Summer daytime precipitation in ice, mixed and water phase as viewed by PR and VIRS in tropics and subtropics

Abstract

Climatological characteristics of summer daytime precipitation and its signals of visible infrared in ice, mixed and water phase in tropics and subtropics are investigated for through merged VIRS and PR data from 1998 to 2012. Results indicate that the frequency of precipitation in ice phase varies from 1% to 20%, which is at least 2% higher than that in mixed phase over the tropical land and ocean. For precipitation in water phase, the frequency is about 1% uniformly distributed over ocean. In the region of Asian Summer Monsoon, especially in the Bay of Bengal and South China Sea, prosperous precipitation in ice phase is obvious against the higher in mixed phase over East China. The precipitation in the region of ITCZ, especially in the western and eastern Pacific Ocean, is mainly in ice phase, which suggests the stronger convective activities over this region. In the mid-latitude of southern hemisphere, much more mixed-phase precipitation occurs, which should be related to activities of cold front systems. At VIRS channel 0.63 μm and its ratio to channel 1.6 μm, significant differences appear among the three phases, which suggests a simple threshold method to classify precipitation in the three phases by using the ratio. Over ocean, the mean height of rain top detected by PR shows 7.0 km, 5.5 km and 3.0 km for precipitation in phases of ice, mixed and water, respectively, which is at least 0.5 km lower than those over land. Over the Tibet Plateau, the mean rain top can reach over 7.5 km for precipitation in the three phases. Studies indicate that large mean rain rate, over 4.5 mm/h, is represented by precipitation in ice phase comparing with that in the other two phases. The vertical structures in the contoured frequency by altitude diagram (CFAD) also reveal big differences among precipitation in the three phases over land and ocean. However, statistics for relationship between near surface rain rate and signals at each VIRS channels show that the ratio of reflectivity at 0.63 μm to 1.65 μm may be a good approach to retrieve rain rate for precipitation in different phases.