GLM Flash Data Trends during Tropical Cyclone Intensification Changes
Pequeen, David Jeffrey
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Using lightning as an indicator for tropical cyclone (TC) intensity change has been a subject of investigation for more than 25 years. While the general TC radial flash distribution is well-characterized in the literature, the position of inner-core lightning bursts (ICLB) relative to the radius of maximum wind (RMW) as an instructive factor in forecasting 24-hour storm intensity change is a recent development. The Geostationary Lightning Mapper (GLM) aboard the Geostationary Operational Environmental Satellite (GOES) has added continuous coverage of intracloud and cloud-to-ground flashes for tens of TCs in both the eastern north Pacific (ENP, observed by GOES-17) and north Atlantic (NA, observed by GOES-16) ocean basins. This analysis will provide an overview of 194 two-hour ICLB activity periods in non-landfalling conditions from 14 TCs (seven from 2018-2019 NA TCs; seven from 2019 ENP TCs) and explore the joint distribution of flash rate, area, and energy properties as a function of TC intensity change, radial distance, and time. This GLM dataset supports several previous conclusions in the TC literature, including that NA TCs tend to have greater flash density than ENP TCs, weaker TCs tend to have more flashes than stronger TCs, the presence of an ICLB alone is not sufficient to inform intensity change forecasts, and lightning in any given TC is episodic. Interior to the RMW, ICLBs preceded an average 24-hour strengthening of +9.07 kts. Extending outside the RMW, ICLBs preceded a slight preference for 24-hour weakening between 1 and 1.5 RMW (-2.84 kt) and a stronger preference for 24-hour weakening beyond 1.5 RMW (-9.04 kt). Upcoming periods of rapid intensification were better predicted by the RMW relationship established in the literature than upcoming rapid weakening. Additionally, three TCs produced extended, long-duration (>15 hour) periods of nearly continuous flashes approximately at the RMW. Slight variations in the range of lightning during these times implies the potential to use lightning as another indicator of RMW variability.