Evolution of charge and lightning throughout an observed and simulated supercell storm.

摘要

A high-precipitation tornadic supercell storm was observed by multiple platforms on 29 May 2004 during the Thunderstorm Electrification and Lightning Experiment (TELEX). Observational systems included the Oklahoma Lightning Mapping Array (LMA), mobile balloon-borne soundings, and two mobile SMART-R (SR) C-Band radars. This dissertation utilizes data from these platforms to relate the spatial distribution and evolution of lightning to storm kinematics and microphysics, especially to regions of microphysical charging and the location and geometry of those charge regions. One example is the relationship of the observed transient lightning hole and of large lightning densities to kinematic properties inferred from dual-Doppler analyses of the SR data.;The lightning flashes near the core of this storm, although extraordinarily frequent, tended to have shorter duration and smaller horizontal extent than typical flashes in other storms having less frequent lightning. This is due, at least in part, to many small pockets of charge lying in close proximity to small pockets of the opposite polarity of charge. Thus, each polarity of lightning leader propagates only a relatively short distance before reaching regions of unfavorable electrical potential. In the anvil, however, lightning extended tens of kilometers from the reflectivity cores in roughly horizontal layers, consistent with the charge spreading through the anvil in broad sheets.;Previous studies of lightning in anvil clouds have reported that flashes began in or near the storm core and propagated downwind into the anvil, and many flashes followed that pattern in this storm. However, this dissertation presents the first observations of flashes that began in the anvil 30-100 km from the cores of the storms and propagated upwind back toward the cores. It had been thought that flashes could not be initiated far downwind in the anvil, because anvil charge was thought to be produced mainly in the storm's deep updraft and to decrease with distance into the anvil. Interaction between charge regions in the two converging anvils of adjoining storms appeared to cause some of the distant flash initiations, but a local charging mechanism in the anvil likely also contributed to the flash initiations.;The observations cited above are compared with results from simulations using the Collaborative Model for Multiscale Atmospheric Simulation (COMMAS) with two-moment microphysics, seven hydrometeor categories, and parameterizations for electrification and lightning and employing an ensemble Kalman filter for mobile radar data assimilation. The simulated precipitation and wind fields were similar to those of the observed storm. Simulated lightning flash rates were very large, as was observed, and the distribution of charge in the main body of the storm revealed in the simulation details the lightning dependence on storm kinematics that could not be directly observed. The simulation produced observed lightning holes and the high-altitude lightning seen in the observations. However, the simulation failed to produce the observed lightning initiations (or even lightning channels) in the distant downstream anvil; instead, the simulated lightning was confined to the main body of the storm.