Warm Season Lightning Distributions over the Northern Gulf of Mexico Coast and Their Relation to Synoptic-Scale and Mesoscale Environments

Abstract

Cloud-to-ground lightning data from the National Lightning Detection Network are used to create a warm season (May-September) lightning climatology for the northern Gulf of Mexico coast for the 14-yr period 1989-2002. Each day is placed into one of five flow regimes based on the orientation of the low-level flow with respect to the coastline. This determination is made using the vector mean 1000-700-hPa wind data at Lake Charles and Slidell, Louisiana. Flash densities are calculated for daily, hourly, and nocturnal periods.Spatial patterns of composite 24-h and nocturnal flash density indicate that lightning decreases in an east-to-west direction over the region. Flash densities for the 24-h period are greatest over land near the coast, with relative maxima located near Houston, Texas; Lake Charles, Baton Rouge, and New Orleans, Louisiana; Biloxi, Mississippi; and Mobile, Alabama. Flash densities during the nocturnal period are greatest over the coastal waters.Lightning across the northern Gulf coast is closely related to the prevailing low-level synoptic flow, which controls the sea breeze, the dominant forcing mechanism during the warm season. Southwest flow, the most unstable and humid of the five regimes, exhibits the most flashes. In this case, sea-breeze-induced convection is located slightly inland from the coast. Northeast flow, the driest and most stable of the regimes, exhibits the least amount of lightning. The large-scale flow restricts the sea breeze to near the coastline.Geographic features and local mesoscale circulations are found to affect lightning across the region. Geographic features include lakes, bays, marshes, swamps, and coastline orientations. Thermal circulations associated with these features interact with the main sea breeze to produce complex lightning patterns over the area.

Urban-induced thunderstorm modification in the Southeast United States

“…Across most reflectivity categories, Jackson rural and urban buffers had no significant differences in the means or medians, which confirms the initial hypotheses that the Jackson urban area is perhaps too small to modify thunderstorms or is masked by other circulations and convergence mechanisms induced by non-urban LULC effects. While Jackson is relatively close (250 km) to the Gulf of Mexico, there appears to be little evidence that the sea-breeze effect (Gibson and Vonder Haar 1990;Smith et al 2005) extends this far inland recurrently and, therefore, is influencing the climatology found herein.…”

Summertime Precipitation Regimes Associated with the Sea Breeze and Land Breeze in Southern Mississippi and Eastern Louisiana

“…As pointed out by Smith et al (2005), southeastern Louisiana is composed of flat marshland surrounded by Gulf waters that would tend to suppress the cross-shore $T. If we assume that the air temperature 4 km offshore of these shoreline points, or 8 km from KGPT and KBVE, is equal to the air temperatures observed by the nearest reliable buoy stations (42007 and 42040, respectively), then the resulting $T calculated along these 8-km crossshore segments may better depict the intensity of the local SBC and LBC.…”

The Intracloud Lightning Fraction in the Contiguous United States

“…When supplemented by coastal landmass heating, conditions are ideal for strong convection (Stroupe et al 2004). The timing and modulation of lightning in this area is driven by several flow regimes, as described by Smith et al (2005). There are also regions of high flash density over Florida.…”