85th AMS Annual Meeting

Tuesday, 11 January 2005: 4:00 PM
Dissecting the anomaly—A closer look at the documented enhancement in summertime ground flash densities in and around the Houston area
Michael L. Gauthier, University of Alabama, Huntsville, AL; and W. A. Petersen, L. D. Carey, and R. E. Orville
Poster PDF (1.9 MB)
This study uses nine years of National Lightning Detection Network (NLDN) data (1995-2003) to examine the regional variability of CG lightning flash density in south-central and southeastern Texas. In particular, we extend the results of previous studies that have focused on the Houston metropolitan “lightning anomaly”. We find, as in the previous studies, that there is a robust local maximum in CG lightning flash density over the Houston area. However, we also find that the Houston “anomaly” is a non-unique feature in CG lightning trends along the southeast coast. Indeed, numerous areas of enhanced mean and variance of the flash are located along the southeastern coast of Texas and Louisiana. Many of these local enhancements appear to be collocated with irregularities in the coastline including coastal region lakes, in addition to urban areas.

Specific to the Houston anomaly, our findings indicate that the spatial excess in CG flash density over Houston is a robust feature, even if days with flash densities exceeding the upper quartile of the highly skewed cumulative flash density distribution for our gridded domain are removed (this subset comprises less than 10% of the total daily sample, but produces 75-85% of the total lightning in the Houston area). This is also somewhat true of the surrounding coastal region, pointing to the importance of spatial preference in storm frequency in the determination of regional CG lightning anomalies.

By comparison, when examining inland regions (e.g., toward Dallas) we found that even fewer large events produced 80-85% of the total flash density. When only “lightning-days” were averaged to produce a conditional mean, we found that the CG anomaly still existed in the Houston area but that the conditional mean flash density became even larger moving inland into central Texas. The combined findings suggest that although the Houston area sees an increased frequency of lightning producing storms (including more large flash density events), storms occurring further inland (e.g., vicinity of Dallas), may actually produce more lightning on an event basis.

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