Radar, Passive Microwave, and Lightning Characteristics of Precipitating Systems in the Tropics

Abstract

The bulk radar reflectivity structures, 85-and 37-GHz brightness temperatures, and lightning characteristics of precipitating systems in tropical Africa, South America, the east Pacific, and west Pacific are documented using data from the Tropical Rainfall Measuring Mission (TRMM) satellite during August, September, and October of 1998. The particular focus is on precipitation features [defined as a contiguous area Ն75 km 2 with either a near-surface reflectivity Ն20 dBZ or an 85-GHz polarization-corrected temperature (PCT) Յ 250 K] with appreciable rainfall, which account for the bulk of the total rainfall and lightning flash density in their respective regions. Systems over the tropical continents typically have greater magnitudes of reflectivity extending to higher altitudes than tropical oceanic systems. This is consistent with the observation of stronger ice scattering signatures (lower 85-and 37-GHz PCT) in the systems over land. However, when normalized by reflectivity heights, tropical continental features consistently have higher 85-GHz PCT than tropical oceanic features. It is inferred that greater supercooled water contents aloft in the tropical continental systems contribute to this brightness temperature difference.Lightning (as detected by the Lightning Imaging Sensor) is much more likely in tropical continental features than tropical oceanic features with similar brightness temperatures or similar reflectivity heights. Vertical profiles of radar reflectivity add additional information to the nonunique lightning-brightness temperature relationships showing that features with lightning tend to have greater magnitudes of reflectivity and smaller decreases of reflectivity with height above the freezing level than systems without detected lightning.Regional comparisons of the lightning, radar, and microwave signatures of precipitating features show that, over the oceans, the west Pacific has the highest frequency of intense precipitation features (by minimum PCT or maximum reflectivity height). Over land, the intense precipitation features occur more frequently in Africa. These observations are consistent with the relative differences in lightning flash density between the land and ocean regions. The quantitative database of land and ocean features presented here provides a substantial observational framework against which cloud and radiative transfer model results can be tested.

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?…”

Regional comparison of West African convective characteristics: a TRMM‐based climatology

“…Satellite-based studies of convective characteristics in various meteorological regimes have been used to look at the broad-scale aspects of convection and their coupling to largescale forcing (Petersen and Rutledge, 2001;Toracinta et al, 2002;Fink and Reiner, 2003;Nesbitt and Zipser, 2003;Petersen and Boccippio, 2004;Xu et al, 2009;Leppert and Petersen, 2010). Additionally, regional characteristics have also been compared (Nesbitt et al, 2000;Geerts and Dejene, 2005;Schumacher and Houze, 2006;Zipser et al, 2006;Fuentes et al, 2008;Liu et al, 2008;Nicholls and Mohr, 2010).…”

Land‐ocean contrasts in lightning activity over the Indian region

“…Though it is clear from these studies that large percentage of lightning activity occurs over land (Turman and Edgar, 1982;Orville and Henderson;Christian et al, 1999), a considerable amount of lightning activity still occurs over oceans and coastal areas. (Hidayat and Ishii, 1998;Boccippio and Goodman, 2000;Ushio et al, 2001;Fullekrug et al, 2002;Toracinta et al, 2002;Williams and Stanfil, 2002;Seity et al, 2003;Altaratz et al, 2003;Williams and Satori 2004;Williams and Chan, 2004;Collier et al, 2006;Pinto et al, 2007;Chronis et al, 2008). There are maritime regions such as Gulf Stream in the Atlantic and in the South Pacific Ocean near Australia, where lightning activity appears frequently.…”