Retrieval of Effective Diameter Variations in Tropical Cumulonimbus

It is of considerable importance to understand the impacts (if any) of aerosols and other atmospheric constituents on clouds. These impacts may include modification of the optical properties, coverage, dynamical behavior, and/or hydrological role of clouds. The most basic variables that must be measured in order to make progress are cloud coverage, optical thicknesses, and size distributions of the cloud hydrometeors. The recent launch of MODIS (Moderate Resolution Imaging Spectroradiometer) on board NASA’s polar orbiting EOS (Earth Observing System) satellites promises significant advances in observation of the size distribution, using several near-infrared wavelengths. Daytime near-IR reflectivity is particularly helpful since it is quite sensitive to ice particle size (see Liou (1992) for further information). Models are required to relate backscattered intensities to cloud properties, due to dependence of intensity on viewing geometry and cloud optical depth . Uncertainties in these models include assumptions about crystal shape, parameterization of the scattering phase function, and other approximations. They are difficult to test rigorously against observations. Here, we present an analysis of a long record of AVHRR (Advanced High Resolution Radiometer) 3.7 m reflectivity off of cumulonimbus clouds (Cb) that can be used to do this.