Understanding the Relationship Between Lightning Outbreaks and Tropical Cyclone Intensity Change

Several recent studies have observed an association between intensity changes and lightning outbreaks in the tropical cyclone (TC) inner core (IC; ~0–100 km) and outer rainband (OB; ~100–300 km) regions. The sign of this relationship, however, is inconsistent among the studies and, at times, contradicts theory. This research aims to reconcile the discrepancies between previous studies by using data from the World Wide Lightning Location Network (WWLLN) and select aircraft reconnaissance missions to systematically examine the impacts of both IC and OB lightning on TC intensity change in North Atlantic and eastern North Pacific TCs.

No clear relationship exists in the literature between IC lightning and TC intensity change (studies have documented IC lightning bursts associated with both weakening and intensification). The first part of this study investigates three hypotheses that may influence the relationship between IC lightning and TC intensity change: 1) the prior TC intensity change, 2) the azimuthal location of the burst relative to the strength and direction of the deep-layer environmental vertical wind shear, and 3) the radial location of the burst relative to the radius of maximum wind.

Prior studies have noted higher OB lightning flash densities in intensifying TCs. One possible explanation is that the OBs can act as a source of potential vorticity that can be advected into the TC core. However, other studies have documented negative impacts on TC intensification, such as the OB's ability to: 1) act as an inflow barrier, 2) induce flow opposing the TC's secondary circulation, 3) reduce the equivalent potential temperature in the boundary layer inflow, and 4) hydrostatically reduce the radial pressure gradient. The second part of this study investigates the relationship between OB lightning and TC intensity change, and to what extent the previously documented opposing influences are present.