Observing Auroral Radio Emissions in Conjugate Hemispheres

In addition to its beautiful optical displays, the aurora produces radio emissions of various types, including cyclotron harmonic emissions, auroral hiss, medium frequency burst (MFB), and auroral kilometric radiation (AKR). These emissions enable remote sensing of ionospheric processes and provide a natural laboratory for studying physics of radio emissions that also occur in planetary, solar, and astrophysical environments. Similar to the optical aurora, these radio emissions are generated separately in the northern and southern hemispheres. Nevertheless, optical aurora sometimes exhibit similar features simultaneously in the two hemispheres because aurora in both hemispheres are ultimately driven by the interaction between the solar wind and the magnetosphere. The same should be true of radio emission. At very low frequencies (VLF), auroral hiss has previously been detected at conjugate observatories in Iceland and Antarctica, and satellite-borne radio receivers have observed AKR simultaneously emanating from conjugate sources; however, the other types of radio emission have never been studied at both ends of a magnetic field line. To accomplish this, LF/MF/HF radio receivers have recently been installed at Qikiktarjuaq and Iqaluit, Nunavut, observatories of the Canadian High Arctic Ionospheric Network (CHAIN) which straddle the nominal magnetic conjugate point of South Pole Station, Antarctica, where Dartmouth College operates LF/MF/HF receivers. The Arctic observations employ a dedicated 10-m^2 magnetic loop antenna with active preamp, and a feed from the horizontal linear dipole antennas used for reception of CHAIN ionosonde signals. The Antarctic observations use magnetic loops of areas 2.5-40 m^2 depending on frequency range. Both systems have collected data since October, 2022. Conjugate auroral hiss events have been detected in both equinoctial and solstice conditions. In the latter case, the hiss observed in the daylit hemisphere was weaker than that in the dark ionosphere. Based on initial data, the characteristics and seasonal dependence of conjugate LF auroral hiss appears consistent with previous observations at VLF. Many hiss and cyclotron harmonic emissions have been observed in one hemisphere but not the other. Upcoming 2023 Spring equinox will bring a period of simultaneous darkness at South Pole and Qikiktarjuaq ideal for conjugate medium frequency burst and cyclotron harmonic emissions.