Diurnal Pulsing of Lightning in Strong Tropical Cyclones

Recent work has shown that mature tropical cyclones exhibit a pattern of diurnal pulsing in the infrared (IR) cloud field when GOES imagery is transformed into local standard time (LST). The pulses, which appear as “cool rings” in the six-hour IR difference images, begin forming near the center of the tropical cyclone at sunset each day and propagate outward several hundred kilometers overnight. Since the IR band senses cloud tops, it is not known whether these cool pulses are cirrus cloud reflections confined to the upper troposphere, or whether the pulses are tied to processes, such as convection, affecting a deeper layer of the troposphere. The goal of this study is to employ the World Wide Lightning Location Network (WWLLN) to determine if these pulses are associated with electrically active, deep convection.

This study examines all major hurricanes from 2005 to 2012 in the Eastern North Pacific and North Atlantic basins using the WWLLN. When the lightning is transformed into LST, a clear diurnal signal is revealed in the tropical cyclone lightning frequency. This signal begins near the center around local midnight, and propagates outward several hundred kilometers through local noon. Some tropical cyclones have a very strong lightning signal associated with these pulses, while others do not. In addition to demonstrating the clear diurnal pulse in the composite lightning data, an analysis of why certain tropical cyclones do not have a clear diurnal signal will be explored.