CLASSIFICATION OF CLOUDS OVER THE WESTERN EQUATORIAL PACIFIC-OCEAN USING COMBINED INFRARED AND MICROWAVE SATELLITE DATA

A new cloud classification scheme is presented that combines infrared and microwave satellite data. Because microwave radiation can penetrat e deep into the cloud layer, this scheme is able to determine characte ristics for both thin and deep clouds. Additionally, the new scheme ca n provide information on precipitation, which traditional infrared-vis ible cloud classification schemes have been unable to. The proposed cl oud classification scheme utilizes the cloud top temperature obtained from infrared measurements and a microwave index that includes both em ission and scattering signals. The following eight cloud classes are d efined: warm nonprecipitating cloud, warm precipitating cloud, midtop nonprecipitating cloud, midtop precipitating cloud, thin high-top nonp recipitating cloud, deep high-top nonprecipitating cloud, anvil with s tratiform precipitating cloud, and deep convective precipitating cloud . The classification scheme is validated by aircraft radar data obtain ed from Tropical Ocean-Global Atmosphere Coupled Ocean-Atmosphere Resp onse Experiment. The new cloud classification scheme is used to invest igate the clouds in the western equatorial Pacific Ocean warm pool reg ion for the period from November 1992 to February 1993, allowing us to obtain for the first time the spectra of cloud coverage and precipita tion distribution as a function of cloud types. The analysis shows tha t most of the cloudiness in this region is associated with warm nonpre cipitating clouds. Precipitating pixels comprise only about 15% of tot al cloud pixels. Of the precipitating pixels, about 50% have cloud top temperatures warmer than -40 degrees C. Using rainfall rates obtained from microwave satellite data, the relative contribution by each prec ipitating cloud type is investigated. It is found that the precipitati ng clouds with cloud top temperature warmer than -40 degrees C contrib ute at least 23% of the total rainfall amount, while the remaining 77% of total precipitation is divided. almost equally by anvil with strat iform precipitating cloud and the deep convective precipitating cloud.