Investigating Possible Causative Mechanisms behind the Houston Cloud-to-Ground Lightning Anomaly

Previous studies have demonstrated that, in a regional context, the Houston cloud-to-ground (CG) lightning anomaly is a non-unique feature, embedded within the larger-scale enhancement of CG lightning along the Texas and Louisiana Gulf Coasts, and that inland cities like Dallas see far more CG lightning on a per-event basis. Despite the fact that the Houston area is located at the western edge of this coastal enhancement, it has been shown that this anomaly is a persistent summer-season feature with flash densities over and downwind of the Houston metropolitan area on the order of 1.5-2 times that of it's immediate surroundings.

Primary hypotheses offered to explain this documented enhancement in summer-season CG lightning revolve around "urban" effects. Specifically: (1) enhanced convergence, thermodynamic instability, or dynamical influences associated with the urban heat island; (2) altered microphysical processes associated with anthropogenic pollution; and/or (3) mesoscale enhancements in sea breeze convergence. Although these hypotheses are neither new, nor are they individually unique to the Houston area, a comprehensive field campaign has yet to be conducted to fully explore these possible causative mechanisms.

In an attempt to better isolate and address the feasibility of each of the above hypotheses in explaining the climatalogical lightning anomaly over the Houston area, this paper utilizes data from 3 separate archived datasets (CG lightning, surface observations (winds and temperature) as well as pollutant measurements from EPA and TCEQ sources).

Preliminary results indicate that daily CG flash counts over the Houston area are positively correlated with urban heat island and sea breeze intensities, as in hypotheses 1 and 3 above. Contrary to hypothesis 2 however, we did not observe a correlation between pollutant concentrations and CG lightning activity indicating that the lightning anomaly over the Houston area is likely the atmosphere's response to enhanced, localized forcing over the area.