Three Years of TRMM Precipitation Features. Part I: Radar, Radiometric, and Lightning Characteristics

Abstract

During its first three years, the Tropical Rainfall Measuring Mission (TRMM) satellite observed nearly six million precipitation features. The population of precipitation features is sorted by lightning flash rate, minimum brightness temperature, maximum radar reflectivity, areal extent, and volumetric rainfall. For each of these characteristics, essentially describing the convective intensity or the size of the features, the population is broken into categories consisting of the top 0.001%, top 0.01%, top 0.1%, top 1%, top 2.4%, and remaining 97.6%. The set of "weakest/smallest" features composes 97.6% of the population because that fraction does not have detected lightning, with a minimum detectable flash rate of 0.7 flashes (fl) min Ϫ1 . The greatest observed flash rate is 1351 fl min Ϫ1 ; the lowest brightness temperatures are 42 K (85 GHz) and 69 K (37 GHz). The largest precipitation feature covers 335 000 km 2 , and the greatest rainfall from an individual precipitation feature exceeds 2 ϫ 10 12 kg h Ϫ1 of water. There is considerable overlap between the greatest storms according to different measures of convective intensity. The largest storms are mostly independent of the most intense storms. The set of storms producing the most rainfall is a convolution of the largest and the most intense storms.This analysis is a composite of the global Tropics and subtropics. Significant variability is known to exist between locations, seasons, and meteorological regimes. Such variability will be examined in Part II. In Part I, only a crude land-ocean separation is made. The known differences in bulk lightning flash rates over land and ocean result from at least two differences in the precipitation feature population: the frequency of occurrence of intense storms and the magnitude of those intense storms that do occur. Even when restricted to storms with the same brightness temperature, same size, or same radar reflectivity aloft, the storms over water are considerably less likely to produce lightning than are comparable storms over land.

On the relationships between lightning frequency and thundercloud parameters of regional precipitation systems

“…[24] Thresholds for lightning occurrence in terms of radar reflectivity or microwave brightness temperature in different parts of the world have been examined by many authors [MacGorman and Rust, 1998;Toracinta et al, 2002;Cecil et al, 2005;Yuan and Qie, 2008]. Their results show that thresholds are land or ocean dependent but very similar in different weather regimes.…”

“…Significant differences exist on thresholds for lightning occurrence between land and oceanic weather systems. For example, even with the same passive microwave brightness temperature or the same vertical profile of radar reflectivity, continental storms are much more likely to produce lightning than oceanic systems [Toracinta et al, 2002;Cecil et al, 2005]. The motivating questions here are: Do differences of thresholds for lightning production exist between different weather regimes in the same location?…”

Morphology of the tropopause layer and lower stratosphere above a tropical cyclone: a case study on cyclone Davina (1999)

“…TRMM measures cloud-top altitude and rainfall characteristics (Cecil et al, 2005), see Sect. 3 hereafter.…”

Distribution of Convective Intensities in West Africa Using Reflectivity and Ice Scattering Characteristics from TRMM Precipitation Features

“…Following [17] which was based on [18] and physical reasoning outlined in many other studies, proxies for convective intensity are defined as follows:  The higher the height attained by the 40-dBZ level in a PF, the more intense the storm;  The lower the minimum brightness temperature attained in a PF at 37 and 85 GHz, the more intense the storm; and  The greater the lightning flash rate attained in a PF, the more intense the storm.…”

“…[16] reasoned that storms containing higher 30 dBZ heights likely contain more intense electric fields (and therefore more lightning), larger supercooled water and ice water contents; the second condition leading to lower 85-GHz PCTs. Following this reasoning and the conditions highlighted in [17] which was based on [18] and physical reasoning outlined in many other studies, we simply classify such land areas or locations as a high storm area especially the pointed domains. This is in conformity with the fact that the presence of AEJ triggers thunderstorms and lightning activities in these areas during this season (MAM)…”