Characteristics of tropical cirrus cloud optical thickness fields using MODIS level-3 data

摘要

Cirrus clouds have been identified as one of the most uncertain components in climate research. They are located at high altitudes (near the tropopause), are frequently optically thin in nature, and are composed of non-spherical ice crystals. In this paper, we detail a method for inferring tropical cirrus cloud optical thickness from MODIS level-3 derived cirrus reflectance and solar/satellite view geometry data. We then demonstrate the applicability of this method using an independent MODIS level-3 data file from NASA s Aqua satellite to obtain the average daily tropical cirrus optical thickness. A preliminary study has also been conducted to ascertain the general characteristics of tropical cirrus cover as a whole using two consecutive years of Aqua MODIS global daily data. This study includes the frequency of occurrence (percentage of days with cirrus cover) and the spatial distribution of optical thickness fields. The retrieval method described here is complimentary to the standard operational MODIS cloud products (included in level-3 data) for the case of tropical cirrus clouds.