Subionospheric early VLF perturbations observed at Suva: VLF detection of red sprites in the day?

Abstract

First observations of early Very Low Frequency (VLF) perturbations on signals from NWC (19.8 kHz) and NPM (21.4 kHz) monitored at Suva, in the month of November 2006, are presented. The early/fast, early/slow, early/short (RORD), and step‐like early VLF perturbations are observed on signals from both the transmitters. The early/fast VLF events are found to occur more often in the nighttime than in the daytime whereas step‐like early events predominantly occur in the daytime. Most of the early VLF events are associated with amplitude changes between 0.2–0.8 dB with only a few cases > 0.8 dB. In general, the recovery time of daytime early/fast VLF events is less when compared to the nighttime early/fast VLF events. The lightning location data provided by the World‐Wide Lightning Location Network and broadband VLF data recorded at Suva have been analyzed to identify the location of causative lighting discharges along the great circle paths between transmitter and receiver, and the sferics associated with causative lightning of early VLF events. This research is the first to report both daytime early/fast VLF perturbations with faster recovery and also step‐like early VLF perturbations initiated and ended by the lightnings which are most likely associated with red sprites and/or elves occurring in the daytime.