Understanding the Relationships Between Lightning, Cloud Microphysics, and Airborne Radar-Derived Storm Structure during Hurricane Karl (2010)

The sporadic nature of lightning in tropical cyclones (TCs) is a topic of great interest to researchers and forecasters. The frequency and spatial distribution of lightning within Hurricane Karl were highly variable during the storm's rapid intensification (RI) on 16 September 2010. This paper describes relationships between lightning, cloud microphysics, and TC storm structure using data gathered from flights into Karl on 16 September during NASA's Genesis and Rapid Intensification Processes (GRIP) experiment. The objective was to obtain a better understanding of the factors contributing to the presence or absence of lightning in TCs and thereby better understand the information that lightning data convey about a storm.

Several GRIP datasets have been synthesized to analyze Karl's structural evolution during RI. Reflectivity, Doppler velocity, and depolarization data from the dual-frequency Airborne Precipitation Radar (APR-2) were used to study Karl's vertical structure and infer the shape/phase of particles present in different regions of the storm. The various microphysics probes on the DC-8 provided valuable measurements of particle size distributions and ice water content. The Lightning Instrument Package (LIP) aboard the Global Hawk measured electric fields and provided in situ information about both cloud-to-ground and intracloud lightning. Time series of relevant meteorological, microphysical, and radar-derived parameters have been created to analyze how the different fields are related to the observed lightning patterns. These datasets were used to compare electrified vs. non-electrified flight legs and physically explain the spatial and temporal variations of lightning observed in Karl.