Beate Liepert (PI)
Lamont-Doherty Earth Observatory
liepert@ldeo.columbia.edu

Interannual Variability of Surface Radiation Budget and Climate Feedback

The proposed study investigates the interannual variability of surface radiative fluxes, the possible causes of the variability and the impacts on the climate system. The investigations of cloud feedback mechanisms in combination with the general circulation are of particular interest. Hence the goal of this study lies within the scope of the NASA's Earth System Enterprise NRA namely the investigation of changes in the Earth's radiation and climate. Recent studies show an unexpectedly high variability of surface solar radiation (''dimming'') of about 7 watts per square meter in the last decades with a recent recovery back to mid last century values in some regions. Cloud coverage decreases have also been reported for the 1990s. It is suspected that part of this variability in the shortwave irradiance is due to the influence of aerosol effects from anthropogenic sources, and from major volcanic eruptions. Furthermore, cloud feedbacks and global warming with its feedbacks modify both shortwave and longwave surface radiative fluxes. The surface solar radiation is highly sensitive to aerosol forcing because the surface fluxes are reduced by scattered and by absorbed solar energy. The latter one cannot be seen from the top of the atmosphere. Since radiative fluxes at the surface are balanced by non-radiative fluxes, small changes lead to direct changes in latent heat and sensible heat fluxes that modify convection and evaporation. The proposed analysis of surface radiative fluxes in climate models and observations is therefore a crucial component in assessing the impact of aerosols and greenhouse gas forcing on the hydrological cycle. We plan to focus our investigation on the time period of satellite observations from 1983 to present. Surface radiation data and cloud information from ISCCP-FD will be analyzed together with in situ measurements from Baseline Surface Radiation Network BSRN stations for various climatic conditions (e.g. El Nino and monsoon system). Surface radiative and non-radiative fluxes of GISS-GCM experiments with varying forcings will be analyzed. Additional model experiments with the GISS modelE will be designed and performed to test hypothesis for explaining possible changes in surface radiation and cloud feedbacks. The proposed project aims to improve our prediction ability of future climate change by explaining observed interannual variability of surface radiation with climate simulations and observational data analysis.

+ Back to Participant Listing