HR: 11:20h
AN: AE32A-04    [Abstracts]
TI: Mesoscale Convective Systems Which Do and Do Not Produce Sprites: Results From STEPS 2000
AU: * Lyons, W A
EM: Walt.Lyons@FMA-Research.com
AF: FMA Research, Inc., 46050 Weld County Road 13, Fort Collins, CO 80524 United States
AU: Andersen, L M
EM: Laura_Marie_14@hotmail.com
AF: FMA Research, Inc., 46050 Weld County Road 13, Fort Collins, CO 80524 United States
AU: Nelson, T E
EM: TNelson@frii.com
AF: FMA Research, Inc., 46050 Weld County Road 13, Fort Collins, CO 80524 United States
AU: Cummer, S A
EM: cummer@ee.duke.edu
AF: Duke University, Electrical and Computer Eng., Durham, NC 27708 United States
AU: Jauget, N C
EM: nicolas_jaugey@hotmail.com
AF: Duke University, Electrical and Computer Eng., Durham, NC 27708 United States
AU: Huffines, G R
EM: Gary.Huffines@UNCO.edu
AF: University of Northern Colorado, Physics, Earth Sciences and Chemistry, Greeley, CO 80639 United States
AB: During the Severe Thunderstorm Electrification and Precipitation Study (STEPS) conducted during the summer of 2000 over the High Plains, we addressed two basic questions. First, what are the characteristics of those positive cloud-to-ground strokes (+CGs) which produce transient luminous events (TLEs), especially sprites, halos and elves? It was found the vast majority TLEs optically confirmed over High Plains storms were associated with large charge moment change events (DMq), exceeding thresholds of several hundred C km, substantially larger than the DMq for "normal" lightning. This finding is entirely consistent with present theoretical models of sprite ignition at ~75 km due to conventional breakdown. The second question addressed concerned what types of storms produced these unusual CG discharges. Not all mesoscale convective systems (MCSs) produce TLEs, or if they do, do so only for certain stages in their life cycle. Why? Meteorological analyses of TLE-producing systems had determined that the TLE parent +CGs were concentrated mostly in the stratiform region of their parent storms. Initial and updated analyses for Lightning Mapping Array data from the New Mexico Tech system suggested that the majority of the charge in the parent +CGs was removed from relatively low altitudes in the storm, typically 3 to 5 km AGL. After summarizing the characteristics of over 1500 TLEs and their parent MCSs, some clear criteria have become evident. First the cloud top canopy must be larger than 20,000 sq. km at the 50C level, and the coldest temperature must be at least -55C. Second, the peak reflectivity somewhere in the parent storm must exceed 55 dBZ. This requirement for a very tall and also intense storm initially seems at odds with the known environment of TLE parent CGs (low in the startiform region). Yet, as will be discussed, the emerging conceptual models of TLEs within trailing stratiform regions suggests the overall picture is indeed consistent with what is known about MCS internal structures and circulations. In addition, an observation campaign was conducted during summer 2005. A classic MCS producing spites was monitored using the impulse charge moment change techniques developed by Duke University. A case study for the 2 July 2005 MCS will be used to illustrate the updated sprite/MCS model.
UR: http://www.Sky-Fire.TV
DE: 0342 Middle atmosphere: energy deposition (3334)
DE: 3324 Lightning
DE: 3329 Mesoscale meteorology
DE: 3360 Remote sensing
SC: Atmospheric and Space Electricity [AE]
MN: Fall Meeting 2005