Direction Finding of Auroral Radio Emissions: Simultaneous Observations and Ray Tracing of Medium-Frequency Burst and Hiss

Auroral radio emissions play a key role in remotely sensing Earth's magnetospheric and ionospheric plasma conditions. These emissions are particularly valuable because they exhibit characteristics similar to those observed in a wide range of planetary and astrophysical environments, offering broad insights into space plasma processes. Among the various types of emissions, notable examples include auroral hiss, medium-frequency bursts (MFB), cyclotron harmonic emissions, and auroral kilometric radiation. Hiss refers to a very low frequency (VLF) to low frequency (LF) whistler-mode emission that typically originates at altitudes ranging from several hundred to several thousand kilometers. In contrast, MFB spans the 1.5 to 4.5 MHz range and is generally believed to originate in the topside ionosphere. Although MFB and hiss are frequently observed and well documented to coincide in time, the extent of their spatial correlation remains an open question, requiring further investigation.

This study focuses on examining the directions of arrival of simultaneously observed MFB and hiss emissions. We utilized data collected between 2013 and 2017 by a five-antenna radio array located in Sondrestrom, Greenland (73.3° magnetic latitude), in conjunction with 2D, 3B ray tracing software to estimate signal propagation paths. Direction-finding techniques were used to determine the azimuth and elevation angles of arrival, with the goal of assessing whether these emissions may originate from the same auroral arc structure. Variations in angles of arrival across time and frequency were statistically analyzed to identify spatial trends. Additionally, ray tracing combined with electron density profiles observed from the Sondrestrom ISR and implementation of PIC simulations will be used to estimate and compare relative source altitude extrema. These methods will allow for an evaluation of whether beam re-formation mechanisms could plausibly explain the simultaneous generation of both emissions by field-aligned electron beams.

The results of this study support the utility of ground-based observations for probing field-aligned electron beam dynamics and highlight the potential of MFB as a diagnostic tool for remotely sensing ionospheric conditions and processes.