Detection of Energetic Auroral Precipitation via VLF Remote Sensing

Abstract:

From 2003-2005, Stanford University operated a VLF beacon at South Pole station at 19 kHz. That may sound simple but that involved erecting a 6.7-km long antenna, no small feat in the harsh icy conditions of the South Pole.

The reason this massive undertaking was pursued was for the promise of VLF remote sensing of energetic (>30 keV) auroral precipitation. The idea was to detect the transmitted signal at various locations around the outer edge of Antarctica. VLF waves reflect off the lower ionosphere (60-90 km), and as such are highly sensitive to >30 keV electron precipitation, which disturbs the D-region ionization and thus perturbs the signal at some distant receiver. The network of VLF receivers around the edges of Antarctica could in principle provide longitudinal snapshots of where precipitation was occurring, at least during nighttime. While the South Pole VLF beacon worked well, the signal level was too weak at many of the sites, and as such the effort was largely unsuccessful, yielding only one paper with fairly weak results.

Georgia Tech has revived much of the data from that experiment, and made it publicly available via WALDO: the World Archive of Low-frequency Data and Observations (http://waldo.world). Georgia Tech has recently reanalyzed some of that old data, and applied some advanced noise subtraction algorithms. Upon further analysis, it turns out that the South Pole beacon signal is much more detectable, with much higher SNRs, than was previous thought. Previous studies required many minutes of integration to see the signal, which rendered it useless to detect precipitation that may occur on second or sub-second timescale. With our new noise subtraction techniques, we can see the signal on much shorter integration times, perhaps allowing us to fulfill the original goals of the massive effort, albeit 15 years late.

In this talk, we will reintroduce this forgotten yet highly useful dataset, present our exciting reanalysis, and illuminate a path forward to quantify the flux of energetic particles in the polar regions using VLF remote sensing.