The propagation of mixed polarization VLF (f ≤5 kHz) radio waves in the Antarctic Earth‐ionosphere waveguide

Abstract

During 1986, a series of special VLF transmissions at ~3 kHz and ~5 kHz were made from the crossed dipole antenna at Siple Station, Antarctica, which simulated transmissions from a single horizontal dipole at a number of different orientations. The subionospheric signals thus excited were recorded at four Antarctic stations: Faraday, Halley, South Pole and Arrival Heights (McMurdo Sound). The signals excited broadside to the dipole were seen to exhibit characteristics notably different from those of signals excited along the axis of the antenna, showing a minimum in received power (the depth of the minimum decreasing for the more highly attenuating paths) and increases in apparent arrival azimuth error and elevation angle. A simple computer model for mode propagation close to 5 kHz in the Antarctic Earth-ionosphere waveguide showed that these variations were the consequence of two effects: the preferential excitation of quasi-transverse magnetic (QTM) modes along the axis of the antenna and the lower attenuation of quasitransverse electric (QTE) modes (with respect to QTM modes) over the Antarctic ice sheet. These results have important implications for studies involving the subionospheric propagation of signals with frequencies at the lower end of the VLF band and over highly attenuating surfaces, showing that QTE modes play a significant and sometimes dominant role. The propagation characteristics derived from the model may be applied to studies of the effect of burst energetic electron precipitation on subionospheric VLF signals (the Trimpi effect). Furthermore, the mode structure of subionospheric VLF signals radiated from the Siple transmitter, or a similar facility in Antarctica, may be controlled through the appropriate choice of signal frequency and antenna arrangement. •Now at James Rennell Centre for Ocean Circulation, Southampton, England Paper number 92RS00908. 0084-6604 / 92 / 92RS-00908 $08.00 tica [Helliwell and Katsufrakis, 1978], namely, the excitation of signals at the low end of the VLF range (3 kHz 593 594 COTTON ET AL ß VLF PROPAGATION IN THE ANTARCTIC EARTH-IONOSPHERE WAVEGUIDE _< f _< 10 kHz) from a long horizontal dipole antenna situated on a thick, poorly conducting ice sheet, and their subsequent propagation between a variable highlatitude ionosphere and an ice sheet of spatially varying thickness, has been less extensively studied. This paper reports an experiment to investigate the problem, using a crossed dipole transmitting antenna arrangement at Siple and a network of Antarctic receiving stations and describes a simple computer model for waveguide mode propagation which was developed to interpret the experimental data obtained. The main motivation for the work is the possible use of such a network for remotely detecting and mapping the burst precipitation of energetic particles into the lower ionosphere through the resulting perturbation of subionospherically propagating signals (the Trimpi effect [e.g., Inan and Carpenter, 1987]). The region spanned by the network is linked by geom...

Characterization of terminal impedance and radiation properties of a horizontal VLF antenna over Antarctic ice

“…Over the past few decades, there has been interest in the study of VLF wave propagation within the Earth‐ionosphere waveguide in the Antarctic region. For instance, Cotton et al [1992] and Reznikov et al [1993] studied the effects of the ionosphere on attenuation and polarization changes for VLF waves propagating over the Antarctic terrain. Carpenter et al [1988] and Helliwell and Katsufrakis [1974] used the former Siple Station transmitter as a VLF wave injection instrument to probe regions of the ionosphere and magnetosphere.…”