Seasonal variation of cloud particle size as derived from AVHRR remote sensing

Abstract

We have analyzed long-term NOAA/AVHRR (Advanced Very High Resolution Radiometer) global data from 1985 to 1994 to investigate the variation of the cloud particle size for low-lying water clouds. Here we focus on seasonal change of the cloud particle size instead of studying the variability the absolute values, since there are several critical factors which affect the long time-series thus obtained, such as calibration uncertainty, sensor degradation, change of satellite platform, orbital shift and so on. Amazon and East Asia cases will be shown in addition to global average. All the cases show decreasing trend with signals of significant seasonal cycles (particularly local cases such as Amazon and East Asia). The interannual decreasing trend and a gap in 1989 would be artifacts caused from above reasons. Seasonal cycles, however, would be explained by the seasonal change in precipitation that is able to control the amount of aerosol and cloud particles, though we need to be careful to propose such a direct relationship between them, since water clouds do not cover all the precipitating clouds.