ALBERT

Beschreibung: This study presents the outcome of an inverse modeling inter-comparison experiment on the use of total column CO 2 retrievals from GOSAT for quantifying global sources and sinks of CO 2 . Eight research groups submitted inverse modeling results for the first year of GOSAT measurements. Inversions were carried out using only GOSAT data, a combination of GOSAT and surface measurements, and using only surface measurements. As expected, the most robust flux estimates are obtained at large scales (e.g. within 20% of the annual flux at the global scale), and they quickly diverge towards the scale of the sub-continental TRANSCOM regions and beyond (to〉100% of the annual flux). We focus our analysis on a shift in the CO 2 uptake over land from the Tropics towards the Northern Hemisphere Extra tropics of ~1 PgC/yr when GOSAT data are used in the inversions. This shift is largely driven by TRANSCOM regions Europe and Northern Africa, showing, respectively, an increased uptake and release of 0.7 and 0.9 PgC/yr. Inversions using GOSAT data show a reduced gradient between mid latitudes of the Northern Hemisphere and the Tropics, consistent with the latitudinal shift in carbon uptake. However, the reduced gradients degrade the agreement with background aircraft and surface measurements. To narrow the range of inversion-derived flux estimates will require further efforts to understand the differences not only between the retrieval schemes but also between inverse models, as their contributions to the overall uncertainty are estimated to be of similar magnitude.

Beschreibung: The 1,1,1,2-tetrafluoroethane (HFC-134a), an important alternative to CFC-12 in accordance with the Montreal Protocol on Substances that Deplete the Ozone Layer, is a high Global Warming Potential (GWP) greenhouse gas. Here we evaluate variations in global and regional HFC-134a emissions and emission trends, from 1995 to 2010, at a relatively high spatial and temporal (3.75° in longitude × 2.5° in latitude and 8-day) resolution, using surface HFC-134a measurements. Our results show a progressive increase of global HFC-134a emissions from 19 ± 2 Gg/yr in 1995 to 167 ± 5 Gg/yr in 2010, with both a slowdown in developed countries and a 20 %/yr increase in China since 2005. A seasonal cycle is also seen since 2002, which becomes enhanced over time, with larger values during the boreal summer.

Beschreibung: Unprecedented, widespread and devastating hailstorms occurred during February and March 2014 over north peninsular India (study area). A diagnostic study has been carried out to understand the causes for the same. Over the study area the atmosphere was convectively unstable due to the incursion of warm and moist air from Bay of Bengal and Arabian Sea which was overlaid by cold and dry mid-latitude westerlies caused due to the unusual upper oceanic heat content of the Pacific Ocean. At the surface and lower levels, anticyclonic flow over the central India produced easterly winds and cyclonic circulation over Arabian Sea at 850 hPa level produced westerly winds over the peninsular India. Meeting of these winds caused convergence of moist air in the lower levels. The troughs in the upper level westerlies provided the divergence in the upper levels. As a consequence of this convergence/divergence structure, synoptic scale slow rising motion occurred over the study region. This released the convective instability to cause deep and wide convection with cloud bases at ~ 1500 m above mean sea level and tops well above the freezing level. Release of latent heat of deposition of water vapour provided extra buoyancy and produced strong updrafts causing explosive growth of the clouds reaching to very high levels and formation of large hails in the clouds. This atmospheric set up was result of combined effect of planetary and synoptic forcings which persisted for ~3 weeks.

Beschreibung: It has been suggested that the Sun may evolve into a period of lower activity over the 21st century. This study examines the potential climate impacts of the onset of an extreme ‘Maunder Minimum like’ grand solar minimum using a comprehensive global climate model. Over the second half of the 21st century, the scenario assumes a decrease in total solar irradiance of 0.12% compared to a reference RCP8.5 experiment. The decrease in solar irradiance cools the stratopause (~1 hPa) in the annual and global mean by 1.4 K. The impact on global mean near-surface temperature is small (~−0.1 K), but larger changes in regional climate occur during the stratospheric dynamically active seasons. In Northern hemisphere (NH) winter-time, there is a weakening of the stratospheric westerly jet by up to ~3-4 m s 1 , with the largest changes occurring in January-February. This is accompanied by a deepening of the Aleutian low at the surface and an increase in blocking over northernEurope and the north Pacific. There is also an equatorward shift in the Southern hemisphere (SH) midlatitude eddy-driven jet in austral spring. The occurrence of an amplified regional response during winter and spring suggests a contribution froma top-down pathway for solar-climate coupling; this is tested using an experiment in which ultraviolet (200–320 nm) radiation is decreased in isolation of other changes. The results show that a large decline in solar activity over the 21st centurycould have important impacts on the stratosphere and regional surface climate.

Beschreibung: Satellite microwave observations of rain, whether from radar or passive radiometers, depend in a very crucial way on the vertical distribution of the condensed water mass and on the types and sizes of the hydrometeors in the volume resolved by theinstrument. This crucial dependence is non-linear, with different types and orders of non-linearity that are due to differences in the absorption/emission and scattering signatures at the different instrument frequencies. Because it is not monotoneas a function of the underlying condensed water mass, the non-linearity requires great care in its representation in the observation operator, as the inevitable uncertainties in the numerous precipitation variables are not directly convertible intoan additive white uncertainty in the forward-calculated observations. In particular, when attempting to assimilate such data into a cloud-permitting model, special care needs to be applied to describe and quantify the expected uncertainty in the observations operator in order not to turn the implicit white additive uncertainty on the input values into complicated biases in the calculated radiances. One approach would be to calculate the means and covariances of the non-linearly calculated radiances given an a-priori joint distribution for the input variables. This would be a very resource-intensive proposal if performed in real-time. We propose a representation of the observation operator based on performing this moment calculation off-line, with a dimensionality-reduction step to allow for the effective calculation of the observation operator and the associated covariance in real-time during the assimilation. The approach is applicable to other remotely-sensed observation that dependnon-linearly on model variables, including wind vector fields. The approach has been successfully applied to the case of tropical cyclones, where the organization of the system helps in identifying the dimensionality-reducing variables.

Beschreibung: Black carbon (BC) particles emitted from incomplete combustion of fossil fuel and biomass, and deposited on snow and ice, darken the surface and reduce the surface albedo. Even small initial surface albedo reductions may have larger adjusted effects due to snow morphology changes, and changes in the sublimation- and snow melt rate. Most of the literature on the effect of BC on snow surface albedo is based on numerical models, and few in situ field measurements exist to confirm this reduction. Here we present an extensive set of concurrent in situ measurements of spectral surface albedo, BC concentrations in the upper 5-cm of the snow pack, snow physical parameters (grain size and depth), and incident solar flux characteristics from the Arctic. From this dataset (with median BC concentrations ranging from 5 to 137 ng BC per gram of snow) we are able to separate the BC signature on the snow albedo from the natural snow variability. Our measurements show a significant correlation between BC in snow and spectral surface albedo. Based on these measurements, parameterizations are provided, relating the snow albedo, as a function of wavelength, to the equivalent BC content in the snow pack. The term equivalent BC used here is the elemental carbon concentration inferred from the thermo-optical method adjusted for the fraction of non BC constituents absorbing sunlight in the snow. The first parameterization is a simple equation which efficiently describes the snow albedo reduction due to the equivalent BC without including details on the snow or BC microphysics. This can be used in models when a simplified description is needed. A second parameterization, including snow grain size information, shows enhanced correspondence with the measurements. The extracted parameterizations are valid for wavelength bands 400–900 nm, constrained for BC concentrations between 1 and 400 ng g −1 , and for an optically thick snowpack. The parameterizations are purely empirical, and particular focus was on the uncertainties associated with the measurements, and how these uncertainties propagate in the parameterizations. Integrated, the first parameterization (based only on the equivalent BC) gives a broadband (400–900 nm) snow albedo reduction of 0.004 due to 10 ng equivalent BC per gram of snow, while the effect is almost five times larger for BC concentrations one order of magnitude higher. The study shows that the reconstructed albedo from the second parameterization (including information on the snow grain size) corresponds better to the radiative transfer model Snow, Ice, and Aerosol Radiation (SNICAR) albedo than the reconstructed albedo from the first parameterization (excluding grain size information).

Beschreibung: We systematically explore the ability of the Community Atmospheric Model Version 5 (CAM5) to simulate the Madden-Julian Oscillation (MJO), through an analysis of MJO metrics calculated from an 1100-member perturbed parameter ensemble of 5-year simulations with observed sea-surface temperatures. Parameters from the deep convection scheme make the greatest contribution to variance in MJO simulation quality with a much smaller contribution from parameters in the large-scale cloud, shallow convection and boundary layer turbulence schemes. Improved MJO variability results from a larger lateral entrainment rate and a reduction in the precipitation efficiency of deep convection that was achieved by a smaller auto-conversion of cloud to rain water and a larger evaporation of convective precipitation. Unfortunately, simulations with an improved MJO also have a significant negative impact on the climatological values of low-level cloud and absorbed shortwave radiation, suggesting that structural in addition to parametric modifications to CAM5's parameterization suite are needed in order to simultaneously well simulate the MJO and mean-state climate.

Beschreibung: During the night of 22-23 October 2012, together with the Hydrology cycle in the Mediterranean eXperiment (HyMeX) Special Observation Period 1 (SOP1) campaign, optical observations of sprite events were performed above a leading stratiform Mesoscale Convective System (MCS) in southeastern France. The total lightning activity of the storm was monitored in three dimensions with the HyMeX Lightning Mapping Array (HyLMA). Broadband Extremely Low Frequency (ELF)/Very Low Frequency (VLF) records and radar observations allowed characterizing the flashes and the regions of the cloud where they propagated. Twelve sprite events occurred over the stratiform region, during the last third of the lightning activity period, and well after the coldest satellite-based cloud top temperature (-62°C) and the maximum total lightning flash rate (11 min -1 ). The Sprite-Producing positive Cloud-to-Ground (SP+CG) strokes exhibit peak current from 14 to 247 kA, Charge Moment Changes (CMC) from 625 to 3086 C km, and Impulsive CMC (iCMC) between 242 and 1525 C km. The +CG flashes that do not trigger sprites are initiated outside the main convective core, have much lower CMC values, and in average, shorter durations, lower peak currents, and shorter distances of propagation. The CMC appears to be the best sprite predictor. The delay between the parent stroke and the sprite allows classifying the events as short-delayed (〈 20 ms) and long-delayed (〉 20 ms). All long-delayed sprites, i.e., most of the time carrot sprites, are produced by SP+CG strokes with low iCMC values. All SP+CG flashes initiate close to the convective core and generate leaders in opposite directions. Negative leaders finally propagate towards lower altitudes, within the stratiform region that coincides with the projected location of the sprite elements.

Beschreibung: Comparisons of collocated Atmospheric Infrared Sounder (AIRS) and Moderate Resolution Imaging Spectroradiometer (MODIS) ice cloud optical thickness (τ) and effective radius (r e ) retrievals and their uncertainty estimates are described at the pixel-scale. While an estimated 27% of all AIRS fields of view contain ice cloud, only 7% contain spatially uniform ice according to the MODIS 1-km optical properties phase mask. The ice cloud comparisons are partitioned by horizontal variability in cloud amount, cloud-top thermodynamic phase, vertical layering of clouds, and other parameters. The magnitudes of τ and r e and their relative uncertainties are compared for a wide variety of pixel-scale cloud complexity. The correlations of τ and r e between the two instruments are strong functions of horizontal cloud heterogeneity and vertical cloud structure, with the highest correlations found in single-layer, horizontally homogeneous clouds over the low-latitude tropical oceans. While the τ comparisons are essentially unbiased for homogeneous ice cloud with variability that depends on scene complexity, a bias of 5–10μm remains in r e within the most homogeneous scenes identified, consistent with known radiative transfer differences in the visible and infrared bands. The AIRS and MODIS uncertainty estimates reflect the wide variety of cloud complexity, with greater magnitudes in scenes with larger horizontal variability. The AIRS averaging kernels suggest scene-dependent information content that is consistent with infrared sensitivity to ice clouds. The AIRS normalized-χ 2 radiance fits suggest that accounting for horizontal cloud variability is likely to improve the AIRS ice cloud retrievals.

Beschreibung: A ground-based aerosol optical depth (AOD) climatology is presented for Cape Point station (CPT), South Africa for the 2008 – 2013 period. CPT is part of the Global Atmosphere Watch Precision Filter Radiometer (GAW-PFR) network which conducts long-term AOD measurements at remote background sites. AOD ( λ = 500 nm) and Ångström exponent (368 to 862 nm; α 368–862 ) averages for the entire period were 0.059 and 0.68, displaying only a weak seasonality. Based on an established method for airmass classification using the in-situ wind direction and 222 Rn concentration, the following four airmass types were used to further investigate AOD: background marine, marine, mixed and continental. AOD was similar for all types but α 368–862 was distinctly lower (0.43) for background marine and higher (1.07) for continental airmasses illustrating the presence of coarse mode and anthropogenic aerosols, respectively. Trajectory cluster analysis of 5-day back-trajectories confirmed/augmented this classification. AOD for background marine and marine airmass types were consistent with ship-based (MAN network) and island (AERONET network) measurements suggesting that CPT is a suitable site to monitor pristine conditions in the South Atlantic and Southern Oceans when 222 Rn concentrations are 〈 100 mBq m −3 .