Radar Reflectivity Signatures Associated with the Enveloped Eyewall Lightning Signatures of 2016 Super Typhoons Nepartak and Meranti

There are a number of strategies to monitor the strength and track of tropical cyclones, with some dependent on their proximity to land and national meteorological resources. Among these monitoring methods are aircraft reconnaissance and satellite. Aircraft reconaissance is typically limited to the Atlantic Basin. Satellite data are available globally, and allow forecasters to monitor tropical cyclone development, strength, and track far from land, but can have a coarse temporal and spectral resolution. As a tropical cyclone approaches land, forecasters can use radar for higher resolution monitoring of intensity and track, including Doppler estimates of wind speed and tracking of convective elements within the eyewall and outer bands. These convective elements can have greater impacts if they make landfall, including higher wind speeds, greater rainfall, and occasionally tornadoes. In recent years, long range lightning location systems have enabled forecasters to monitor convective elements in tropical cyclones around the world in near real-time. Since these long range lightning location systems are a relatively new sensing method for tropical cyclones, it is important to compare their data to more conventional data to understand how it can be used to support the monitoring of tropical cyclones.

Vaisala's Global Lightning Dataset GLD360 has a flash detection efficiency of approximately 70 percent across the Northwest Pacific Basin, providing highly detailed observations of tropical cyclone lightning events. GLD360 has allowed the discovery of a unique lightning signature within the eyewall of a few very significant tropical cyclones, named the Enveloped Eyewall Lightning (EEL) signature. This signature refers to lightning that completely envelops the eyewall, and persists for at least six hours. Here, we present two tropical cyclones, Super Typhoon Nepartak and Super Typhoon Meranti of 2016 that occured in the western Pacific Ocean with the EEL signature, and their corresponding radar reflectivity images. The radar data for each of these storms shows a nearly completely circular annulus of high reflectivity surrounding the eye where the enveloped lightning is occurring. While the mechanisms behind the EEL signature are not yet fully understood, the side-by-side comparison of radar and lightning data can help enhance the understanding, and give forecasters another tool to monitor the track and intensity of a tropical cyclone.