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.

Ultrarelativistic electrons in the near cosmos and X‐ray aurora in the middle polar atmosphere

“…Our conclusion about the nature of precipitation events, which is stated below, is founded on the indirect ground‐based measurements. Until now, we have had to rely on such measurements because (i) there have been no direct measurements of the precipitating highly relativistic electrons (HREs) in the polar region, (ii) monitoring of the HREs has been limited to less than ∼ 10 MeV energy electrons [ Baker et al , ; Demirkol et al , ; Chevalier et al , ], and (iii) the pioneering URE flux measurements at energies 10 2 −10 3 MeV were obtained for the inner radiation belt (L = 1.2 ‐ 2) [ Dmitrenko et al , ]. On the basis of abnormal variations of the amplitudes and phases of very low frequency (VLF) signals (10–16 kHz), recorded during continuous ground‐based measurements in the polar region in 1982–1992, experimental facts (i)–(iii) pointed above were established.…”

An autonomous receiver/digital signal processor applied to ground‐based and rocket‐borne wave experiments

“…As a result, the station is very favorable for studies of radio emissions of natural origin and hosts a variety of radio receivers at ELF to HF frequencies, complemented by other geophysical diagnostics such as all-sky cameras, photometers, and fluxgate magnetometers. Significant observations at VLF [Martin, 1960;Chevalier et al, 2007], LF-MF [LaBelle et al, 2005;Ye et al, 2006;Yan et al, 2013;Broughton et al, 2014], and HF [Rodger and Rosenberg, 1999;Patterson et al, 2001] have been made at the station.…”

Longitudinal dependence of lightning-induced electron precipitation

“…The amount of secondary ionization is then calculated by the often‐quoted factor of one electron‐ion pair created for every 35 eV of electron energy [ Rees , 1963]. Previous studies [e.g., Peter and Inan , 2007; Chevalier et al , 2007] have used a similar approach to determine the altitude profile of secondary ionization created by precipitating electrons. However, these studies emphasized the energy of the particle, generally ignoring the equally important contribution of incident pitch angle, or accounting for it only in a generalized sense.…”