The Evolution of Total Lightning and Radar Reflectivity Characteristics of Two Mesoscale Convective Systems Over Houston, Texas

The Evolution of Total Lightning and Radar Reflectivity Characteristics of Two Mesoscale Convective Systems Over Houston, Texas
Author: Charles Lee Hodapp
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Release: 2010
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Two mesoscale convective systems (MCSs) passed over the Houston Lightning Detection and Ranging (LDAR) network on 31 October 2005 and 21 April 2006. As the MCSs traverse the LDAR network, the systems slowly mature with a weakening convective line and a developing stratiform region and radar bright band. The intensification of stratiform region precipitation, including the bright band, is thought to play an important role in stratiform lightning structure, charge structure, and total lightning production of MCSs. The stratiform areas quadruple in size and the mean reflectivity values increase substantially by ~ 6 dB. As the stratiform region matures, VHF source density plots show a lightning pathway that slopes rearward and downward from the back of the convective line and into the stratiform region. At early times for both MCSs, the pathway extends horizontally rearward 40 to 50 km into the stratiform region at an altitude of 9 to 12 km. Near the end of the analysis time period, the pathway slopes rearward 40 km and downward through the transition zone before extending 40 to 50 km in the stratiform region at an altitude of 4 - 7 km. The sloping pathway likely results from charged ice particles advected from the convective line by storm relative front-to-rear flow while the level pathway extending further into the stratiform region is likely caused by both charge advection and local in-situ charging. As the stratiform region matures, the stratiform flash rates double and lightning heights decrease. The percentage of lightning flashes originating in the stratiform region increases significantly from 10 - 20% to 50 - 60%. Overall, the number of positive cloud-to-ground flashes in the stratiform region also increases. Between both MCSs, 60% of the positive CGs originated in the convective or transition regions. Both in-situ charging mechanisms created by the development of the mesoscale updraft and charge advection by the front-to-rear flow likely contribute to the increased electrification and lightning in the stratiform region.

Three-Dimensional Radar and Total Lightning Characteristics of Mesoscale Convective Systems

Three-Dimensional Radar and Total Lightning Characteristics of Mesoscale Convective Systems
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Release: 2003
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The radar and electrical characteristics of three linear leading convective/trailing stratiform midlatitude mesoscale convective systems (MCSs) that passed through Dallas-Fort Worth, Texas on the following dates are examined: 1) 7-8 April 2002, 2) 12-13 October 2001, and 3) 16 June 2002. Quantitative results from the April and June MCSs are presented, but data problems with the October MCS restricted partitioned analysis to qualitative results. The convective line produced ~69% and ~93% of the total cloud-to-ground (CG) lightning flashes in the April and June MCSs, respectively. The convective line CG flash rate averaged 12.3 flashes min-1 (53.6 flashes min-1) in the April (June) case study, and only 7.5% (2%) of these flashes were positive in polarity. Lightning Detection and Ranging (LDAR II) source data identified two main electrically-active regions present within the convective line in the following temperature layers: 1) 0 to -25 & deg;C, and 2) -35 to -55 & deg;C. The lower region (1) was most likely a combination of the main negative and the lower positive charge centers of the thunderstorm tripole, and the upper region (2) was most likely the upper positive charge center of this tripole. Convective echo volume aloft (e"30 dBZ, 0 to -40 & deg;C) was strongly correlated to convective lightning activity, suggesting that the presence of strong updrafts and differential sedimentation caused convective line electrification via the non-inductive charging (NIC) mechanism. The stratiform region CG flash rate averaged 2.2 flashes min-1 (4.5 flashes min-1) in the April (June) case study, and ~45% (~27%) of these flashes were positive in polarity. LDAR II source data identified one primary electrically-active layer (at -10 to -25 & deg;C) that was sloped from the upper portions of the convective line rearward to just above the bright band in the stratiform region. A small and spatially distinct secondary electrically-active layer (at ~ -40 & deg;C) was located towards.