Transient Luminous Events above Two Mesoscale Convective Systems

1. Transient Luminous Events above Two Mesoscale Convective Systems Timothy J. Lang, Steven A. Rutledge, Walt Lyons, Jingbo Li, Steven A. Cummer, and Don MacGorman NH1.3/AS4.14 EGU2010-5606 1. Introduction 3. Lightning and TLEs 4. CMC Results Two warm-season mesoscale convective systems (MCSs) were analyzed with respect to their production of transient luminous events (TLEs), mainly sprites. The 20 June 2007 symmetric MCS produced 282 observed TLEs over a 4-h period. The 9 May 2007 asymmetric MCS produced 25 observed TLEs over a 2-h period. How did MCS structure and lightning characteristics affect TLE production? The 20 June storm’s TLE production was strongly tied to convective intensity, while 9 May TLE production was associated with weakening of convection. The 20 June TLE parent +CGs initiated either in the convective line or in the stratiform region, but in either case the parent flash tapped upper-level charge during its TLE phase (8.2 km MSL or -25 °C on average for TLEs in range of the LMA). The 9 May TLE parent flashes initiated in convection and tapped lower level charge in the stratiform region (6.1 km MSL or -15 °C). We have analyzed total CMC data for 21 TLE parents from 20 June, 20 TLE parents from 9 May, and 9 non-TLE flashes that had high iCMC (300+ C km) from 20 June. How reliable are real-time iCMC estimates? Correlation is good with post-processed iCMC values, with a slight low bias. The real-time iCMC estimates are excellent for identifying TLE storms. However, real-time iCMC estimates are not a good predictor of total CMC, which is dominated by the continuing current. The 20 June TLE parents had an advantage over 9 May for increasing CMC, since they tapped charge at higher altitude. However, this advantage was countered by 9 May parents neutralizing larger charge amounts via CC. Variable 20 June 9 May Significance No. of TLE parents 21 20 N/A Impulse CMC (C km) 493.2 268.1 >99% Height CMC (km AGL) 7.5 5.7 >99% Impulse Charge (C) 66.1 44.7 97% CC Duration (ms) 56 129 >99% CC Amplitude (kA km) 33.2 13.0 >99% CC Height (km AGL) 7.8 5.7 >99% CC CMC (C km) 1687.7 1558.9 52% CC Charge (C) 221.5 278.3 91% Total CMC (C km) 2180.9 1801.6 84% Height CMC (km AGL) 7.7 5.7 >99% Total Charge (C) 285.3 322.6 76% Rudimentary calculations using estimated flash volume from LMA data suggest that overall volume and density of charge tapped by flashes during their TLE phases was similar among the two storms. But 9 May flashes tapped this charge much more slowly than 20 June. The tortoise vs. the hare! We have very few energetic non-TLE +CGs examined for 20 June, so statistical significance is low. However, non-TLE energetic flashes were very similar to TLE parents, but they had lower CC amplitude leading to reduced total CMC. Overall, results support the hypothesis that TLE-parent +CGs feature high total CMC, leading to upper atmospheric electrical breakdown. Variable 20 June TLE non-TLE Significance No. of flashes 21 9 N/A Impulse CMC (C km) 493.2 501.2 <90% CC Duration (ms) 56 57 <90% CC Amplitude (kA km) 33.2 21.6 <90% CC CMC (C km) 1687.7 1057.7 <90% Total CMC (C km) 2180.9 1558.9 <90% 20 June 2007 9 May 2007 Red dots +CGs, black dots –CGs, triangles TLE parents, circles 100 & 200 km LMA ranges 20 June convective-initiated at high altitude 9 May initiated in S convection Circles = 100 & 200 km Oklahoma LMA Range Stratiform-initiated near melting level Initiated in MCV convection 2. Data Charge Moment Change Sensors (CMC=Q*h; Dash= Range) Optical Cameras to Record TLEs (YRFS) Oklahoma VHF Lightning Mapping Array (LMA; Gray Circles = 100 & 200 km Range) WSR-88D NEXRAD Radar Network (Diamonds) CMC sensors provide real-time measurements of impulse charge moment change (iCMC), and data can be processed to retrieve continuing current (CC) and the total CMC. LMA provides altitude to allow retrieval of total charge. CMC may be key factor in TLE production! TLE parent that discharged forward anvil! Contact Info: Timothy Lang, CSU Atmospheric Science, Ft Collins, CO 80523; (970) 430-5264, tlang@atmos.colostate.edu This work is supported by National Science Foundation grant ATM-0649034 Red dots VHF sources during TLE, black dots other sources, triangles TLE parents, diamonds flash origins Black = 20 June VHF altitudes during TLE (ZTLE), gray = 9 May