Tropical Cyclone Intensity Change from a Lightning Perspective

Despite many studies over the last few decades on tropical cyclone (TC) intensity changes following lightning outbreaks, a dichotomy still exists in the literature on the sign of the 24-h intensity change. Lightning is most frequent in two TC radial regions: the inner core (IC; ~0-100 km) and the outer rainbands (OB; ~200-300 km). Large OB lightning flash rates are consistently associated with intensifying TCs; however, IC lightning outbreaks have been observed in both weakening and intensifying TCs. This study analyzes both IC and OB lightning outbreaks using the World Wide Lightning Location Network (WWLLN) on a spatial grid similar to the Geostationary Operational Environmental Satellite Series-16 (GOES-16) Geostationary Lightning Mapper (GLM).

Three hypothesized influences on TC intensity change were tested for IC lightning outbreaks: 1) the intensity change 24 h prior to the outbreak, 2) the azimuthal location relative to the deep-layer (850-200-hPa) vertical wind shear, and 3) the radial location relative to the Extended Flight Level Dataset for Tropical Cyclones (FLIGHT+) radius of maximum wind (RMW). IC lightning outbreaks radially inside the RMW, as well as a weaker signal of outbreaks azimuthally upshear, were associated with TC intensification.

The relationship between OB lightning and TC intensity change, although consistent in the literature, contradicts other studies that find strong convection in the OB region has negative influences on TC intensity. Since OB lightning is suggested to be a signal of the favorability of the environment in which the TC is embedded, the convective available potential energy (CAPE) was compared between TCs with and without OB lightning outbreaks. Additionally, OB lightning outbreaks were analyzed for a relationship to internal TC dynamics (e.g., secondary eyewalls). Hurricanes Earl and Karl (2010) were chosen for further analysis from both an observational and modeling perspective to better understand differences between electrified and non-electrified convection in the OB.