Estimation of Precipitation Area and Rain Intensity Based on the Microphysical Properties Retrieved from NOAA AVHRR Data

摘要

This paper investigates the feasibility of a quantitative estimation of precipitation from space, based on retrieval of microphysical properties of cloud tops using Advanced Very High Resolution Radiometer data. The effective radius r_e of cloud particles is calculated for highly reflective clouds in the visible wavelength, assuming that these are water clouds with infinite optical thickness at the 3.7-mum channel. A large effective radius indicates the presence of large droplets and/or ice in the clouds. The distinction between large droplets and ice is not necessary because the existence of either near the tops of thick clouds is conducive to the precipitation formation processes. In addition to the microphysical information, the fraction of raincloud coverage and cloud spatial structure (convective and stratiform) were used for the rain estimation algorithm. The satellite estimates were compared to radar data. Encouraging results were obtained for winter precipitation clouds in Israel with a wide range of cloud-top temperatures. The method is not limited by temperature thresholds, resulting in estimates for rain intensity of clouds that do not necessarily contain large amounts of ice. Reasonable rain intensity estimates for clouds with relatively warm tops have not yet been obtained by other passive radiation methods, especially over land.