Total lightning mapping, along with radar and NLDN cloud-to-ground lightning
data, can be used to diagnose the severity of a storm. Analysis of the 13 October 2001
supercell event (Dallas-Fort Worth, Texas), some supercells of which were tornadic,
shows that LDAR II lightning source heights (quartile, median, and 95th percentile
heights) increased as the storms intensified. Most of the total lightning occurred where
reflectivity cores extended upwards and within regions of reflectivity gradient rather
than in reflectivity cores. A total lightning hole was associated with an intense, nontornadic
supercell on 6 April 2003. This feature was nonexistent from all supercells
analyzed during the 13 October case.
During tornadogenesis, the radar and LDAR II data indicated updraft weakening.
The height of the 30 dBZ radar top began to descend approximately 10 minutes (2
volume scans) before tornado touchdown in one storm. Total lightning and CG flash
rates decreased by up to a factor of 5 to a minimum during an F2 tornado touchdown
associated with this storm. LDAR II source heights all showed descent by 2-4 km during a 25 minute period prior to and during this tornado touchdown. This drastic trend
of decreasing source heights was observed in two tornadic storms prior to and during
tornado touchdown, but did not occur in non-tornadic supercells, suggesting that these
parameters can be useful to forecasters. These observations agree with tornadogenesis
theory that an updraft weakens and the mesocyclone can become divided (composed of
both updraft and downdraft) when a storm becomes tornadic.
LDAR II source density contours were comma-shaped in association with severe
wind events within mesoscale convective systems (MCSs) on 13 October 2001 and 27
May 2002. This signature is similar to the radar reflectivity bow echo. Consistent
relationships between severe weather, radar and lightning storm characteristics (i.e.,
lightning heights) were not found for cells within MCSs as was the case for supercells.
Cell interactions within MCSs are believed to weaken these relationships as reflectivity
and lightning from nearby storms contaminate the cells of interest. It is also more
difficult to clearly define a cell within an MCS.
| Identifer | oai:union.ndltd.org:tamu.edu/oai:repository.tamu.edu:1969.1/4684 |
| Date | 25 April 2007 |
| Creators | Steiger, Scott Michael |
| Contributors | Orville, Richard E. |
| Publisher | Texas A&M University |
| Source Sets | Texas A and M University |
| Language | en_US |
| Detected Language | English |
| Type | Book, Thesis, Electronic Dissertation, text |
| Format | 7406798 bytes, electronic, application/pdf, born digital |
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