An Analysis of the Performance of the Houston Lightning Mapping Array During an Intense Period of Convection During Tropical Storm Harvey

Abstract

AbstractExtreme lightning activity (∼300,000 flashes) was observed by the Houston Lightning Mapping Array (HLMA) network during Tropical Storm Harvey on August 26, 2017–August 27, 2017. There was an overall weak correlation between the lightning flash and precipitation rates (R = 0.14; p ∼ 0.17) likely due to feeder bands transitioning between deep and shallow convection. The peak precipitation rate (14.2 mm hr−1) lagged the peak lightning flash rate (∼18,000 flashes [30 min]−1) by 7 h. Adjusting for the lag, the correlation increased to 0.71 (p < 0.01) indicating a relationship between the uptick in lightning activity in the convective feeder bands and the resulting heavy precipitation during episodes of shallow convection. Peak lightning flash extent densities of 12.4 km−2 min−1 were spatially collocated with precipitation rates exceeding 9 mm hr−1. NEXRAD reflectivity data featured 30 dBZ echo heights in excess of 10 km that were collocated with peak lightning flash extent densities exceeding 3 km−2 min−1. The NEXRAD specific phase (kdp) and differential phase (Zdr) dual‐polarization products were highest (≥2° km−1 and dB) below the melting layer (4.6 km) indicating heavy precipitation and strong updrafts. Negative kdp and Zdr values (≤−0.15° km−1 and dB) collocated with the peak lightning flash extent density altitudes indicated ice particle generation which likely augmented the charge separation process. This is likely the first time a major tropical cyclone has occurred within the confines of a lightning mapping array. The lightning data, when used synergistically with radar and precipitation data, can adequately quantify tropical convection exhibiting an elevated mixed‐phase depth.