Electron precipitation events driven by lightning in hurricanes

In mid-September of 2003, Hurricane Isabel passed through the Great Circle Path (GCP) of a subionospherically propagating LF signal between the NAU transmitter in Puerto Rico and a receiver located outside Boston. Cloud-to-ground lightning flashes detected by the Long-Range Lightning Detection Network (LRLDN) and located in the outer rainbands of the hurricane were associated with perturbations in the received LF signal consistent with lightning-induced electron precipitation (LEP) events. The number of perturbations, detected on the LF signal, exhibiting the known characteristics (rapid onset followed by slow recovery) of LEP events tended to increase with the occurrence of hurricane-associated lightning near the GCP. The majority (>65%) of causative lightning flashes (those flashes recorded in the LRLDN data that were time-correlated with spherics associated with LEP events in the VLF/LF data) occurred within 500 km of the GCP; and those flashes associated with Isabel typically occurred in the outer rainbands of the hurricane. While lightning generally occurs more frequently in the outer rainbands of hurricanes than in other tropical oceanic storms, there is no indication that the hurricane-associated lightning is more likely to induce electron precipitation events than lightning associated with other storm systems. Hurricane Floyd (in September of 1999) and Hurricane Fabian (in August/September of 2003) also passed near the GCP of subionospherically propagating VLF/LF signals, and the received signals exhibited similar perturbation patterns.