Tuesday, 22 January 2008: 3:30 PM
The evolution of total lightning and radar characteristics of two mesoscale convective systems over Houston
222 (Ernest N. Morial Convention Center)
Mesoscale convective systems (MCSs) are some of the largest convective systems and produce a wide variety of weather including damaging winds, hail, tornadoes, and flooding. They are also prolific lightning producers and many research studies have focused on their cloud-to-ground (CG) properties in relation to storm structure. In our study, Texas A&M University's (TAMU's) lightning detection and ranging (LDAR) network in Houston, TX is used to examine the evolution of total (intracloud (IC) +CG) lightning in conjunction with the National Lightning Detection Network (NLDN) CG flash data and the Houston (KHGX) Weather Surveillance Radar - 1988 Doppler (WSR-88D) reflectivity data of two MCSs that traversed within the effective range of the LDAR network on 31 October 2005 and 21 April 2006. The lightning characteristics of both MCSs evolved with the intensification (weakening) of their stratiform (convective) regions. As the MCSs mature, the slope (i.e., height vs. line-normal distance) of the VHF source distribution rearward of the convective line evolves from extending horizontally rearward to slanting ~ 50 km rearward and ~6 km downward into the stratiform region near the radar bright band and above the melting level. Also, LDAR stratiform flash rates double and the percentage of stratiform flashes originating in the stratiform region increase from 10 - 20% to 50 - 60% in time. NLDN CG flash rates in the stratiform region increase with time as well, with 73% (45%) of the positive CGs originating from the convective line in the April 2006 (October 2005) MCS. Positive CG flashes originating in the stratiform region generally have larger peak currents than those originating from the convective line and then propagate into the stratiform region before reaching the ground. Mean flash heights in the stratiform region also decrease as the stratiform region develops, which could be favorable for sprite production as the MCSs mature. Charge advection and, as the mesoscale updraft develops, in-situ (i.e., non-inductive melting and ice-ice collisional) charging likely generate enhanced charge layers and result in increased lightning activity in the stratiform region of both MCSs.