Radiative and Hydrological Atmosphere-Surface Interactions

and Their Role in Climate Change 

Our climate system is driven by solar radiation. Much of the solar radiation passes through the atmosphere and is absorbed at the land and ocean surfaces. However, much of the return of this energy to space through thermal radiation is from atmosphere. Hence, a large fraction of the absorbed solar energy is transferred from surface to atmosphere via hydrological cycle. Our group studies how anthropogenic activities, such as land use/cover change, fossil fuel burning and biomass burning, modify the local, regional and global climate through their interactions with radiative and hydrological processes.

 Due to the temporal and spatial heterogeneity of aerosols, and lack of sufficient in-situ measurements, we integrated the MODIS retrievals, GOCART global model simulation, and AERONET/AVHRR retrievals by using assimilation approaches to derive an annual cycle of global distribution of aerosol optical depth at 550nm, and evaluated the aerosol direct radiative forcing at the top of the atmosphere (TOA) with associated land surface anisotropic reflection characteristics from MODIS data. The inclusion of this surface reflection feature is necessary to better characterize the diurnal variation of aerosol forcing, because aerosols change the fraction of direct bream and visible radiation (detail). We also calculated the aerosol direct radiative effects (ADRE) and its normalized form (NADRE) at 550nm for cloud-free and cloudy conditions and for all-mode and fine-mode aerosols. The results suggested that aerosol properties (i.e., single scattering albedo) and surface properties (i.e., albdeo) are the two important factors in determining the direct forcing (Zhou et al., JGR, 2005).

     On regional scales, using an interactively climate-chemistry-aerosol regional climate model, our group investigated various effects of anthropogenic aerosols (sulfate and carbonaceous aerosols) over East Asia. The model simulation demonstrates how aerosols affect the climate via the interaction with clouds. Through the modification of cloud cover and cloud liquid water content, aerosols can provide surface long wave forcing, and hence decrease the diurnal temperature range; Aerosols can also significantly decrease the precipitation and affect the soil moisture and evaporation (detail).