Causes of HF Backscatter Loss During Large Geomagnetic Storms: Comparisons between Northern and Southern Hemisphere SuperDARN Radars

Abstract:

HF communication and surveillance systems are known to experience difficulty during geomagnetic storm conditions. The Super Dual Auroral Radar Network (SuperDARN) comprises over 35, HF (8-12 MHz) over-the-horizon radars used to study ionosphere dynamics and HF propagation. It is well known that SuperDARN radars experience a loss of backscatter during geomagnetic storm events, yet details of the reasons why this occurs are not clear. Loss of HF backscatter during geomagnetic storms is often attributed to D region absorption. However, the data shows that during intense geomagnetic storms, SuperDARN radars return high signal/noise ratio, backscatter from ranges out to ~800 km, inconsistent with loss due to absorption in the D region. Examples of SuperDARN backscatter during large storms will be presented and discussed together with HF ray-tracing, ionosonde and riometer data. Data from Kodiak in the north and Bruny Island in the south hemisphere are compared. These reveal properties of the ionosphere as the storm progresses and show hemisphere similarities and differences. Possible backscatter loss mechanisms will be discussed, given the evidence derived from the experimental data.