Evolution of radar reflectivity and total lightning characteristics of the 21 April 2006 mesoscale convective system over Texas

Abstract

On 21 April 2006 a mesoscale convective system (MCS) passed within range of the Houston (KHGX) operational Weather Surveillance Radar — 1988 Doppler (WSR-88D, S-band) and the Houston Lightning Detection and Ranging (LDAR) network, which measures the time and three-dimensional location of total, or both intracloud (IC) and cloud-to-ground (CG), lightning. This study documents the evolution of total lightning and radar reflectivity for the 21 April 2006 MCS over Texas, with emphasis on the stratiform region and those processes in the convection region that likely influence stratiform region development. As the MCS traverses the LDAR network, the system slowly matures with a weakening convective line and a developing stratiform region and radar bright band. The area of stratiform precipitation increases by an order of magnitude and mean stratiform radar reflectivity increases by 7–8 dB in the radar bright band and mixed-phase zone (0° to − 10 °C) just above it. As the stratiform region matures, the total lightning pathway slopes rearward and downward from the back of the convective line and into the stratiform region. At early times, the pathway extends horizontally rearward 40 to 50 km into the stratiform region at an altitude of 10 to 12 km. Near the end of the analysis time period, the total lightning pathway slopes rearward 40 km and downward 6 km through the transition zone before extending 40 to 50 km in the stratiform region at an altitude of 5 to 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 region total lightning flash rate increases and total lightning heights decrease. The percentage of stratiform total lightning flashes originating in the stratiform region increases significantly from 10% to 45%. The number of positive CG flashes in the stratiform region also increases with 73% originating 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 total lightning production of the stratiform region.