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. This study explores relationships between lightning, cloud microphysics, and TC storm structure in rapidly intensifying Hurricane Karl (16 September 2010) using data collected by the NASA DC-8 and Global Hawk (GH) aircraft during NASA's Genesis and Rapid Intensification Processes (GRIP) experiment.;The study capitalizes on the unique opportunity provided by GRIP to synthesize multiple datasets from the two aircraft and analyze the physical properties of an electrified TC. The Lightning Instrument Package (LIP, GH) measured electric fields and provided in situ information about both cloud-to-ground and intracloud lightning. The LIP-derived lightning data were supplemented by information from two ground-based lightning networks---the World Wide Lightning Location Network (WWLLN) and the Vaisala Global Lightning Dataset (GLD360). Microphysics probes on the DC-8 provided particle concentrations and 2-D images of hydrometeors ranging from 0.35 to 6200 mum. Ku-band reflectivities from the Airborne Precipitation Radar (APR-2, DC-8) and High-Altitude Imaging Wind and Rain Airborne Profiler (HIWRAP, GH) were used with brightness temperatures from the High-Altitude Monolithic Microwave Integrated Circuit (MMIC) Sounding Radiometer (HAMSR, GH) to assess Karl's convective structure. Flight level vertical velocities from the Meteorological Measurement System (MMS, DC-8) and Doppler velocities from APR-2 provided information about Karl's convective updrafts.;We analyze five coordinated flight legs through Karl by the DC-8 and GH, focusing on the inner core region (within 50 km of storm center) where most of the lightning was concentrated and the aircraft were well coordinated. The non-inductive charging mechanism that is believed to produce storm electrification requires ice and graupel collisions in the presence of supercooled water. The GRIP data are used to compare properties of electrified and non-electrified inner core regions that are related to this charging mechanism.;MMS and APR-2 reveal that although the majority of inner core updrafts were weak (96.6% < 5 m s-1), the electrified regions typically contained peak updrafts exceeding 10 m s-1. Conversely, the non-electrified regions generally were associated with weaker updrafts that peaked around 5--6 m s-1. Microphysical measurements indicate that enhanced concentrations of small ice particles often were associated with the stronger inner core updrafts. These large concentrations likely corresponded to regions of recently frozen, homogeneously nucleated ice particles. Thus, the presence of supercooled water below the aircraft was inferred from the microphysical data collected at flight level. Reflectivities from APR-2 and HIWRAP show that the electrified regions of flight legs contained enhanced reflectivities in the mixed phase region, thereby indicating that supercooled water and/or large ice particles were carried aloft by strong updrafts. A deep mixed phase region is known to be crucial for charge separation and storm electrification.;Case studies of two electrified legs are presented to further analyze the convective environments that produced lightning in Karl's inner core. The GRIP aircraft sampled a deep convective burst and a broad convective region during these two legs. Despite the structural differences between the convection sampled on these legs, we identified three common characteristics of Karl's electrified regions: (1) strong updrafts of 10--20 m s-1 , (2) deep mixed phase layers indicated by reflectivities > 30 dBZ extending several km above the freezing level, and (3) microphysical environments consisting of graupel, very small ice particles, and the inferred presence of supercooled water. These characteristics describe an environment where non-inductive charging and TC electrification are expected. We conclude that the electrified regions in Karl's inner core were attributable to a microphysical environment that was conducive to electrification due to occasional, unusually strong convective updrafts in the eyewall.