No abstract

[1] Tropical deep convection with overshooting tops is identified by defining five different reference heights using a 5-year TRMM database. The common properties of these extreme convective systems are examined from a global perspective. It is found that 1.3% of tropical convection systems reach 14 km and 0.1% of them may even penetrate the 380 K potential temperature level. Overshooting convection is more frequent over land than over water, especially over central Africa, Indonesia and South America. The seasonal, diurnal and geodistribution patterns of overshooting deep convection show very little sensitivity to the definition of the reference level. The global distribution of overshooting area, volume and precipitating ice mass shows that central Africa makes a disproportionately large contribution to overshooting convection. A semiannual cycle of total overshooting area, volume and precipitating ice mass is found.

An event-based method of analyzing the measurements from multiple satellite sensors is presented by using observations of the Tropical Rainfall Measuring Mission (TRMM) precipitation radar (PR), Microwave Imager (TMI), Visible and Infrared Scanner (VIRS), and Lightning Imaging System (LIS). First, the observations from PR, VIRS, TMI, and LIS are temporally and spatially collocated. Then the cloud and precipitation features are defined by grouping contiguous pixels using various criteria, including surface rain, cold infrared, or microwave brightness temperature. The characteristics of measurements from different sensors inside these features are summarized. Then, climatological descriptions of many properties of the identified features are generated. This analysis method condenses the original information of pixellevel measurements into the properties of events, which can greatly increase the efficiency of searching and sorting the observed historical events. Using the TRMM cloud and precipitation feature database, the regional variations of rainfall contribution by features with different size, intensity, and PR reflectivity vertical structure are shown. Above the freezing level, land storms tend to have larger 20-dBZ area and reach higher altitude than is the case for oceanic storms, especially those land storms over central Africa. Horizontal size and the maximum reflectivity of oceanic storms decrease with altitude. For land storms, these intensity measures increase with altitude between 2 km and the freezing level and decrease more slowly with altitude above the freezing level than for ocean storms.

Cold cloud features (CCFs) are defined by grouping six full years of Tropical Rainfall Measuring Mission (TRMM) infrared pixels with brightness temperature at 10.8-m wavelength (T B11 ) less than or equal to 210 and 235 K. Then the precipitation radar (PR)-observed precipitation area and reflectivity profiles inside CCFs are summarized and compared with the area and minimum temperature of the CCFs. Comparing the radar with the infrared data, significant regional differences are found, quantified, and used to describe regional differences in selected properties of deep convective systems in the Tropics. Inside 4 million CCFs, 35% (57%) of cold cloud area with T B11 Յ 235 K (210 K) have rain detected by the PR near the surface. Only ϳ1% of the area of T B11 Յ 210 K have 20 dBZ reaching 14 km. CCFs colder than 210 K occur most frequently over the west Pacific Ocean, but 20-dBZ echoes extending above 10 km in this region are disproportionately rare by comparison to many continental regions. Ratios of PR-detected raining area to area of T B11 Յ 235 K are higher over central Africa, Argentina, and India than over tropical oceans. After applying these ratios to the climatological Global Precipitation Index (GPI) tropical rainfall estimates, the regional distribution is more consistent with the rainfall retrieval from the PR. This suggests that the discrepancy between GPI-and PR-retrieved rainfall can be partly explained with the nonraining anvil. Categorization of CCFs based on the minimum T B11 , size of CCFs, and 20-dBZ heights demonstrates that 20-dBZ echoes above 17 km occur most frequently over land, while the coldest clouds occur most frequently over the west Pacific. The vertical distances between the cloud-top heights determined from T B11 and PR 20-dBZ echo-top heights are smaller over land than over ocean and may be considered as another proxy for convective intensity.

[1] Relationships between the vertical profile of radar reflectivity and lightning flash rates are investigated using 13 years of Tropical Rainfall Measuring Mission (TRMM) observations during 1998-2010. First the Radar Precipitation Features (RPFs) are defined by grouping raining areas detected by the TRMM Precipitation Radar (PR). Then the characteristics of radar reflectivity and lightning flash rate are calculated in each RPF using PR and Lightning Imaging Sensor (LIS) observations. Using these RPFs, temperatures at 20, 30, and 40 dBZ radar echo tops, used as proxies of the maximum convective intensity of precipitation systems, are examined as indicators of the probability of lightning. Although 30 and 40 dBZ echo top temperatures are better indicators of the probability of lightning than the 20 dBZ echo top temperature, there is a large regional variation in the temperature thresholds, especially between land and ocean. In general, oceanic thunderstorms have higher 20 dBZ echo top and larger horizontal extent than those over land. However, radar reflectivity is more likely to exceed 30 and 40 dBZ at cold temperatures over land than over ocean. The correlations between flash rates and radar echo top temperatures, areas and volumes of radar reflectivity, and ice water contents in the mixed phase region are analyzed using RPFs with at least one flash. In agreement with previous studies, the correlations with the echo top temperatures are low, but the correlations between flash rates and areas and volumes of high radar reflectivity in the mixed phase region are much higher. There is a high correlation between the flash rates and the volumes with radar reflectivity greater than 30, 35, or 40 dBZ in the mixed phase region, but the correlation coefficient varies significantly between thunderstorms over different regions, especially between land and ocean. These results are confirmed by repeating the analysis for regions of the storms defined as convective, thus eliminating the contribution from large areas of stratiform radar echo that have much less lightning.Citation: Liu, C., D. J. Cecil, E. J. Zipser, K. Kronfeld, and R. Robertson (2012), Relationships between lightning flash rates and radar reflectivity vertical structures in thunderstorms over the tropics and subtropics,