2.3
The Morphology of Supercell Storms on 2 June 1995: Intriguing Observations of Cloud-to-Ground Lightning Properties and Interactions with Pre-existing Mesoscale Boundaries
Matthew S. Gilmore, Texas A&M University, College Station, TX
Radar (KLBB WSR 88-D) and cloud-to-ground lightning characteristics of 14 supercells are analyzed between 3 and 9 PM (CST) on 2 June 1995. These supercells meet the following objective criteria output by the NSSL Mesocyclone and Hail Detection Algorithms at some time in the storm evolution: mesocyclone rank greater than 5 and maximum expected hail size (MEHS) greater than 2.54 cm. Highly interactive storms are rejected from analysis. Applying these criteria results in 14 cells for the radar/lightning analysis. Also analyzed for these cells are VIL, 40dBZ echo top (proxy for updraft strength), storm track, and echo area orientation and behavior. Results from this analysis are also used as a basis for comparison to numerical supercell simulations.
Three main results are found in this study that are consistent with other recent studies. The first is that storms dominated by -CG flashes are separated in geographic extent from the +CG dominated storms. The second is the tendency for +CG dominated storms to switch to -CG dominated; usually during supercell "spinup" or storm splitting. The third is the tendency for +CG dominated storms to form or intensify rapidly as well as being more likely to be associated with tornadoes.
Those supercells producing damage-intensity F1 or greater tornadoes also produce a large fraction of +CG lightning and do so after crossing a pre-existing mesoscale outflow boundary. Storms that increase in percent positive flashes after crossing the boundary also increase in updraft strength and rotation. Larger hail is reported with storms on the cool side of the boundary than on the warm side. While large hail is not exclusive to the +CG dominated storms, large numbers of +CG flashes tend to occur in highly reflective (base-scan elevation) regions N or NE of the mesocyclone....thereby suggesting a link between large hail and +CG flashes. On the other hand, -CG dominated storms (found on the warm side of the boundary and further east on the cool side of the boundary) produce a large fraction of their flashes to the SE of the mesocyclone path (within a smaller reflectivity region at the base scan).
Large differences are found in the total number of +CG flashes between supercells producing significant tornadoes. The radar parameters herein fail to explain this difference.
There is evidence that the +CG dominated supercells not only experience enhanced CAPE and low-level shear as they cross the boundary but may also be in a region of shear and a left-curving hodograph between 9 and 12.5 km (AMA sounding)....consistent with the visual observations that place the storms toward the low-precipitation to classic end of the supercell spectrum.
Comparisons between radar characteristics will be shown for the observed and simulated supercells. Supercells are simulated in homogeneous environments and simplified non-homogeneous environments.
Session 2, Supercells and their environments
Wednesday, 12 January 2000, 9:30 AM-11:30 AM
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