawdown during primary production in sea ice and surface oceanic waters.

Description: ABSTRACT A two-dimensional fine-scale atmospheric model was set across an idealized 80 km wide east-west sea gulf at 60 o N (‘Gulf of Finland’). During a moderate south-easterly basic flow in overcast early summer conditions a robust low-level jet (LLJ) is formed, with diverging and relatively strong afternoon surface easterlies blowing along the cool gulf. The LLJ is caused primarily by inertial oscillation in space-time due to the large difference in roughness and stability over the land and the sea, but the surface easterlies are also enhanced by an anti-heat island circulation triggered by the slant basic flow across the cool sea gulf. The dynamics and details of the anti-heat island circulation are discussed. With warmer waters the primary LLJ relaxes and the anti-heat island circulation ceases while the enhanced vertical mixing still maintains strong surface winds over the warm sea, but with reduced cross-isobar angles. Sunny conditions enhance convection over land and may induce sea breezes. These may reinforce the LLJ and the associated surface easterlies over the sea.

Description: ABSTRACT The SAMUM-2 experiment took place in the Cape Verde islands in January-February 2008. The co-located ground-based and airborne instruments allow the study of desert dust optical and microphysical properties in a closure experiment. The Meteorological Institute of the University of Munich deployed one sun-sky photometer and 2 tropospheric lidar systems. A traveling AERONET-Cimel sun-sky radiometer was also deployed. During the measurement period the aerosol scenario over Cape Verde mostly consisted of a dust layer below 2 km and a smoke-dust layer above 2–4 km a.s.l. The Saharan dust arrived at the site from the NE, whereas the smoke originated in the African equatorial region. This paper describes the main results of the Sun photometer observations, supported by lidar information. An analysis of the variations in the aerosol optical depth in the range 340–1550 nm, the Ångström exponent, volume size distributions and single scattering albedo is presented. The aerosol mixtures are analyzed by means of the fine mode fraction of the aerosol optical depth provided by the sun-sky inversion data and the Spectral Deconvolution Algorithm. The mean AOD (500 nm) was 0.31, with associated low Ångström exponent of 0.46. Several types of events were detected within the dataset, with prevalence of dust or mixtures as characterized by the Ångström exponents of extinction and absorption and the fine mode fraction. Aerosol properties derived from sunphotometry were compared to in situ measurements of size distribution, effective radius and single scattering albedo.

Description: ABSTRACT The snow surface on thick multiyear sea ice in winter is on average colder than the air because of the negative radiation balance. Beneath the snow surface there is a strong temperature gradient in winter with increasing temperatures towards the ice-water interface temperature at the freezing point around -1.8 °C. The sea ice surface temperature and the thermal microwave brightness temperature were simulated using a combination of thermodynamic and microwave emission models. The simulations indicate that the physical snow-ice interface temperature or alternatively the 6 GHz effective temperature have a good correlation with the effective temperature at the temperature sounding channels near 50 GHz. The complete correlation matrix based on the simulations for physical and effective temperatures is given. The physical snow-ice interface temperature is related to the brightness temperature at 6 GHz vertical polarisation as expected. However, the emissivity factor normally used when converting brightness temperature to the ice temperature is dependent on the ice temperature. The simulations indicate that a simple model may be used to derive the snow-ice interface temperature from satellite AMSR 6 GHz measurements.

Description: ABSTRACT The provenance of fine-grained eolian dust over East Asia is distinguished using a regional climate model. Five major source regions within China and Mongolia are considered: sandy lands in the northeastern China, deserts in the northern China, the Gobi deserts, the Taklimakan deserts in western China and deserts on the Tibet Plateau. The contribution of each dust source is evaluated for the downwind eolian sediments in the Chinese Loess Plateau (CLP) and Japan Sea (JS). The results show that the adjoining northern and Gobi deserts dominate the dust depositions over CLP and over eastern China, although Taklimakan deserts are actually the largest emission source. On the marine deposits in JS, Taklimakan deserts exert a more significant role since the particles from Taklimakan tend to be raised into upper atmosphere and delivered for a longer distance. The agent for dust delivery also differs among different sources. Dust from northern deserts is dominantly carried by the local northwesterly winds in spring associated with the East Asian winter monsoon system and restricted in the low-level atmosphere, while the westerly winds in the mid- to high-level troposphere become of great importance and more likely to be responsible for the transport of Taklimakan dust.

Description: ABSTRACT Radiative fields of three-dimensional inhomogeneous Saharan dust clouds have been calculated at solar wavelength (0.6 μm) by means of a Monte Carlo radiative transfer model. Scattering properties are taken from measurements in the SAMUM campaigns, from light scattering calculations for spheroids based on the MIESCHKA code, from Mie theory for spheres and from the geometric optics method assuming irregular shaped particles. Optical properties of different projected area equivalent shapes are compared. Large differences in optical properties are found especially in the phase functions. Results of radiative transfer calculations based on the Monte Carlo method are shown exemplarily for one dust cloud simulated by the cloud resolving atmospheric circulation model LM-MUSCAT-DES. Shape induced differences in the radiation fluxes are pronounced, for example, the domain averaged normalized radiance is about 30% lower in the case of a dust plume consisting of spheroids or irregular particles compared to spheres. The effect of net horizontal photon transport (3D-effect) on the reflected radiance fields is only notable at the largest gradients in optical thickness. For example, the reflectance at low sun position differs locally about 15% when horizontal photon transport is accounted for. ‘Sharp edges’ due to 1D calculations are smoothed out in the 3D case.

Description: ABSTRACT We model lidar-relevant optical properties of mineral dust aerosols and compare the modeling results with optical properties derived from lidar measurements during the SAMUM field campaigns. The Discrete Dipole Approximation is used for optical modeling of single particles. For modeling of ensemble properties, the OPAC desert aerosol type is extended by mixtures of absorbing and non-absorbing irregularly-shaped mineral dust particles. Absorbing and non-absorbing particles are mixed in the model ensembles to mimic the natural mineralogical inhomogeneity of dust aerosols. A sensitivity study reveals that the mineralogical inhomogeneity is critical for the lidar ratio at short wavelengths; it has to be considered in models for agreement with the observed wavelength dependence of the lidar ratio. The amount of particles with low aspect ratios (about 1.4 and lower) affects the lidar ratio at any lidar wavelength; their amount has to be low for agreement with SAMUM observations. Irregularly-shaped dust particles with typical refractive indices, in general, have higher linear depolarization ratios than corresponding spheroids, and improve the agreement with observations.

Description: ABSTRACT The direct radiative forcing and dynamic atmospheric response due to Saharan dust and biomass burning aerosol particles are presented for a case study during the SAMUM-2 field campaign in January and February 2008. The regional model system COSMO-MUSCAT is used. It allows online interaction of the computed dust and smoke load with the solar and terrestrial radiation and with the model dynamics. Model results of upward solar irradiances are evaluated against airborne radiation measurements in the Cape Verde region. The comparison shows a good agreement for the case of dust and smoke mixture. Dust and smoke particles influence the atmospheric dynamics by changing the radiative heating rates. The related pressure perturbations modify local and synoptic scale air-flow patterns. In the radiative feedback simulations, the Hadley circulation is enhanced and convergence zones occur along the Guinea coast. Thus, the smoke particles spread more than 5° further north and the equatorward transport is reduced. Within the convergence zones Saharan dust and biomass burning material are more effectively advected towards the Cape Verdes. Given the model uncertainties, the agreement between the modelled and observed aerosol distribution is locally improved when aerosol-radiation interaction is considered.

Description: ABSTRACT The impact of parameter variations on the Navy Operational Global Atmospheric Prediction System ensemble performance is examined, and subsets of ensemble members are used to identify the relative impact of the individual parameters. Two sets of parameter variations are considered. The first set has variations in the parameterization of cumulus convection only. The second set has variations in both convection and boundary layer parameterizations. In the tropics, parameter variations significantly increase ensemble spread in wind and temperature fields, and significantly reduce Brier scores for low-level wind speed and temperature, primarily through improvements to the reliability (the impact in the extratropics is negligible). There are also small but significant improvements in the ensemble mean tropical cyclone track forecasts. For the metrics considered here, the second set of parameter variations outperforms the first set. Examination of the spread within ensemble subsets suggests that the parameter with the biggest impact is the one that controls the maximum negative temperature perturbation a lifted parcel is allowed to have below its level of free convection. Variations in the von Kármán constant significantly increase ensemble spread in the low-level tropical winds near the date line, and in the low-level temperature field throughout the tropics and subtropics.

Description: ABSTRACT This study extrapolates aerosol data of the CARIBIC project from 1997 until June 2008 in along trajectories to compose large scale maps and vertical profiles of sub-micrometer particle concentrations in the UT/LMS. The extrapolation was validated by comparing extrapolated values with CARIBIC data measured near the respective trajectory position and by comparing extrapolated CARIBIC data to measurements by other experiments near the respective trajectory positions. Best agreement between extrapolated and measured data is achieved with particle lifetimes longer than the maximum length of utilized trajectories. The derived maps reveal regions of strong and frequent new particle formation, namely the Tropical Central and Western Africa with the adjacent Atlantic, South America, the Caribbean, and South-East Asia. These regions of particle formation coincide with those of frequent deep convective clouds. Vertical particle concentration profiles for the troposphere and the stratosphere confirm statistically previous results indicating frequent new particle formation in the tropopause region. There was no statistically significant increase in Aitken mode particle concentration between the first period of CARIBIC operation, 1997-• 2002, and the second period, 2004-• 2009. However, a significant increase in concentration occurred within the latter period when considering it in isolation.

Description: ABSTRACT We investigated the variability of 210 Pb, 7 Be and 10 Be in coastal Antarctic aerosol samples based on continuous, monthly and annually resolved time series obtained from Neumayer Station over the period 1983 to 2008. Clear seasonal cycles peaking in the local summer half year stand out as a common feature of all three radionuclide records. Time series analyses suggest that significant multi-annual changes are confined to a 4–6 years periodicity resembling that of the Southern Annual Mode index in case of 210 Pb and to the expected decadal solar cycle in case of the cosmogenic Be-isotopes. Both, changes in the meridional transport and surface inversion strength appear to drive the seasonal 210 Pb cycle, which generally peaks in November. In contrast, stratospheric air mass intrusions are proved to be the main reason for the Be-isotopes seasonality. This finding is revealed by enhanced 10 Be/ 7 Be ratios occurring during late summer / early autumn broadly concurrently with the individual Be-isotopes and the 7 Be/ 210 Pb ratio. The 10 Be and 7 Be records clearly reflect the decadal, solar-modulated production signal but, for unknown reasons, they substantially differ in their detailed pattern. It is ruled out, that an excess 7 Be production by solar energetic particles was responsible for this mismatch.

Description: ABSTRACT The previous singular-value formulations for measuring information content from observations are transformed into spectral forms in the wavenumber space for univariate analyses of uniformly distributed observations. The transformed spectral formulations exhibit the following advantages over their counterpart singular-value formulations: (i) The information contents from densely distributed observations can be calculated very efficiently even if the background and observation space dimensions become both too large to compute by using the singular-value formulations. (ii) The information contents and their asymptotic properties can be analyzed explicitly for each wavenumber. (iii) Super-observations can be not only constructed by a truncated spectral expansion of the original observations with zero or minimum loss of information but also explicitly related to the original observations in the physical space. The spectral formulations reveal that (i) uniformly thinning densely distributed observations will always cause a loss of information and (ii) compressing densely distributed observations into properly coarsened super-observations by local averaging may cause no loss of information under certain circumstances.

Description: ABSTRACT In order to assess the potential of regional climate models to be used to project future weather events, a first step is to study the regional model forced by actual weather, or more precisely by reanalysis of weather data. In this paper we investigate how well the Norwegian regional model HIRHAM, forced by ERA-40 reanalysis data, compares to observed precipitation data from the Norwegian Meteorological Institute over Norwegian mainland. This paper aims to show how standard methods of statistical testing may be used to assess dynamic downscaling. Methods considered are the Kolmogorov-Smirnov two-sample test, a Fisher exact test for equality of quantiles, an Extreme Value Theory test, where equality of the one-year return levels are tested, and equality of wet day frequency. All tests are performed seasonally. The regional model is skillful in describing the lower quartile of the precipitation distribution, but underestimates higher levels of precipitation. Our results indicate that the regional model has too many but too small rain events for all seasons.

Description: ABSTRACT A wind Doppler lidar was deployed next to three aerosol lidars during the SAMUM–2 campaign on the main island of Cape Verde. The effects of the differential heating of the island and the surrounding ocean and the orographic impact of the capital island Santiago and the small island on its luv side, Maio, are investigated. Horizontal and vertical winds were measured in the disturbed maritime boundary layer and compared to local radiosoundings. Lidar measurements from the research aircraft Falcon and a 3-D Large Eddy Simulation (LES) model were used in addition to study the heating effects on the scale of the islands. Indications are found that these effects can widely control the downward mixing from greater heights to the surface of African aerosols, mainly Saharan dust and biomass-burning smoke, which were detected in a complex layering over the Cape Verde region.

Description: ABSTRACT A large field experiment of the Saharan Mineral Dust Experiment (SAMUM) was performed in Praia, Cape Verde, in January and February 2008. This work reports on the aerosol mass concentrations, size distributions, and mineralogical composition of the aerosol arriving at Praia. Three dust periods were recorded during the measurements, divided by transitional periods and embedded in maritime-influenced situations. The total suspended particle mass/PM 10 /PM 2.5 were 250/180/74μg/m 3 on average for the first dust period (17 to 21 January) and 250/230/83μg/m 3 for the second (24 to 26 January). The third period (28 January to 2 February) was the most intensive with 410/340/130μg/m 3 . Four modes were identified in the size distribution. The first mode (50–70nm) and partly the second (700–1100nm) can be regarded as of marine origin, but some dust contributes to the latter. The third mode (2–4μm) is dominated by advected dust, while the intermittently occurring fourth mode (15–70μm) may have a local contribution. The dust consisted of kaolinite (dust/maritime period: 35%wt./25%wt.), K-feldspar (20%wt./25%wt.), illite (14%wt./10%wt.), quartz (11%wt./8%wt.), smectites (6%wt./4%wt.), plagioclase (6%wt./1%wt.), gypsum (4%wt./7%wt.), halite (2%wt./17%wt.), and calcite (2%wt./3%wt.).

Description: ABSTRACT Lidar measurements of mixed dust/smoke plumes over the tropical Atlantic ocean were carried out during the winter campaign of SAMUM-2 at Cape Verde. Profiles of backscatter and extinction coefficients, lidar ratios, and Ångström exponents related to pure biomass–burning aerosol from southern West Africa were extracted from these observations. Furthermore, these findings were used as input for an inversion algorithm to retrieve microphysical properties of pure smoke. Seven measurement days were found suitable for the procedure of aerosol–type separation and successive inversion of optical data that describe biomass–burning smoke. We inferred high smoke lidar ratios of 87 ± 17 sr at 355 nm and 79 ± 17 sr at 532 nm. Smoke lidar ratios and Ångström exponents are higher compared to the ones for the dust/smoke mixture. These numbers indicate higher absorption and smaller sizes for pure smoke particles compared to the dust/smoke mixture. Inversion of the smoke data set results in mean effective radii of 0.22 ± 0.08 μm with individual results varying between 0.10 and 0.36 μm. The single–scattering albedo for pure biomass–burning smoke was found to vary between 0.63 and 0.89 with a very low mean value of 0.75 ± 0.07. This is in good agreement with findings of airborne in–situ measurements which showed values of 0.77 ± 0.03. Effective radii from the inversion were similar to the ones found for the fine mode of the in-situ size distributions. It is assumed that this is caused by impossibility of an accurate separation of the influences of mineral dust and biomass–burning smoke to the measured optical properties.

Description: ABSTRACT This paper examines available data, develops a strategy, and presents a monthly, global time series of fossil-fuel carbon dioxide emissions for the years 1950 to 2006. This monthly time series was constructed from detailed study of monthly data from the 21 countries that account for approximately 80% of global total emissions. These data were then used in a Monte Carlo approach to proxy for all remaining countries. The proportional-proxy methodology estimates by fuel group the fraction of annual emissions emitted in each country and month. Emissions from solid, liquid, and gas fuels are explicitly modeled by the proportional-proxy method. The primary conclusion from this study is the global monthly time series is statistically significantly different from a uniform distribution throughout the year. Uncertainty analysis of the data presented show that the proportional-proxy method used faithfully reproduces monthly patterns in the data and the global monthly pattern of emissions is relatively insensitive to the exact proxy assignments used. The data and results presented here should lead to a better understanding of global and regional carbon cycles, especially when the mass data are combined with the stable carbon isotope data in atmospheric transport models.

Description: ABSTRACT The isotopic composition of precipitation has been measured in samples simultaneously collected during individual precipitation events at two neighboring high-altitude stations (Houxia at 2100 m.a.s.l. and Gaoshan at 3545 m.a.s.l.) in the Tianshan Mts., northwest China. The observed changes of δ 18 O (δ 2 H) and deuterium excess with surface air temperature, altitude and season have been evaluated to derive information on the effects of sub-cloud evaporation and moisture recycling on the formation of precipitation and its isotopic composition under arid climatic conditions. Consulting the long-term monthly averages of d excess and temperature of the nearest GNIP station Wulumuqi, a striking similarity was found with the results of the two high-altitude stations concerning the relation between d excess and temperature. The d excess – temperature plot of the Wulumuqi data shows an hysteresis effect which appears to signify seasonal changes in the interplay between sub-cloud evaporation and moisture recycling. Finally, for the first time a negative altitude gradient of the d excess has been found for all stations including two more GNIP stations in northwest China but far away from the study area. This “inverse altitude effect” may manifest a decrease of the recycled fraction in air moisture with altitude.

Description: ABSTRACT A new and consistent convection scheme, providing continuous treatment of this atmospheric process, is described. The main concept ensuring the consistency of the whole system is buoyancy, a key element of any convective vertical motion. The buoyancy constitutes the forcing term of the convective vertical velocity, which is then used to define the triggering condition, the mass flux, and the rates of entrainment-detrainment. The buoyancy is also used in its vertically integrated form to express the closure condition as a CAPE relaxation. The continuous treatment of convection from dry thermals to deep precipitating cumulus is made possible through the use of a continuous formulation of the entrainment-detrainment rates and CAPE relaxation time, together with an embedded precipitation scheme. This convection scheme is first evaluated with the help of single-column model simulations of specific case-studies encompassing a variety of convective situations. Second, a coupled general-circulation model multi-year simulation is provided as a means to assess the model climate with respect to observations.

Description: ABSTRACT When constraining surface emissions of air pollutants using inverse modeling one often encounters spurious corrections to the inventory at places where emissions and observations are co-located, referred to here as the co-localization problem. Several approaches have been used to deal with this problem: coarsening the spatial resolution of emissions; adding spatial correlations to the covariance matrices; adding constraints on the spatial derivatives into the functional being minimized; and multiplying the emission error covariance matrix by weighting factors. Intercomparison of methods for a carbon monoxide inversion over a city shows that even though all methods diminish the co-localization problem and produce similar general patterns, detailed information can greatly change according to the method used ranging from smooth, isotropic and short range modifications to not so smooth, non-isotropic and long range modifications. Poisson (non-Gaussian) and Gaussian assumptions both show these patterns, but for the Poisson case the emissions are naturally restricted to be positive and changes are given by means of multiplicative correction factors, producing results closer to the true nature of emission errors. Finally, we propose and test a new two-step, two-scale, fully Bayesian approach that deals with the co-localization problem and can be implemented for any prior density distribution.

Description: ABSTRACT Size-resolved aerosol number and mass concentrations and the mixing ratios of O 3 and various trace gases were continuously measured at an urban station before and during the Beijing Olympic and Paralympic Games (June 5 to September 22, 2008). Twenty-three new particle formation (NPF) events were identified; these usually were associated with changes in wind direction and/or rising concentrations of gas-phase precursors or after precipitation events. Most of the NPF events started in the morning and continued to noon as particles in the nucleation mode grew into the Aitken mode. From noon to midnight, the aerosols grew into the accumulation mode through condensation and coagulation. Ozone showed a gradual rise starting around 10:00 local time, reached its peak around 15:00, and then declined as the organics increased. The dominant new particles species were organics (40 to 75% of PM 1 ) and sulphate; nitrate and ammonium were more minor contributors.

Description: ABSTRACT This paper provides an account of the performance of a multimodel ensemble for real time forecasts of Atlantic tropical cyclones during 2004, 2005 and 2006. The Florida State University (FSU) superensemble is based on a suite of model forecasts and the interpolated official forecast that were received in real time at the National Hurricane Center. The FSU superensemble is a multimodel ensemble that utilizes forecasts from the member models by removing their individual biases based on a recent past history of their performances. This superensemble carries separate statistical weights for track and intensity forecasts for every six hours of the member model forecasts. The real time results from 2004 show an improvement up to 15% for track forecasts and up to 11% for intensity forecasts for the superensemble compared to other models and consensus aids. During 2005, the superensemble intensity performance was best for most lead times. The consistency of the superensemble forecasts of track are also illustrated for several storms of 2004 season. The superensemble methodology produced impressive intensity forecasts for Rita and Wilma during 2005. The study shows the capability of the superensemble in predicting rapidly intensifying storms when most member models failed to capture their strengthening.

Description: ABSTRACT Micrometeorological measurements of aerosol sized dry particle deposition velocity ( V d ) onto forested canopies have significantly advanced over the past 2 decades and now include both – airborne and stationary platforms. However, the interpretation of these V d measurements still relies on stationary and planar homogeneous flow assumptions only appropriate to flat-terrain conditions. Simplified model calculations were used to examine how variations in hill height ( H ) introduce biases in V d when assumptions appropriate to flat terrain are applied to periodic and gentle 2D cosine topography covered with tall and dense forested canopies. It was shown that increasing H reduced the variability in V d for all aerosol sized particle diameters ( d p ) inside the canopy when the hill slope ( H/L ) remained constant (= 0.1), where L is the cosine hill half-length. At the landscape scale, as may be monitored from airborne platforms, assumptions appropriate to flat-terrain appear accurate with increasing H for a constant and gentle H/L (= 0.1). Inside the canopy, variability in V d tends to be larger than above the canopy for all H values and d p classes.

Description: ABSTRACT The present study investigated the diurnal cycle of precipitation in Sweden using hourly ground observations for 1996–2008. General characteristics of phase and amplitude for the diurnal cycle of precipitation, both in amount and frequency, were identified. In the warm season (April to September), the ‘typical’ afternoon (14–16 LST) peaks are dominant over inland Sweden, whereas late night to early morning (04–06 LST) peaks with relatively weak amplitude are discernable in the east coast along the Baltic Sea. The diurnal variation is almost negligible in the cold season (October to March), due to the weak solar radiation at high-latitudes. The variation of convective activity forced by solar heating and modulated by geographical characteristics were suggested as primarily factors to invoke the cycles and spatial variation identified. The observed cycle was compared with the cycle simulated by a regional climate model. The model fairly well captures the spatial pattern of the phase of the diurnal cycle. However, the warm season afternoon peak is simulated too early and too uniformly across the stations, associated with too frequent occurrences of convective rainfall events with relatively light intensity. These discrepancies point to the need to improve the convection parameterization and geographic representation of the model.

Description: ABSTRACT The thaw and release of carbon currently frozen in permafrost will increase atmospheric CO 2 concentrations and amplify surface warming to initiate a positive Permafrost Carbon Feedback (PCF) on climate. We use surface weather from three Global Climate Models based on the moderate warming, A1B Intergovernmental Panel on Climate Change emissions scenario and the SiBCASA land surface model to estimate the strength and timing of the PCF and associated uncertainty. By 2200, we predict a 29–59% decrease in permafrost area and a 53–97 cm increase in active layer thickness. By 2200, the PCF strength in terms of cumulative permafrost carbon flux to the atmosphere is 190 ± 64 Gt C. This estimate may be low because it does not account for amplified surface warming due to the PCF itself and excludes some discontinuous permafrost regions where SiBCASA did not simulate permafrost. We predict that the PCF will change the Arctic from a carbon sink to a source after the mid 2020s and is strong enough to cancel 40–88% of the total global land sink. The thaw and decay of permafrost carbon is irreversible and accounting for the PCF will require larger reductions in fossil fuel emissions to reach a target atmospheric CO 2 concentration.

Description: ABSTRACT During the period around the Beijing 2008 Olympic Games, the Beijing 2008 Olympics Research and Development Project (B08RDP) was conducted as part of the World Weather Research Program short-range weather forecasting research project. Mesoscale ensemble prediction (MEP) experiments were carried out by six organizations in near real-time, in order to share their experiences in the development of MEP systems. The purpose of this study is to objectively verify these experiments and to clarify the problems associated with the current MEP systems through the same experiences. Verification was performed using the MEP outputs interpolated into a common verification domain with a horizontal resolution of 15 km. For all systems, the ensemble spreads grew as the forecast time increased, and the ensemble mean improved the forecast errors compared with individual control forecasts in the verification against the analysis fields. However, each system exhibited individual characteristics according to the MEP method. Some participants used physical perturbation methods. The significance of these methods was confirmed by the verification. However, the mean error (ME) of the ensemble forecast in some systems was worse than that of the individual control forecast. This result suggests that it is necessary to pay careful attention to physical perturbations.

Description: ABSTRACT The ETKF rescaling scheme has been implemented into the HIRLAM forecasting system in order to estimate the uncertainty of the model state. The main purpose is to utilize this uncertainty information for modelling of flow-dependent background error covariances within the framework of a hybrid variational ensemble data assimilation scheme. The effects of rank-deficiency in the ETKF formulation is explained and the need for variance inflation as a way to compensate for these effects is justified. A filter spin-up algorithm is proposed as a refinement of the variance inflation. The proposed spin-up algorithm will also act to prevent ensemble collapse since the ensemble will receive “fresh blood” in the form of additional perturbation components, generated on the basis of a static background error covariance matrix. The resulting ETKF-based ensemble perturbations are compared with ensemble perturbations based on targeted singular vectors and are shown to have more realistic spectral characteristics.

Description: ABSTRACT An Arctic Ocean with less sea ice and more open water in September has led to anomalous warming of the overlying atmosphere in autumn. Through influences on column water vapor and atmospheric circulation, it is reasonable to expect that this warming will have impacts on Arctic precipitation. Analysis of data from the JRA-25 atmospheric reanalysis reveals an autumn increase in cyclone associated precipitation over the past decade. This is linked to a shift in atmospheric circulation towards more frequent and more intense cyclones in the Atlantic sector of the Arctic. Composites based on years with the five lowest and five highest September ice extents reveal more autumn cyclone associated precipitation and column water vapor during low ice years than during high ice years. However, difficulties in establishing cause and effect, including the absence of a clear association between spatial patterns of recent precipitation changes and ice extent anomalies, lead us to conclude that attribution of recent autumn precipitation increases to reduced ice cover is premature.

Description: ABSTRACT The common derivation of Rossby waves is based on the quasi-geostrophic approximation. A simple non-harmonic approximation for extratropical Rossby waves on the sphere is proposed, in which the meridional coordinate is a parameter instead of a continuous variable. It is shown that, in contrast to the quasi-geostrophic solution, to first order the meridional structure of these non-harmonic Rossby waves becomes irrelevant for determining the dispersion relation in this theory. The proposed approximation accurately reproduces numerical results obtained from runs of an ocean general circulation model initiated from several initial meridional structures and captures the latitudinal dependence of the phase speed of these waves. The proposed theory yields explicit expressions for the dispersion relation and for the meridional structure of the waves.

Description: ABSTRACT Ensemble prediction systems (EPS) are an essential part of numerical weather prediction for the provision of probabilistic forecast guidance. The Hungarian Meteorological Service has implemented a limited area EPS (called ALADIN HUNEPS) based on the ALADIN mesoscale limited area model coupled to the French global ARPEGE EPS (PEARP). The dynamical downscaling method is assessed in terms of ensemble verification scores taking also into account the recent upgrade of the PEARP global system. The verification results point towards some weaknesses of the ALADIN HUNEPS, mainly with respect to the near-surface parameters. Therefore, some improvements are needed so as to provide better and more reliable ensemble predictions for the Carpathian Basin. The application of near-surface perturbations into the surface data assimilation scheme is implemented and tested. The first results show that the surface perturbation method slightly improves the ALADIN HUNEPS, however, further experiments should be made to find out the optimal settings of the method for definite robust improvements of ALADIN HUNEPS.

Description: ABSTRACT Reproduction of daily maximum and minimum temperatures, including tails of their distributions and links to large-scale circulation, is evaluated in an ensemble of high-resolution regional climate model (RCM) simulations over the Czech Republic. RCM data for recent climate (1961–1990) are validated against observed data gridded from a high-density station network. We find large biases in mean monthly temperatures and in seasonal extremes, which are significant in most RCMs throughout the year. The results suggest that an RCM's formulation plays a much more important role in summer, whereas in winter RCM performance is closely linked to the driving GCM. Biases are usually larger for extremes than central parts of temperature distributions, and RCMs tend to underestimate the severity of extremes in both seasons. Substantial underestimation of diurnal temperature range throughout the year in all RCMs and a shift of maximum in its annual cycle suggest general errors in simulating climate processes affecting the difference between daytime and night-time temperatures. Some features of the temperature biases in RCMs are related to deficiencies in the simulation of atmospheric circulation, particularly too strong advection and overestimation of westerly flow at the expense of easterly flow in most RCMs. The general biases in simulating anticyclonic, cyclonic and straight flow also contribute to the underestimated diurnal temperature range.

Description: ABSTRACT The study investigates and compares various methods that aim to diagnose Rossby wave trains with the help of Hovmöller diagrams. Three groups of methods are distinguished: The first group contains trough-and-ridge Hovmöller diagrams of the meridional wind; they provide full phase information, but differ in the method for latitudinal averaging or weighting. The second group aims to identify Rossby wave trains as a whole, discounting individual troughs and ridges. The third group contains diagnostics which focus on physical mechanisms during the different phases of a Rossby wave train life cycle; they include the analysis of eddy kinetic energy and methods for quantifying Rossby wave breaking. The different methods are analysed and systematically compared with each other in the framework of a two-month period in fall 2008. Each method more or less serves its designed purpose, but they all have their own strengths and weaknesses. Notable differences between the individual methods render an objective identification of a Rossby wave train somewhat elusive. Nevertheless, the combination of several techniques provides a rather comprehensive picture of the Rossby wave train life cycle, being broadly consistent with the expected behaviour from previous theoretical analysis.

Description: ABSTRACT Current climate models produce quite heterogeneous projections for the responses of precipitation extremes to future climate change. To help understand the range of projections from multi-model ensembles, a series of idealized “aquaplanet” Atmospheric General Circulation Model (AGCM) runs have been performed with the Community Atmosphere Model CAM3. These runs have been analyzed to identify the effects of horizontal resolution on precipitation extreme projections under two simple global warming scenarios. We adopt the aquaplanet framework for our simulations in order to remove any sensitivity to the spatial resolution of external inputs and to focus on the roles of model physics and dynamics. Results show that a uniform increase of sea surface temperature (SST) and an increase of low-to-high latitude SST gradient both lead to increase of precipitation and precipitation extremes for most latitudes. The perturbed SSTs generally have stronger impacts on precipitation extremes than on mean precipitation. Horizontal model resolution strongly affects the global warming signals in the extreme precipitation in tropical and subtropical regions but not in high latitude regions. This study illustrates that the effects of horizontal resolution have to be taken into account to develop more robust projections of precipitation extremes.

Description: ABSTRACT The advection-diffusion equations defining control volume conservation laws in micrometeorological research are analyzed to resolve discrepancies in their appropriate scalar variables for heat and mass transport. A scalar variable that is conserved during vertical motions enables the interpretation of turbulent mixing as “diffusion”. Gas-phase heat advection is shown to depend on gradients in the potential temperature (θ), not the temperature ( T ). Since conduction and radiation depend on T , advection-diffusion of heat depends on gradients of both θ and T . Conservation of θ (the 1 st Law of Thermodynamics) requires including a pressure covariance term in the definition of the turbulent heat flux. Mass advection and diffusion are universally agreed to depend directly on gradients in the gas “concentration” ( c ), a nonetheless ambiguous term. Depending upon author, c may be defined either as a dimensionless proportion or as a dimensional density, with nontrivial differences for the gas phase. Analyses of atmospheric law, scalar conservation and similarity theory demonstrate that mass advection-diffusion in gases depends on gradients, not in density but rather in a conserved proportion. Flux-tower researchers are encouraged to respect the meteorological tradition of writing conservation equations in terms of scalar variables that are conserved through simple air motions.

Description: ABSTRACT The ensemble Kalman filter (EnKF) is susceptible to losing track of observations, or “diverging”, when applied to large chaotic systems such as atmospheric and ocean models. Past studies have demonstrated the adverse impact of sampling error during the filter's update step. We examine how system dynamics affect EnKF performance, and whether the absence of certain dynamical features in the ensemble may lead to divergence. The EnKF is applied to a simple chaotic model, and ensembles are checked against singular vectors of the tangent linear model, corresponding to short-term growth, and Lyapunov vectors, corresponding to long-term growth. Results show that the ensemble strongly aligns itself with the subspace spanned by unstable Lyapunov vectors. Furthermore, the filter avoids divergence only if the full linearized long-term unstable subspace is spanned. However, short-term dynamics also become important as nonlinearity in the system increases. Non-linear movement prevents errors in the long-term stable subspace from decaying indefinitely. If these errors then undergo linear intermittent growth, a small ensemble may fail to properly represent all important modes, causing filter divergence. A combination of long and short-term growth dynamics are thus critical to EnKF performance. These findings can help in developing practical robust filters based on model dynamics.

Description: ABSTRACT Conditional nonlinear optimal perturbation (CNOP), which is a natural extension of the linear singular vector into the nonlinear regime, has been suggested to identify data sensitive regions in the adaptive observation strategy. CNOP is the global maximum of a cost function, whereas, local CNOP is the local maximum of the cost function if the local maximum exists. The potential application of CNOPs to tropical cyclone adaptive observation is researched. The CNOPs and the first singular vector (FSV) are numerically obtained by a spectral projected gradient algorithm with the Weather Research Forecasting (WRF) model. This paper examines two tropical cyclone cases, a fast straight moving typhoon Matsa (2005) and a slow moving recurving typhoon Shanshan (2006). The CNOPs and FSVs are obtained using the norms of background error at initial time and total dry energy at final time with a 36-h optimization time interval. The spatial structures of CNOPs, their energies, nonlinear evolutions and impacts on track simulations are compared with those of the FSVs. The results show that both the CNOPs and the FSVs are localized, and evolve into the verification area at the final time with the up-scale growth of perturbations. However, the CNOPs are different from the FSVs in spatial patterns, wind maximum distribution, growth rate of energy and impact on track simulation. Compared to FSV, CNOP and local CNOP have greater impact on the forecast in the verification region at the final time in terms of total energy, and have larger, at least similar impact on track simulation too. This indicates the CNOP method with constraint of the norm of background error at initial time and total energy norm at final time is a reasonable candidate in tropical cyclone adaptive observation. Therefore both CNOP and local CNOP are suggested to be considered in tropical cyclone adaptive observation.

Description: ABSTRACT One key question regarding current climate models is whether the projection of climate extremes converges to a realistic representation as the spatial and temporal resolutions of the model are increased. Ideally the model extreme statistics should approach a fixed distribution once the resolutions are commensurate with the characteristic length and time scales of the processes governing the formation of the extreme phenomena of interest. In the current study, a series of AGCM runs with idealized “aquaplanet-steady-state” boundary conditions have been performed with the Community Atmosphere Model CAM3 to investigate the effect of horizontal resolution on climate extreme simulations. The use of the aquaplanet framework highlights the roles of model physics and dynamics and removes any apparent convergence in extreme statistics due to better resolution of surface boundary conditions and other external inputs. Assessed at a same large spatial scale, the results show that the horizontal resolution and time step have strong effects on the simulations of precipitation extremes. The horizontal resolution has a much stronger impact on precipitation extremes than on mean precipitation. Updrafts are strongly correlated with extreme precipitation at tropics at all the resolutions, while positive low-tropospheric temperature anomalies are associated with extreme precipitation at mid-latitudes.

Description: ABSTRACT Utilities of the spectral formulations for measuring information content from observations are explored and demonstrated with real radar data. It is shown that the spectral formulations can be used (i) to precisely compute the information contents from one-dimensional radar data uniformly distributed along the radar beam, (ii) to approximately estimate the information contents from two-dimensional radar observations non-uniformly distributed on the conical surface of radar scan, and thus (iii) to estimate the information losses caused by super-observations generated by local averaging with a series of successively coarsened resolutions to find an optimally coarsened resolution for radar data compression with zero or near-zero minimal loss of information. The results obtained from the spectral formulations are verified against the results computed accurately but costly from the singular-value formulations. As the background and observation error power spectra can be derived analytically for the above utilities, the spectral formulations are computationally much more efficient and affordable than the singular-value formulations, even and especially when the background space and observation space are both extremely large and too large to be computed by the singular-value formulations.

Description: ABSTRACT The particle linear depolarization ratio δ p of Saharan dust, marine aerosols and mixtures of biomass-burning aerosols from southern West Africa and Saharan dust was determined at three wavelengths with three lidar systems during the SAharan Mineral dUst experiMent 2 at the airport of Praia, Cape Verde, between 22 January and 9 February 2008. The lidar ratio S p of these major types of tropospheric aerosols was analysed at two wavelengths. For Saharan dust, we find wavelength dependent mean particle linear depolarization ratios δ p of 0.24–0.27 at 355 nm, 0.29–0.31 at 532 nm and 0.36–0.40 at 710 nm, and wavelength independent mean lidar ratios S p of 48–70 sr. Mixtures of biomass-burning aerosols and dust show wavelength independent values of δ p and S p between 0.12–0.23 and 57–98 sr, respectively. The mean values of marine aerosols range independent of wavelength for δ p from 0.01 to 0.03 and for S p from 14 to 24 sr.

Description: ABSTRACT An aging scheme for black carbon (BC) aerosol was implemented into a regional air-quality forecast model to study the impact of BC aging on air quality predictions. Three different assumptions for the mixing state of BC—external mixture, internal mixture and gradual aging—were used to simulate the distribution of BC particles over North America in April 2002. Cloud –condensation nuclei number and BC wet deposition rate increased significantly and BC mass column loading decreased as a result of BC aging. With the gradual aging process incorporated into the model, the comparison of ground level BC concentration predictions with surface observations was slightly improved. Estimation of the average direct radiative forcing of BC over the spatial domain of this study showed that the factor of direct forcing enhancement by BC aging was much smaller than the mixing state effect factor. The effect of increased wet deposition due to aging compensated partially for the effect of increased absorbance suggesting that the change in the hygroscopic properties of BC due to aging must be taken into account to quantify accurately the effect of BC aging on climate.

Description: ABSTRACT A post-processing method for calibrating probabilistic forecasts of continuous weather variables is presented. The method takes an existing probability distribution and adjusts it such that it becomes calibrated in the long run. The original probability distributions can be ones such as are generated from an NWP ensemble combined with a description of how uncertainty is represented by this ensemble. The method uses a calibration function to relabel raw cumulative probabilities into calibrated cumulative probabilities based on where past observations verified on past raw probability forecasts. Applying the calibration method to existing probabilistic forecasts can be beneficial in cases where the underlying assumptions used to construct the probabilistic forecast are not in line with nature's generating process of the ensemble and corresponding observation. The method was tested on a forecast dataset with five different forecast variables and was verified against the corresponding analyses. The calibration method reduced the calibration deficiency of the forecasts down to the level expected for perfectly calibrated forecasts. When the raw forecasts exhibited calibration deficiencies, the calibration method improved the ignorance score significantly. It was also found that the ensemble-uncertainty model used to create the original probability distribution affected the ignorance score.

Description: ABSTRACT We have examined the atmospheric water cycle of both Polar Regions, polewards of 60°N and 60°S, using the ERA-Interim re-analysis and high-resolution simulations with the ECHAM5 model for both the present and future climate based on the IPCC, A1B scenario. The annual precipitation in ERA-Interim amounts to ∼17000 km 3 and is more or less the same in the Arctic and the Antarctic, but it is composed differently. In the Arctic the annual evaporation is ∼8000 km 3 but ∼3000 km 3 less in the Antarctica where the net horizontal transport is correspondingly larger. The net water transport of the model is more intense than in ERA-Interim, in the Arctic the difference is 2.5% and in the Antarctic it is 6.2%. Precipitation and net horizontal transport in the Arctic has a maximum in August and September. Evaporation peaks in June and July. The seasonal cycle is similar in Antarctica with the highest precipitation in the austral autumn. The largest net transport occurs at the end of the major extra-tropical storm tracks in the Northern Hemisphere such as the eastern Pacific and eastern north Atlantic. The variability of the model is virtually identical to that of the re-analysis and there are no changes in variability between the present climate and the climate at the end of the 21 st century when normalized with the higher level of moisture. The changes from year to year are substantial with the 20 and 30-year records being generally too short to identify robust trends in the hydrological cycle. In the A1B climate scenario the strength of the water cycle increases by some 25% in the Arctic and by 19% in the Antarctica, as measured by annual precipitation. The increase in the net horizontal transport is 29% and 22% respectively, and the increase in evaporation correspondingly less. The net transport follows closely the Clausius-Clapeyron relation. There is a minor change in the annual cycle of the Arctic atmospheric water cycle with the maximum transport and precipitation occurring later in the year. There is a small imbalance of some 4–6% between the net transport and precipitation minus evaporation. We suggest that this is mainly due to the fact that the transport is calculated from instantaneous 6-hourly data while precipitation and evaporation is accumulated over a 6 hour period. The residual difference is proportionally similar for all experiments and hardly varies from year to year.

Description: ABSTRACT Annual air-sea exchange of CO 2 in Young Sound, NE Greenland was estimated using p CO 2 surface-water measurements during summer 2006 to 2009 and during an ice-covered winter 2008. All surface p CO 2 values were below atmospheric levels indicating an uptake of atmospheric CO 2 . During sea ice formation, dissolved inorganic carbon (DIC) content is reduced causing sea ice to be under saturated in CO 2 . Approximately 1% of the DIC forced out of growing sea ice was released into the atmosphere while the remaining 99% was exported to the underlying water column. Sea ice covered the fjord nine months a year and thereby efficiently blocked air-sea CO 2 exchange. During sea ice melt, dissolution of CaCO 3 combined with primary production and strong stratification of the water column acted to lower surface-water p CO 2 levels in the fjord. Also, a large input of glacial melt water containing geochemically reactive carbonate minerals may contribute to the low surface-water p CO 2 levels. The average annual uptake of atmospheric CO 2 was estimated at 2.7 mol CO 2 m −2 yr −1 or 32 g C m −2 yr −1 for the study area, which is lower than estimates from the Greenland Sea. Variability in duration of sea ice cover caused significant year-to-year variation in annual gas exchange.

Description: ABSTRACT The aerosol climatology at the coastal Antarctic Neumayer Station (NM) was investigated based on continuous, 25 years long observations of biogenic sulfur components (methanesulfonate and non sea salt sulfate), sea salt and nitrate. Whilst significant long-term trends could only be detected for nitrate (-3.6±2.5% per year between 1983 and 1993 and +4.0±3.2% per year from 1993–2007), non-harmonic periodicities between 2 and 5 years were typical for all species. Dedicated time series analyses revealed that relations to sea ice extent and various circulation indices are weak at best or not significant. In particular, no consistent link between sea ice extent and sea salt loadings was evident suggesting only a rather local relevance of the NM sea salt record. Nevertheless, a higher Southern Annular Mode index tended to entail a lower biogenic sulfur signal. In examining the spatial uniformity of the NM findings we contrasted them to respective 17 years records from the coastal Dumont d’Urville Station (DDU). We found similar long term trends for nitrate, indicating an Antarctic-wide but not identifiable atmospheric signal, though any significant impact of solar activity or pollution could be ruled out. No inter-site variability on the multi annual scale was evident for the other ionic compounds.

Description: ABSTRACT In this paper, an ensemble 4DVar (referred to as PODEn4DVar) is proposed on the basis of the proper orthogonal decomposition (POD) and ensemble forecasting techniques. The ensemble forecasts are conducted to obtain the model perturbations (MPs) and their corresponding observation perturbations (OPs). Under the assumption of the linear relationship between the MPs and the OPs, the POD transformation is applied to the OP space rather than the MP space directly, which substantially decreases the computational costs. The optimal MP and its corresponding OPs is thus represented by the transformed MP ensemble and their related OP orthogonal base vectors to fit the 4-D observation innovations in the assimilation window. Further, the implementation of the forecast model ensemble update is successfully implemented by replacing the single 4-D observation innovation with the ensemble of innovation vectors. The feasibility and effectiveness of the PODEn4DVar are demonstrated in an idealized model with simulated observations. It is found that the PODEn4DVar is capable of outperforming both 4DVar and the EnKF under both perfect and imperfect-model scenarios with lower computational costs compared with EnKF.

Description: ABSTRACT This paper focuses on the application of a simple analytical parameterization to the filling of the Ultraviolet Index (UVI) data gaps, and the reconstruction of past UVI values at Badajoz and Cáceres (Southwestern Spain). The empirical model involves three independent variables: the solar zenith angle, the total ozone column and the clearness index. Regarding the first application, daily UVI was estimated for more than 30 days when UV measurements were not available in 2007. For these cases, the missing UVI data were replaced by estimated values, thus affecting the UVI annual mean and median. Regarding the second application, the reconstruction of past UVI time series (1950–2000) is performed only for clear-sky cases (cloud and aerosol free conditions) using the COST 726 total ozone climatology. The linear UVI trends for two periods (1957–1978, and 1979–2000) are calculated for summer months using linear least squares fits. Both locations show statistically significant UVI trends for the most recent period 1979–2000, with values of (+4.4±1.6) percent per decade for Badajoz, and (+4.9±1.8) percent per decade for Cáceres. This result is mainly driven by the ozone decline at northern mid-latitudes during this period. No significant trend is found for the other analyzed period.

Description: ABSTRACT The operational performance and usefulness of regional climate models at seasonal time scales are assessed by downscaling an ensemble of global seasonal forecasts. The Rossby Centre RCA regional model was applied to downscale a 5-members ensemble from the ECMWF System3 global model in the European Atlantic domain for the period 1981–2001. One-month lead time global and regional precipitation predictions were compared over Europe—and particularly over Spain—focusing the study in SON (Autumn) dry events. A robust tercile-based probabilistic validation approach was applied to compare the forecasts from global and regional models, obtaining significant skill in both cases, but over a wider area for the later. Finally, we also analyze the performance of a mixed ensemble combining both forecasts.

Description: ABSTRACT The trends of terrestrial carbon exchange and their mechanistic drivers are key components in understanding how carbon reservoirs will respond to climate change. Here we show trends in seasonal non-fossil land-atmosphere carbon exchange from 1980 to 2008 using atmospheric CO 2 inversion results. Four indices were analyzed: growing-season net flux (GSNF), dormant-season net flux (DSNF), amplitude and annual net carbon flux (NCF). We find that the global land carbon sink is intensifying at −0.057 ± 0.01 PgC yr −2 , resulting in −1.65 ± 0.29 PgC of additional uptake over the period examined. This increased total land uptake is driven by a decline in the DSNF (−0.04 ± 0.01 PgC yr −2 ) and intensification of the GSNF (−0.02 ± 0.008 PgC yr −2 ). Regional analysis shows the dominant role of the southern half of the African continent; intensification of the GSNF (−0.02 ± 0.005 PgC yr −2 ) and a decline in the DSNF (−0.013 ± 0.004 PgC yr −2 ) imply that Africa has shifted from a net carbon source in the 1980s to near-neutral emissions. By contrast, a weakening of the GSNF is found in temperate North America (0.015 ± 0.007 PgC yr −2 ) and tropical America (0.01 ± 0.005 PgC yr −2 ).

Description: ABSTRACT Extensive lidar measurements of Saharan dust and biomass–burning smoke were performed with one airborne and three ground–based instruments in the framework of the second part of the SAharan Mineral dUst experiMent (SAMUM-2a) during January and February of 2008 at Cape Verde. Further lidar observations with one system only were conducted during May and June of 2008 (SAMUM-2b). The active measurements were supported by Sun photometer observations. During winter, layers of mineral dust from the Sahara and biomass–burning smoke from southern West Africa pass Cape Verde on their way to South America while pure dust layers cross the Atlantic on their way to the Caribbean during summer. The mean 500-nm aerosol optical thickness (AOT) observed during SAMUM-2a was 0.35 ± 0.18. SAMUM-2a observations showed transport of pure dust within the lowermost 1.5 km of the atmospheric column. In the height range from 1.5–5.0 km, mixed dust/smoke layers with mean lidar ratios of 67 ± 14 sr at 355 and 532 nm, respectively, prevailed. Within these layers, wavelength–independent linear particle depolarization ratios of 0.12–0.18 at 355, 532, and 710 nm indicate a large contribution (30%–70%) of mineral dust to the measured optical properties. Ångström exponents for backscatter and extinction of around 0.7 support this finding. Mean extinction coefficients in the height range between 2 and 4 km were 66 ± 6 Mm −1 at 355 nm and 48 ± 5 Mm −1 at 532 nm. Comparisons with airborne high–spectral–resolution lidar observations show good agreement within the elevated layers. 3–5 km deep dust layers where observed during SAMUM-2b. These layers showed optical properties similar to the ones of SAMUM-1 in Morocco with a mean 500-nm AOT of 0.4 ± 0.2. Dust extinction coefficients were about 80 ± 6 Mm −1 at 355 and 532 nm. Dust lidar ratios were 53 ± 10 sr at 355 and 532 nm, respectively. Dust depolarization ratios showed an increase with wavelength from 0.31 ± 0.10 at 532 nm to 0.37 ± 0.07 at 710 nm.

Description: ABSTRACT Size resolved aerosol and gas fluxes were measured in Stockholm from 1 April 2008 to 15 April 2009 over both urban and green sectors. CO 2 and H 2 O fluxes peaked in daytime for all seasons. CO 2 concentrations peaked in winter. Due to vegetation influence the CO 2 fluxes had different diurnal cycles and magnitude in the two sectors. In the urban sector, CO 2 fluxes indicated a net source. The sector dominated by residential areas and green spaces had its highest aerosol fluxes in winter. In spring, super micrometer concentrations for both sectors were significantly higher, as were the urban sector rush hour fluxes. The sub micrometer aerosol fluxes had a similar diurnal pattern with daytime maxima for all seasons. This suggest that only the super micrometer aerosol emissions are dependent on season. During spring there was a clear difference in super micrometer fluxes between wet and dry streets. Our direct flux measurements have improved the understanding of the processes behind these aerosol emissions. They support the hypothesis that the spring peak in aerosol emissions are due to road dust, produced during the winter, but not released in large quantities until the roads dry up during spring, and explain why Stockholm has problems meeting the EU directive for aerosol mass (PM 10 ).

Description: ABSTRACT A large field experiment of the Saharan Mineral Dust Experiment (SAMUM) was performed in Praia, Cape Verde, in January and February 2008. The aerosol at Praia is a superposition of mineral dust, sea-salt, sulfates, and soot. Particles smaller than 500nm are mainly mineral dust, mineral dust-sulfate-mixtures, sulfates, and soot-sulfate-mixtures. Particles larger then 2.5 μm consist of mineral dust, sea-salt, and few mineral dust-sulfate-mixtures. A transition range exists in between. The major internal mixtures are mineral dust-sulfate and soot-sulfate. Mineral dust-sea-salt mixtures occur occasionally, mineral dust-soot mixtures were not observed. The aspect ratio was 1.3–1.4 for dry particles smaller than 500 nm and 1.6–1.7 for larger ones. Parameterizations are given for dry and humid state. While the real part of the refractive index showed low variation (1.55–1.58 at 532 nm), a multi-modal imaginary part was detected as function of particle size, reflecting the complex composition. Soot mainly influences the absorption for wavelengths longer than the hematite absorption edge, while for shorter wavelengths dust is dominating. The refractive index of the aerosol depends on the source region of the mineral dust and on the presence/absence of a marine component.

Description: ABSTRACT In the framework of the Saharan Mineral Dust Experiment (SAMUM) in 2008 the mixing of the urban pollution plume of Dakar (Senegal) with mineral dust was studied in detail using the German research aircraft Falcon which was equipped with a nadir-looking High Spectral Resolution Lidar (HSRL) and extensive aerosol in-situ instrumentation. The mineral dust layer as well as the urban pollution plume were probed remotely by the HSRL and in-situ. Back trajectory analyses were used to attribute aerosol samples to source regions. We found out that the emission from the region of Dakar increased the AOD (532 nm) from approx. 0.30 over sea and over land east of Dakar to 0.35 in the city outflow. In the urban area, local black carbon (BC) emissions, or soot respectively, contributed more than 75% to aerosol absorption at 530 nm. In the dust layer the single-scattering albedo at 530 nm was 0.96–0.99, while we found a value of 0.908 ± 0.018 for the aerosol dominated by urban pollution. After 6h of transport over the North Atlantic, the externally mixed mode of secondary aerosols had almost completely vanished, while the black carbon agglomerates (soot) were still externally mixed with mineral dust particles.

Description: ABSTRACT We applied and compared bottom-up (process model-based) and top-down (atmospheric inversion-based) scaling approaches to evaluate the spatial and temporal patterns of net ecosystem production (NEP) over a 2.5·10 5 km 2 area (the state of Oregon) in the western United States. Both approaches indicated a carbon sink over this heterogeneous region in 2003 (a relatively warm, dry year in western Oregon) and 2007 (near normal), with carbon uptake primarily in forested and agricultural areas. The statewide mean NEP for 2007 using the bottom-up approach was 80 gC m −2 yr −1 , which compares with 145 gC m −2 yr −1 for the top-down approach. Seasonality of daily NEP at the ecoregion scale showed similar patterns across the two approaches, but with less sensitivity to seasonal drought in the top-down model. In 2003, simulated annual NEP was lower than in 2007 for both scaling approaches, but the reduction was stronger with the bottom-up approach. Estimates of mean NEP on forested lands from a forest inventory approach, and from the CarbonTracker inversion scheme, bracketed that of our bottom-up approach (ratios to bottom-up estimates were 1.3 and 0.3, respectively). These results support the need for a multiple constraint approach to evaluation of regional trace gas budgets.

Description: ABSTRACT The buoyancy flux at the air/sea interface plays a key role in water mass transformation and mixing as it modifies surface water density and in turn drives overturning and enhances stratification. It is the interplay of these two independent heat and freshwater buoyancy flux components that is of central importance when analysing mechanisms of the ocean/atmosphere interaction. Here, a diagnostic quantity (Θ B ) is presented that allows to capture the relative contribution of both components on the buoyancy flux in one single quantity. Using NCEP reanalysis of heat and freshwater fluxes (1948–2009) demonstrates that Θ B , is a convenient tool to analyse both the temporal and spatial variability of their corresponding buoyancy fluxes. For the global ocean the areal extent of buoyancy gain and loss regions changed by 10%, with the largest extent of buoyancy gain during the 1970 to 1990 period. In the subpolar North Atlantic, and likewise in the South Pacific, decadal variability in freshwater flux is pronounced and, for the latter region, takes control over the total buoyancy flux since the 1980's. Some of the areal extent time series show a significant correlation with large-scale climate indices.

Description: ABSTRACT Parameter uncertainty in atmospheric model forcing and closure schemes has motivated both parameter estimation with data assimilation and use of pre-specified distributions to simulate model uncertainty in short-range ensemble prediction. This work assesses the potential for parameter estimation and ensemble prediction by analyzing two months of mesoscale ensemble predictions in which each member uses distinct, and fixed, settings for four model parameters. A space-filling parameter selection design leads to a unique parameter set for each ensemble member. An experiment to test linear scaling between parameter distribution width and ensemble spread shows the lack of a general linear response to parameters. Individual member near-surface spatial means, spatial variances, and skill show that perturbed models are typically indistinguishable. Parameter-state rank correlation fields are not statistically significant, although the presence of other sources of noise may mask true correlations. Results suggest that ensemble prediction using perturbed parameters may be a simple complement to more complex model-error simulation methods, but that parameter estimation may prove difficult or costly for real mesoscale NWP applications.

Description: ABSTRACT The piecewise potential vorticity (PV) inversion method developed by Davis and Emanuel (1991) is used to diagnose the development processes of a polar low over the Sea of Japan in December 2003. The synoptic scale balanced flows associated with the polar low are successfully captured using the inversion method. It is shown that, antecedent to the development of the polar low, a positive lower-tropospheric temperature anomaly was induced by the approach of a positive tropopause-level PV anomaly over the northern Sea of Japan. The analysis suggests that the polar low was initiated as a result of the combined effect of the positive PV anomaly near the tropopause and the near-surface positive temperature anomaly. The rapid height falls in the lower troposphere were primarily contributed by the upper tropospheric PV anomaly. Further intensification of the polar low was afforded by latent heat release associated with cloud and precipitation processes. After the polar low moved over northern Honshu, quick dissipation was primarily rendered by the thinning and elongating of the upper level PV anomaly that led to a rapid reduction of the lower troposphere height perturbations associated with it.

Description: ABSTRACT Changes in biological productivity in the Southern Ocean have the potential to have a significant effect on world climate. Here we use a combination of satellite, model and model reanalysis data to examine climate variability in the Australian sector of the Southern Ocean (110–160°E, 40–70°S) to identify the controls on chlorophyll- a (a proxy for phytoplankton biomass) and primary productivity and evaluate trends in these controls over the period 1997–2007. In summer, in the 65–70°S zone, sea-ice concentration together with the Southern Annular Mode explains 51% of the variance in chlorophyll- a , while mean wind stress and sea-surface temperature explains 55% of the variance in the 60–65°S zone. Further north, key controls are photosynthetically active radiation, sea-surface temperature, mixed layer depth and stratification. Trends in hydrodynamic variables are found to often be opposite in sign and up to an order of magnitude larger than those previously identified in the same sector for 1958–2005. Allowing for the effect of shorter time series on the magnitude of the trends, many recent trends seem to be outside the range of previous variability. These results are consistent with a shift in the ocean state in the past 10–15 years, in response to a shift in climate.

Description: ABSTRACT Implementations of incremental variational data assimilation require the iterative minimization of a series of linear least-squares cost functions. The accuracy and speed with which these linear minimization problems can be solved is determined by the condition number of the Hessian of the problem. In this study we examine how different components of the assimilation system influence this condition number. Theoretical bounds on the condition number for a single parameter system are presented and used to predict how the condition number is affected by the observation distribution and accuracy and by the specified lengthscales in the background error covariance matrix. The theoretical results are verified in the Met Office variational data assimilation system, using both pseudo-observations and real data.

Description: ABSTRACT The monitoring of conservation properties is essential for model development and for the investigation of the hydrological cycle. This is especially relevant for models that do not solve equations in flux form and do not apply a finite volume discretisation. The conservation properties of the mesoscale model COSMO are evaluated by using a finite volume diagnostic approach. That is the sub-domain budget of energy, water mass and total mass are diagnosed in a control volume that can be placed at each site in the model domain and is independent of the grid size. Thus, this diagnostic method has the major advantage that it can be applied to realistic simulations. The application of the diagnostic method to the COSMO model reveals a good preservation of the water mass, but large errors in energy and total mass conservation. The analysis shows in which extent errors in the treatment of thermodynamical processes, numerical filters and moisture advection schemes contaminate the sub-domain budgets. In this paper we will show that the application of a saturation adjustment scheme under a fixed volume condition is required for models, which use the non-hydrostatic equations and height-based coordinates. Also, a further extension of the model physics will be introduced and discussed for a realistic test case.

Description: ABSTRACT The new type closed-path CO 2 /H 2 O infrared gas analyzer enables us to calculate CO 2 fluxes from both the mixing ratio ( F c MR ) and mass density of CO 2 ( F c WPL ). After the WPL correction was applied, F c MR and F c WPL were almost in accord with each other. However, F c WPL tended to be slightly larger than F c MR , which resulted in a significant difference in cumulative CO 2 fluxes. We found that this difference was explained by the pressure covariance term, which is normally omitted in the WPL correction. Therefore, ignoring the pressure covariance term in the WPL correction can cause a serious error in estimation of annual net ecosystem exchange. To reduce uncertainties in calculations, we recommend using the mixing ratio for calculation of CO 2 fluxes when using the new type closed-path infrared gas analyzer.

Description: ABSTRACT Primary (i.e., sugars and sugar-alcohols) and secondary (i.e., carboxylic acids) water-soluble organic compounds (WSOCs) in size-segregated aerosols from the urban and mountain atmosphere of China and from the marine atmosphere in the outflow region of East Asia were characterized on a molecular level. Levoglucosan is the most abundant compound among the quantified WSOCs in the urban and mountain atmosphere, whose concentrations at the urban site was 1–2 orders of magnitude higher than that at the mountain and marine sites. In contrast, malic, succinic and phthalic acids were dominant among the measured WSOCs at the marine site. In the urban air sugars except levoglucosan gave a bimodal size distribution with a large peak in fine range (〈2.1 μm) and a small peak in coarse range (≥ 2.1 μm) during winter, being opposite to those in spring. In contrast, these WSOCs at the mountain and marine sites dominated in the coarse range but diminished and even disappeared in the fine range. Geometric mean diameters (GMDs) of the measured WSOCs in the fine mode at the urban site were larger in winter than in spring. Levoglucosan and carboxylic acids except for azelaic and benzoic acids showed a larger GMD in the coarse mode at the marine site probably due to an increased hygroscopic growth.

Description: ABSTRACT Recent developments in applying carbon-isotope information to better understand regional and global methane budgets infer a strong role by a highly-fractionating seasonal sink such as atomic chlorine. Specifically, OH as the predominant seasonal sink cannot account for the ‘phase ellipses’ based on observed seasonal cycles of methane mixing ratio and isotope ratio, δ 13 C. While a strong role by atomic chlorine is inferred empirically, open questions remain about the interplay between sources and sinks in determining the properties of phase ellipses. This paper employs a simple didactic model of the seasonal cycling of atmospheric methane in order to understand such interplay. We demonstrate that a single seasonal sink and seasonal source act together to imprint anti-phase seasonalities on atmospheric methane and δ 13 C, which lead to phase ellipses that collapse onto a straight line with slope characteristic of that sink. This explains empirical findings of these anti-phase relationships in 3-D modeling studies. We also demonstrate that multiple seasonal sinks acting with a seasonal source can yield surprising properties for the phase ellipse that not only explain some features of phase ellipses reported in modeling studies but also have the potential to explain marked inter-annual variation in phase ellipses based on observation.

Description: ABSTRACT The seasonal variability of sea-ice cover in the Southern Ocean is examined using daily sea-ice concentration and ice velocity products for 2003–2009, derived from Advanced Microwave Scanning Radiometer for EOS (AMSR-E) data. This study quantitatively shows the contribution of 1) ice production/reduction within the sea ice, 2) ice production/reduction at the sea-ice edge, and 3) zonal ice transport to the seasonal change of sea-ice area. Area of greatest ice production occurs along the coast of Ross Sea and East Antarctica from March to September. The contribution of zonal transport to the seasonal change of ice area is one order magnitude smaller than local ice production/reduction. Clear regional and seasonal differences are found in the large-scale processes named above. Generally, ice area increases due to ice production, both at the ice edge and within the pack in the autumn and winter. The most significant ice production at the ice edge occurred in the Weddell Sea; the ice production provides 56% of total increase of ice cover in this area. In contrast, moderate ice melting occurs at the ice edge through almost all months in the Indian Ocean sector.

Description: ABSTRACT The impact on snow pack albedo from local elemental carbon (EC) sources in Svalbard has been investigated for the winter of 2008. Highly elevated EC concentrations in the snow are observed around the settlements of Longyearbyen and Svea (locally 〉 1000 ng/g, about 200 times over the background level), while EC concentrations similar to the background level are seen around Ny-Ålesund. Near Longyearbyen and Svea, darkened snow influenced by wind transported coal dust from open coal stockpiles is clearly visible from satellite images and by eye at the ground. As a first estimate, the reduction in snow albedo caused by local EC pollution from the Norwegian settlements has been compared to the estimated reduction caused by long-range transported EC for entire Svalbard. The effect of local EC from Longyearbyen, Svea, and all Norwegian settlements are estimated to 2.1%, 7.9%, and 10% of the total impact of EC, respectively. The EC particles tend to stay on the surface during melting, and elevated EC concentrations due to the spring melt was observed. This accumulation of EC enhances the positive albedo feedbacks. The EC concentrations were observed to be larger in metamorphosed snow than in fresh snow, and especially around ice lenses.

Description: ABSTRACT At the end of January and beginning of February 2006, an extreme precipitation event occurred over Central Norway. The precipitation in addition to warm temperatures produced flooding and landslides that caused considerable damage to infrastructure. The event is explored with conventional data, data from remote sensing and numerical simulations. It is shown that there was very little quasi-geostrophic forcing during the event and that the extreme precipitation is locally generated by strong and persistent winds impinging the mountains. The mountains in the southwestern part of Norway, far away from the precipitation, contributed significantly to the extreme, by blocking, deflection and enhancement of the low level flow. The warm and humid air masses involved are shown to originate in the sub-tropics. Assessment of forecasts with different lead times reveal a sensitivity to a baroclinic system to the east of Newfoundland upstream of the event in Central Norway.

Description: ABSTRACT The second field campaign of the SAharan Mineral dUst experiMent (SAMUM–2) was performed between 15 January and 14 February 2008 at the airport of Praia, Cape Verde, and provided valuable information to study the westward transport of Saharan dust and the mixing with biomass–burning smoke and sea–salt aerosol. Here lidar, meteorological, and particle measurements at Praia, together with operational analyses, trajectories, and satellite and synoptic station data are used to give an overview of the meteorological conditions and to place other SAMUM–2 measurements into a large–scale context. It is demonstrated that wintertime dust conditions at Cape Verde are closely related to the movement and intensification of mid–latitude high–pressure systems and the associated pressure gradients at their southern flanks. These cause dust emission over Mauritania, Mali, and Niger, and subsequent westward transport to Cape Verde within about 1–5 days. Dust emissions often peak around midday, suggesting a relation to daytime mixing of momentum from nocturnal low–level jets to the surface. The dust layer over Cape Verde is usually restricted to the lowest 1.5 km of the atmosphere. During periods with near–surface wind speeds above about 5.5 ms −1 , a maritime aerosol layer develops which often mixes with dust from above. On most days, the middle levels up to about 5 km additionally contain smoke that can be traced back to sources in southern West Africa. Above this layer, clean air masses are transported to Cape Verde with the westerly flow at the southern side of the subtropical jet. The penetration of extra–tropical disturbances to low latitudes can bring troposphere–deep westerly flow and unusually clean conditions to the region.

Description: ABSTRACT Determination of surface reflectance in the red and blue channels is a critical step in retrieving aerosol optical thickness (AOT) from MODIS measurements. The MODIS Collection 005 (C005) aerosol algorithm uses a ratio method to determine the surface reflectance in the red (0.66 μm) and blue (0.47 μm) channels from the surface reflectance in the 2.1 μm channel using global surface reflectance relationships. In this study, we attempted to improve the retrieval of AOT from MODIS measurements using a new surface parameterization derived using ground-based sunphotometer data and 6S radiative transfer code. The estimated surface reflectance in the red, blue, and near-IR channel were used to derive ratio between them for use in the new retrieval from MODIS data. Our results demonstrate that the ratio of surface reflectance in the red and blue channels to the surface reflectance in the 2.1 μm channel varies seasonally in the Xianlin district of Nanjing City, China. These ratios are different from those assumed by the MODIS aerosol algorithm for the retrieval of AOT over land. The use of the appropriate ratio for the study area in a given season significantly improves the accuracy with the absolute error decreased from 0.15 to 0.08 and the relative error reduced from 31% to 17% in retrieving AOT from MODIS data.

Description: ABSTRACT During the course of SAMUM 1 in May and June 2006, airborne samples were collected in southern Morocco at altitudes between 830 and 3340 m above ground. We analysed approximately 22 500 particles of 1–30 μm by automated individual-particle analysis with a scanning electron microscope (SEM) and an energy-dispersive X-ray (EDX) analyser. The major difference between samples is due to the presence and amount of chlorine- and sulphur-bearing particles, pointing to a varying maritime influence and to different degrees of aging. In contrast, the desert dust component is very homogeneous independent of altitude, activated local source area, and dust storm intensity, implying very fast mixing of the entrained dust with a persistent regional background aerosol. Nevertheless, our study reinforces the usefulness of carbonates and palygorskite as ‘compositional fingerprints’ for mineral dust from source areas in northwestern Africa.  The average median aspect ratio of most particle groups is in the range between 1.5 and 1.6. Higher values are found for S- and Cl-dominated particles (except sodium chloride), and internal mixtures of alumosilicates with carbonates or sulphates. Taken together with other studies, a tendency of increasing aspect ratios with longer transport distances can be observed for Saharan dust.

Description: ABSTRACT The effect of a warmer climate on the properties of extra-tropical cyclones is investigated using simulations of the ECHAM5 global climate model at resolutions of T213 (60 km) and T319 (40 km). Two periods representative of the end of the 20 th and 21 st centuries are investigated using the IPCC A1B scenario. The focus of the paper is on precipitation for the NH summer and winter seasons, however results from vorticity and winds are also presented. Similar number of events are identified at both resolutions. There are, however, a greater number of extreme precipitation events in the higher resolution run. The difference between maximum intensity distributions are shown to be statistically significant using a Kolmogorov-Smirnov test. A Generalised Pareto Distribution is used to analyse changes in extreme precipitation and wind events. In both resolutions, there is an increase in the number of extreme precipitation events in a warmer climate for all seasons, together with a reduction in return period. This is not associated with any increased vertical velocity, or with any increase in wind intensity in the winter and spring. However, there is an increase in wind extremes in the summer and autumn associated with tropical cyclones migrating into the extra-tropics.

Description: ABSTRACT Spatial and vertical distributions of aerosol radiative properties over Indian Continental Tropical Convergence Zone (CTCZ) up to 6 km altitude during the pre-monsoon and monsoon seasons of 2008 have been measured and reported for the first time. Inter-seasonal and intra-seasonal comparisons of different aerosol properties below and above the boundary layer are carried out in and among different regions of CTCZ. During pre-monsoon, aerosol layers were found to be present up to altitude as high as 6 km over the Indo-Gangetic Plains and Himalayan foothills. A large increase in absorption coefficients (by 2 to 5 times) near the Himalayan foothills and coastal India than the background values may be attributed to extensive biomass burning as supported by fire counts data. During monsoon, the aerosols were mostly confined to lower troposphere. However, absorbing aerosols were found to rebuild much faster than scattering aerosols after rains. Heating rates were very high over urban city of Bareilly peaking around 2 km during the pre-monsoon. The HR values over urban Kanpur during monsoon were comparable to Bareilly during pre-monsoon. Negligible latitudinal gradient of heating rate from the Himalayan foothill to central India was observed during both the seasons.

Description: ABSTRACT The preparation of perturbed initial conditions to initialize an ensemble of numerical weather forecasts is a crucial task in current Ensemble Prediction Systems (EPSs). Perturbations are added in the places where they are expected to grow faster, in order to provide an envelope of uncertainty along with the deterministic forecast. This work analyzes the influence of large-scale spatial patterns on the growth of small perturbations. Therefore, we compare Lyapunov vector (LV) definitions, used in the initialization of state-of-the-art EPSs, with the so-called characteristic LVs. We test the dynamical behaviour of these LVs in the two-scale Lorenz’96 system. We find that the commonly-used definitions of LVs include non-intrinsic and spurious effects due to their mutual orthogonality. We also find that the spatial locations where the small-scale perturbations are growing are “quantized” by the large-scale pattern. This “quantization” enhances the artificial disposition of the LVs, which is only avoided using the characteristic LVs, an unambiguous basis which may also be of great use in realistic models for assessing or initializing EPSs.

Description: ABSTRACT During the second Saharan Mineral Dust Experiment (SAMUM-2) field campaign, particles with geometric diameters ( d ) between ∼0.1 and 25 μm were collected on board of the Deutsches Zentrum für Luft- und Raumfahrt (German Aerospace Center, DLR) Falcon aircraft. Size, chemical composition and mixing state of aerosols sampled (spatially and vertically resolved) along the West African coastline and in the Cape Verde Islands region were determined by electron microscopy. A pronounced layer structure of biomass-burning aerosol and desert dust was present for all days during the sampling period from 23 January to 6 February. The aerosol composition of the small particles ( d  〈 0.5 μm) was highly variable and in cases of biomass burning strongly dominated by soot with up to 90% relative number abundance. Internal mixtures of soot particles with mineral dust were not detected. Soot was only observed to mix with secondary sulphate. The coarse particles ( d  〉 0.5 μm) were dominated by silicates. In the Cape Verde Islands region mineral dust is well mixed. The determination of source regions by elemental or mineralogical composition was generally not possible, except for air masses which were transported over the Gulf of Guinea. The real part of the refractive index showed little variation. In contrast, the imaginary part strongly depended on the abundance of soot (biomass-burning aerosol) and haematite (mineral dust).

Description: ABSTRACT In the past two types of laboratory experiments have been employed to determine the dependence of H 2 uptake by soils on temperature and moisture: Head space and flow experiments. The former actually measure the rate constant of the H 2 removal from the head space, k H , the latter the uptake rate of H 2 , U H2 , both caused by a given volume of soil. From an analytical solution of the diffusion equation in the soil we derive a mathematical relation between k H and k s , the desired uptake rate constant of H 2 in soil. Another equation relates U H2 with k s . Both types of experiments actually determine the product of k s with Θ a , the air-filled pore volume fraction. k s ·Θ a for eolian sand and loess loam show zero uptake at very low and high moisture contents and a well defined maximum in between. Unlike soil moisture which also acts on the soil properties, the soil temperature, T, acts essentially on the enzyme activity only. Thus k s (T) is directly proportional to k H (T) or U H2 (T) and the data of all experiments can be superimposed by scaling. The resulting average k s (T) shows a broad maximum around 30°C with zero uptake below -20°C and above 80°C.

Description: ABSTRACT Two comprehensive field campaigns were conducted in 2006 and 2008 in the framework of the Saharan Mineral Dust Experiment (SAMUM) project. The relationship between chemical composition, shape morphology, size distribution and optical effects of the dust particles was investigated. The impact of Saharan dust on radiative transfer and the feedback of radiative effects upon dust emission and aerosol transport were studied. Field observations (ground-based, airborne and remote sensing) and modelling results were compared within a variety of dust closure experiments with a strong focus on vertical profiling. For the first time, multiwavelength Raman/polarization lidars and an airborne high spectral resolution lidar were involved in major dust field campaigns and provided profiles of the volume extinction coefficient of the particles at ambient conditions (for the full dust size distribution), of particle-shape-sensitive optical properties at several wavelengths, and a clear separation of dust and smoke profiles allowing for an estimation of the single-scattering albedo of the biomass-burning aerosol. SAMUM–1 took place in southern Morocco close to the Saharan desert in the summer of 2006, whereas SAMUM–2 was conducted in Cape Verde in the outflow region of desert dust and biomass-burning smoke from western Africa in the winter of 2008. This paper gives an overview of the SAMUM concept, strategy and goals, provides snapshots (highlights) of SAMUM–2 observations and modelling efforts, summarizes main findings of SAMUM–1 and SAMUM–2 and finally presents a list of remaining problems and unsolved questions.

Description: ABSTRACT The Adélie Land coastal region of Antarctica is one of the most prominent cyclogenesis regions in the Southern Hemisphere, and is adjacent to the continent's most intense katabatic wind regime. However, the physical mechanisms responsible for cyclogenesis there are not known. A manual analysis of cyclogenesis for the 2003–2005 period using output from the Antarctic Mesoscale Prediction System (AMPS) identifies two primary patterns of cyclogenesis near the Adélie Land coast. For “secondary development” cyclones, enhanced low-level cyclonic vorticity and baroclinicity result from the combination of an existing synoptic-scale cyclone to the west, coastal barrier winds, and katabatic winds. “Lee cyclogenesis” occurs near 152°E on the cyclonic-shear side of the Adélie Land katabatic jet, where a low-level warm potential temperature anomaly sets up a lee trough that becomes mobile with the arrival of upper-level synoptic-scale forcing. The representation of both “secondary development” and “lee cyclogenesis” cyclones in an automated cyclone-tracking scheme is explored, where it is found that the automated scheme overestimates cyclogenesis for this region. The location of the Antarctic coastal cyclogenesis maximum near Adélie Land is due to the unique juxtaposition of the extraordinary katabatic wind regime and dissipating synoptic-scale cyclones to the west.

Description: ABSTRACT Measurements with two Raman-depolarization lidars of the Meteorological Institute of the Ludwig-Maximilians-Universität, München, Germany, performed during SAMUM-2, were used to characterize the planetary boundary layer (PBL) over Praia, Cape Verde. A novel approach was used to determine the volume fraction of dust υ d in the PBL. This approach primarily relies on accurate measurements of the linear depolarization ratio. Comparisons with independent in situ measurements showed the reliability of this approach. Based on our retrievals, two different phases could be distinguished within the measurement period of almost one month. The first (22–31 January 2008) was characterized by high aerosol optical depth (AOD) in the PBL and large υ d 〉 95%. During the second phase, the AOD in the PBL was considerably lower and υ d less than ∼40%. These findings were in very good agreement with ground based in situ measurements, when ambient volume fractions are considered that were calculated from the actual measurements of the dry volume fraction. Only in cases when dust was not the dominating aerosol component (second phase), effects due to hygroscopic growth became important.