Type of Document Thesis Author Stroupe, Jessica Raye URN etd-11122003-172932 Title Warm Season Lightning Distributions Over the Northern Gulf of Mexico Coast and Their Relation to the Mesoscale and Synoptic Scale Environments Degree Master of Science Department Meteorology, Department of Advisory Committee
Advisor Name Title Henry E. Fuelberg Committee Chair Guosheng Liu Committee Member Philip Cunningham Committee Member Keywords
- National Lightning Detection Network
Date of Defense 2003-11-10 Availability unrestricted AbstractCloud-to-ground lightning data from the National Lightning Detection Network during the 14-year period 1989-2002 are used to create a warm season lightning climatology for the northern Gulf Coast. Days are separated into five flow regimes based on the orientation of the coastline and the low-level flow. Specifically, each day is classified into either a calm (less than 2.5 m s-1) or directional flow category based on the mean 1000-700 hPa vector wind data at Lake Charles and Slidell, Louisiana. Flash densities are calculated, and maps are created for daily, hourly, and nocturnal periods.
The composite 24-hour and nocturnal flash density maps indicate an east-to-west decrease in lightning over the region. Flash densities for the 24-hour period are greatest over land, with relative maxima located near the major metropolitan areas of Houston, Lake Charles, Baton Rouge, New Orleans, Biloxi, and Mobile. Flash densities during the nocturnal period are largest over the coastal waters. Land breezes, warm and shallow Gulf of Mexico waters, and advection of land-forming convection are responsible for the nighttime offshore convection.
Lightning across the northern Gulf Coast depends largely on the prevailing synoptic flow. The low-level flow controls the sea breeze, the dominant forcing mechanism during the warm season. Southwest flow is the most unstable and humid of the five regimes, and it exhibits the most flashes. In this case, sea breeze induced convection is located slightly inland from the coast. Northeast flow, being the driest and most stable of the regimes, exhibits the least amount of lightning. The large-scale flow holds the sea breeze along the coastline.
Flash density maxima over urban areas are examined to determine the relationship between lightning and the low-level flow. Analyses reveal that these maxima result from interactions between the prevailing flow and one or more mesoscale circulations. Urban influences such as frictional convergence, heat island effects, and air pollution also play a role in the enhancements.
Geographic features and local mesoscale circulations affect lightning across the northern Gulf Coast. Geographic features, including lakes, bays, marshes, swamps, and coastline orientations, interact with the low-level flow and mesoscale circulations, such as the sea breeze and lake breezes, to produce complex lightning patterns and distributions. This climatology is useful for operational meteorologists faced with the challenge of forecasting summertime convection and its resulting lightning.
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