Cloud-Radiative Feedbacks on Tropical and Midlatitude Storms
Analysis of a combination of almost a dozen satellite-based data products allows for a quantitative determination of all the atmospheric diabatic heating processes. These products are used in a general analysis of the energetics of the atmospheric circulation, which highlights the role played by storm systems. To elucidate the cloud effects on storms further, the cloud product produced by the International Satellite Cloud Climatology Project (ISCCP) is used to identify a small number of "weather states" of the atmosphere, which are then used to separate the radiative heating (and the full diabatic heating) so as to describe the variations as transitions among these states. This analysis approach is used to examine how cloud radiative effects alter the energetics of tropical and midlatitude storms.
Decadal Changes in Surface Radiative Fluxes
Recent evidence suggests that radiative fluxes incident at the Earth surface are not stable over time but undergo significant changes on decadal timescales. This is not only found in the thermal spectral range, where an increase in the downwelling flux is expected with the increasing greenhouse effect, but also in the solar range. Observations suggest that surface solar radiation, after decades of decline ("global dimming"), reversed into a "brightening" since the mid-1980s at widespread locations. This presentation gives an update on recent investigations related to the decadal variations in these fluxes, based on both observational and modeling approaches. Updated observational data, archived at the Global Energy Balance Archive (GEBA) at ETH Zurich, suggest a continuation of surface solar brightening beyond the year 2000 at numerous locations, yet less pronounced and coherent than during the 1990s, with more regions with no clear changes or declines. Current global climate models as used in the IPCC-AR4 report typically do not reproduce the observed decadal variations to their full extent. Modeling attempts to improve this situation are under way at ETH, based on a global climate model which includes a sophisticated interactive treatment of aerosol and cloud microphysics (ECHAM5-HAM). Further the impact of the decadal changes in surface radiative forcings on different aspects of the global climate system and climate change is discussed, such as 20th century day- and nighttime warming, evapotranspiration changes and the varying intensity of the hydrological cycle as well as the terrestrial carbon cycle. Selected related references: Wild, M., and Co-authors, 2005: From dimming to brightening: Decadal changes in solar radiation at the Earth's surface. Science, 308, 847-850 Wild, M., 2007: Decadal changes in surface radiative fluxes and their importance in the context of global climate change, in: Climate Variability and Extremes during the Past 100 years, Advances in Global Change Research, 140, Editors Stefan Brönnimann et al., p. 155-168. Wild, M., Ohmura A., Makowski, K., 2007: Impact of global dimming and brightening on global warming. Geophys. Res. Lett., 34, L04702, doi:10.1029/2006GL028031. Wild, M., Grieser, J. and Schär, C., 2008: Combined surface solar brightening and greenhouse effect support recent intensification of the global land-based hydrological cycle. Geophys. Res. Lett., 35, L17706, doi:10.1029/2008GL034842 Wild, M., 2009: How well do IPCC-AR4/CMIP3 climate models simulate global dimming/brightening and 20th century day- and night-time warming? To appear in J. Geophys. Res. Wild, M., Truessel, B., Ohmura, A., Long, C.N. König-Langlo G., Dutton, E.G., and Tsvetkov, A., 2009: Global Dimming and Brightening: an update beyond 2000. To appear in J. Geophys. Res. Wild, M., 2009: Global dimming and brightening: A review on decadal changes in surface solar radiation. To appear in J. Geophys. Res.
Recent Advances in Earth Radiation Budget Observation
The degree to which anthropogenic forcings (e.g., due to greenhouse gases and aerosols) influence global surface temperature change is highly uncertain owing to differences in the way state-of-the-art global climate models represent the cloud response to global warming. The cloud feedback problem has been recognized for several decades, yet very little progress has been made during this period. This presentation discusses the increasing role that observational records capable of detecting changes in the Earth's radiation budget and cloud properties over decadal time scales can play in reducing cloud feedback uncertainty. Recent advances and results in Earth Radiation Budget observation from the Clouds and the Earth's Radiant Energy System (CERES) program are presented along with climate model results that illustrate how long-term records of ERB observations can be used to reduce cloud feedback uncertainty.
Investigate the Surface Albedo Effect on Terra SSF Edition 2B data by Using the Tropical/Sub-Tropical BSRN Observations
Dong et al.  studied the atmospheric column absorption of solar radiation in the optically thick DCS using collocated surface-satellite observations over tropical and middle latitudes. They also compared the observations with the radiative transfer model calculations and did an error analysis during the comparison. There are two major random errors unsolved in the Dong et al. study, they are ADM errors in Rtoa and time/space matching errors in Asfc. In this study, we collected 12 BSRN stations data over tropical/sub-tropical region (30S -30N), and most of the TERRA overpass (SSF Edition 2B products) during the daytime over the sites. These stations will cover six different surface types, such as water, grass, rock, desert, concrete and shrub. We are going to compare the satellite retrieved downwelling radiation to the BSRN measured solar flux with each SSF FOV under the clear, partial cloud, and overcast condition, investigate the surface albedo variations in each SSF FOV under the clear sky condition, and exam the difference among these different sky conditions and the different surface types over all the available BSRN sites in the tropical/sub-tropical region. The goals of this study are to answer the following question, the uncertainties of the TOA solar fluxes in each SSF FOV caused by the surface types; and/or eliminate the effect of aerosol absorption on the retrieved the downwelling radiation at the surface.
On the Relationship Between Diurnal Temperature Range and Surface Solar Radiation in Europe
The surface solar radiation (SSR) is an important factor influencing the local and global energy budget.
However, information on the spatial and temporal variation of SSR is limited. A more commonly available
measure, which may provide such information, is the diurnal temperature range (DTR). In this study we analyze
the relationship between DTR and SSR in Europe between 1970 and 2005 on seasonal and decadal scale.
When comparing the mean anomalies time series composed of 31 pairs of sites with long-term SSR and DTR
measurements we found a correlation coefficient of 0.87 in the annual mean and between 0.61 and 0.92 in the
seasonal mean anomalies. When investigating the individual pairs of SSR and DTR individually we found that
local correlations are mostly lower than the European mean and that they decrease rapidly in seasons and
latitudes with low incident angles and at high alpine altitude. The highest correlation on local and seasonal
scales seems to be connected with the variability of the large scale circulation in Europe. The output of 11
simulations of current generation regional climate models over Europe confirms the strong relationship
between SSR and DTR. The seasonal dependence of the relationship is well reproduced but the absolute
values of DTR and SSR are mostly too low. The pattern of decrease (dimming) and increase (brightening) in
SSR and DTR was not reproduced in the modeled time series. There is still strong evidence from both models
and observations that DTR is a reliable representative of SSR.
Determining Radiative Heating profiles from Satellite Data Through Classification and Clustering
Knowledge of the vertical structure of radiative heating rates is important to understand distribution of energy within the atmosphere. Currently, detailed information on vertical radiative heating profiles can be derived only from instruments which profile the cloud properties in the atmosphere (i.e, radar and lidar). Vertical profiles of cloud properties and radiative heating rates have been derived at high temporal resolution from measurements at the Atmospheric Radiation Measurement (ARM) program sites. However these measurements typically represent horizontal scales much smaller than those represented in climate models, making it difficult to compare the two sets of cloud and radiation fields. By combining the ARM surface measurements with geostationary satellite measurements, the detailed knowledge of vertical structure gained from the ARM measurements can be expanded to a larger horizontal scale, giving a better understanding of the full atmospheric radiation budget. In previous work, we have defined 'classes' of radiative heating rate profiles and shown that there are typical cloud and heating rate structures that are observed at multiple tropical sites. In this study we expand on the previous work to explore the possibility of classifying geostationary satellite data into a given heating rate profile class. Such classification is the first step in creating a 3D heating rate product.