A Comparison of WSR-88D Reflectivities, SSM/I Brightness Temperatures, and Lightning for Mesoseale Convective Systems in Texas. Part II. SSM/I Brightness Temperatures and Lightning

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  • a Department of Meteorology, Texas A&M University, College Station, Texas
  • | b Cooperative Institute for Applied Meteorological Studies, Department of Meteorology, Texas A&M University, College Station, Texas
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Abstract

This study examines simultaneous SSM/I and lightning data for a sample of nine mesoscale convective systems (MCS) near League City, Texas. Comparison of lightning files of varying sizes from ±2 to ±30 min revealed that the ±10-min interval representatively sampled electrical activity in mesoscale systems. The data strongly suggested that flash density was inversely correlated with 85-GHz brightness temperature. The highest negative flash densities corresponded to low (<200 K) brightness temperatures. This relationship can be attributed to the scattering of upwelling 85-GHz radiation by graupel and hail, the same large particles believed to be necessary for charge separation. Variations were found depending on the sizes of an MCSs convective regions and its stage of development. The majority of positive flashes were located in the 210–250-K range. This brightness temperature range was comparable to the brightness temperature range of trailing stratiform regions and was consistent with observations of a higher percentage of positive lightning in stratiform regions. The results of both parts of this study implied that the pattern and magnitude of brightness temperature depressions and, by extension, the amount and distribution of lightning of an MCS was related to the presence of large ice particles in the mixed-phase region of that MCS.

Abstract

This study examines simultaneous SSM/I and lightning data for a sample of nine mesoscale convective systems (MCS) near League City, Texas. Comparison of lightning files of varying sizes from ±2 to ±30 min revealed that the ±10-min interval representatively sampled electrical activity in mesoscale systems. The data strongly suggested that flash density was inversely correlated with 85-GHz brightness temperature. The highest negative flash densities corresponded to low (<200 K) brightness temperatures. This relationship can be attributed to the scattering of upwelling 85-GHz radiation by graupel and hail, the same large particles believed to be necessary for charge separation. Variations were found depending on the sizes of an MCSs convective regions and its stage of development. The majority of positive flashes were located in the 210–250-K range. This brightness temperature range was comparable to the brightness temperature range of trailing stratiform regions and was consistent with observations of a higher percentage of positive lightning in stratiform regions. The results of both parts of this study implied that the pattern and magnitude of brightness temperature depressions and, by extension, the amount and distribution of lightning of an MCS was related to the presence of large ice particles in the mixed-phase region of that MCS.

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