Lightning Behavior as a Diagnostic Tool to Quantify the Strength and Evolution of Precipitation Processes During Tropical Convective Events over Southeast Texas
Abstract
Although Hurricanes Harvey (2017) and Nicholas (2021) both rapidly intensified before making landfall in the populous and highly convective region of southeast Texas, the tropical systems exhibited different lightning-precipitation characteristics. Given the inherent connection between lightning and precipitation, the utility of total lightning observations to diagnose the magnitude and evolution of precipitation processes during tropical convective events impacting southeast Texas is demonstrated. The continental outer rainbands of Harvey and the oceanic outer rainbands of Nicholas are studied for their lightning-precipitation microphysics using data from the Houston Lightning Mapping Array (HLMA) and the National Lightning Detection Network (NLDN) in synergy with radar, satellite, and other traditional products.
The behavior of the lightning activity discerned the state of the tropical convection and thus revealed how precipitation would occur, as electrified deep convective clouds feature brief periods of intense rainfall while less-electrified shallow clouds contain lower rainfall rates that are prolonged. Strengthening updrafts were also denoted by higher-altitude lightning and surges in flash rate. The peak flash extent and source densities were spatially correlated with the largest precipitation rates for the deep convection within Harvey and Nicholas, yet the shallow convection portrayed these maxima to be offset. There was a temporal lag between the highest flash and rainfall rates, with lightning (~300 fl min^-1) preceding precipitation (9 mm hr^-1) by 5.5 hours during Harvey and precipitation (6.5 mm hr^-1) preceding lightning (~28 fl min^-1) by 2.8 hours during Nicholas. The majority of lightning activity occurred after landfall during Harvey and before landfall during Nicholas. Lightning measurements collected during Harvey were about two orders of magnitude greater than those of Nicholas with maximum flash extent densities (fl km^-2 min^-1) at ~900 versus ~14, largest VHF source densities (src km^-1 {5 min}^-1) at 56.7 versus 1.4, and highest VHF source rates (src {5 min}^-1) at 177,472 versus 3,250. Harvey’s continental convection was more powerful and organized than Nicholas’s oceanic convection with widespread lightning-precipitation spatial and temporal coverage, inverted tripole charge layers located at higher heights, and larger ZH (55-63 dBZ), ZDR (> 1.5-2 dB), and KDP (> 2.5-3 deg km^-1) values surpassing the melting level.
Subject
lightningprecipitation
tropical cyclones
microphysics
convection
radar
satellite
intensification
Citation
Butler, Sydney Nicole (2023). Lightning Behavior as a Diagnostic Tool to Quantify the Strength and Evolution of Precipitation Processes During Tropical Convective Events over Southeast Texas. Master's thesis, Texas A&M University. Available electronically from https : / /hdl .handle .net /1969 .1 /198891.