Electric field and microphysics of hurricanes

The Tropical Cloud Systems and Processes (TCSP) project was a campaign to primarily study tropical storm and hurricane genesis, based in San José, Costa Rica, during July 2005. The main research platform was a NASA ER-2, high altitude (~21 km) aircraft, which carried a number of instruments, including the Lightning Instrument Package consisting of electric field mills and an air conductivity probe, two Doppler radar systems, and the Advanced Microwave Precipitation Radiometer (AMPR). The field mills allow us to determine the vector electric field along the aircraft path. The AMPR allows us to determine ice particle concentration in the cloud beneath the aircraft using passive microwave ice scattering signatures. TCSP was the third program in which we have measured electrification above hurricanes. In the previous programs, we have found oceanic hurricanes to be at most only weakly electrified with little or no lightning in the central part of the storm. During the flight over Hurricane Emily (17 July 2005) we found strong electrification and significant lightning flash rates (over 9 flashes/min) in the eye wall. The ER-2 made several passes over and around the eyewall of Hurricane Emily during the flight. During the overpasses, the hurricane was almost constantly producing lightning. Vaisala's long range lightning detection system indicated that this remarkable lightning activity in the storm core persisted for several hours. We present the vector electric field, lightning rates, passive microwave microphysics, and Doppler radar data from Hurricane Emily and compare these observations with data from other hurricanes we have studied. We will address the question as to why Hurricane Emily was electrically so different from the other tropical storms.