Yu, H., Kaufman, Y., Chin, M., Zhou, M., Tan, Q., Tan, Q., Dickinson, R., and Remer, L., (2004). A Synergy Analysis of Global Aerosols and Assessment of Direct Radiative Effect. Eos Trans. AGU, 85(47), Fall Meet. Suppl. 2004, Abstract # A21E-04
Aerosol-cloud-radiation interactions constitute the largest uncertainty in quantifying the anthropogenic impact on the earth's energy budget and climate. To reduce these uncertainties, an integration of satellite remote sensing, numerical modeling, and ground-based measurement is desired, because individual methods have both advantages and limitations and are complementary to each other. Recent satellite sensors such as MODIS and MISR provide an unprecedented opportunity of characterizing aerosol optical depths on nearly global scale. These sensors also measure the spectral variation and anisotropy of land surface reflection, which are required for assessing the aerosol direct effect. On the other hand, current satellite sensors can not adequately characterize the whole complexity of global aerosol system. As such a synergy of satellite retrievals and model simulations such as GOCART would enhance the capability of satellite remote sensing. The synergy should be evaluated and constrained with ground-truth data from AERONET measurements. In this study we examine the variability of aerosol optical depth from MODIS and MISR retrievals and GOCART simulations using statistical analysis tools, and compare them with AERONET measurements to obtain error parameters. An optimal interpolation analysis is then performed to merge MODIS and MISR retrievals with GOCART simulations to maximize the utility of aerosol products. This integration derives an annual cycle of global aerosol optical depth that has higher correlation and lower bias and matches better with AERONET measurements. The annual average optical depth in 60S-60N is 0.162~0.167 for MODIS and GOCART integration, 0.148~0.169 for MISR and GOCART integration, and 0.151~0.157 for MODIS (over ocean), MISR (over land) and GOCART integration, depending on error parameters. The aerosol direct effect is also assessed using the so-generated aerosol optical depth in conjunction with GOCART simulations of single-scattering albedo and asymmetry factor and the MODIS-retrieved surface albedo. On global average and under clear sky, the aerosol cooling at the surface is about a factor of 2 more than that at the top-of-atmosphere.
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