Remote sensing of ionospheric disturbances associated with energetic particle precipitation using the South Pole VLF beacon

Abstract

[1] The Stanford University VLF beacon transmitter located at South Pole operates at 19.4 kHz, transmitting for 1 min intervals every 15 min throughout the day. The beacon serves as a tool to measure changes in the D region ionospheric conductivity owing to energetic particle precipitation and is capable of providing coverage that spans the Antarctic continent. We present VLF beacon signal amplitude and phase data measured at Palmer Station, Antarctica. Diurnal and seasonal variations are discussed first, followed by analysis of data from two periods of high geomagnetic activity, in July 2004 and in May 2005, with a phase advance and an amplitude depression of the beacon signal (as recorded at Palmer) observed for both cases. Data from the MEPED instrument aboard the NOAA-16 and 17 POES satellites show an increase in energetic electron (>100 keV) and proton (>16 MeV) precipitation fluxes coincident with the VLF beacon signal perturbations. The fluxes measured on POES are used as an aide to generate profiles of secondary ionization along the great circle path from South Pole to Palmer. These profiles are then applied to a quantitative model of subionospheric VLF signal propagation to estimate the phase and amplitude variations expected. Results indicate that the observed VLF amplitude and phase data are in reasonable agreement with theoretical calculations in both cases, indicating that the model captures the ionospheric disturbance in effect during both of the disturbed periods.