Mesoscale Convective Systems Defined by Their 85-GHz Ice Scattering Signature: Size and Intensity Comparison over Tropical Oceans and Continents

Abstract

This study used the 85-GHz ice scattering signature to describe the size, intensity, and geographic distribution of mesoscale convective systems (MCSs) between 35°N and 35°S for January, April, July, and October 1993. An MCS was defined as an area below 250 K of at least 2000 km2, with an enclosed minimum brightness temperature below 225 K. The geographic distribution of MCSs identified by these criteria was consistent with large-scale seasonal dynamics. There was no significant relationship (R2 ≈ 0.05) between the size and intensity for the MCSs in the study database. Tropical South America, tropical Africa, and the oceanic warm pool had the greatest number of MCSs. Equatorial regions such as tropical Africa had the smallest median areas. The subtropical oceans had the largest median areas, about 20% greater than other regions. MCSs in the continental regions tended to have colder minimum brightness temperatures than MCSs in the oceanic regions. The sub-tropical oceans had the warmest median minimum brightness temperatures, and tropical Africa had the coldest. Sunrise/sunset stratification of the data provided additional insight into land?water differences. MCSs were 35% more frequent over the oceans at sunrise than at sunset and 60% more frequent over tropical continents at sunset than at sunrise. Except over the subtropical oceans, MCSs tended to be larger at sunrise than at sunset. Continental MCSs tended to be colder at sunset than sunrise and colder than oceanic MCSs, particularly at sunset. The minimum brightness temperatures of oceanic MCSs tended to be only marginally colder at sunrise than at sunset. In general, continental MCSs appeared to be smaller and more intense than oceanic MCSs, and the largest and the most intense MCSs occurred more frequently in the subtropics.