Different optical properties of high cloud in GMS and MODIS observations

The optical properties of high cloud are compared between two satellite retrievals taken from the Geostationary Meteorological Satellite-5 (GMS) and the Moderate-resolution Imaging Spectroradiometer ( MODIS) in the tropical western Pacific (TWP) for the years 1998 - 2001. The MODIS high-cloud amount determined by 1.38-mu m reflectances (> 1.1%) is approximately twice that of GMS determined by 11-mu m brightness temperatures (< 260 K). The optical depths associated with the retrieved high clouds are calculated using a radiative transfer model. The minimum detectable value of optical depths by the MODIS and GMS measurements is around 0.1 and 2.0, respectively. Variations of MODIS and GMS high clouds with respect to the mean sea surface temperatures (SSTs) in the TWP are examined next. There exist large discrepancies in the change rates in high clouds with increasing SST between GMS and MODIS in the available data for the years 2000 and 2001.