Dayside auroral hiss observed at South Pole Station

Abstract

We performed a statistical study of low frequency (LF) auroral hiss recorded at South Pole Station in 2004, 2005, and 2007, and very low frequency (VLF) hiss recorded in 2000–2008. As expected, most auroral hiss occurs in the pre‐midnight sector. However, there is a secondary peak in occurrence in the pre‐noon sector (1000–1530 UT; ∼ 0630–1200 magnetic local time (MLT)) and somewhat more events occur in the post‐noon sector (1530–2100 UT; ∼ 1200–1730 MLT), with a null in occurrence around noon MLT. Individual dayside events appear similar to nightside hiss, but statistically they do not extend to as high frequencies. Solar wind discontinuities or impulses on the magnetopause are not correlated with these events. All‐sky camera, photometer, magnetometer, riometer, and VLF receiver data show that dayside LF hiss almost always extends to the VLF range and is often associated with active aurora. Examination of interplanetary magnetic field (IMF), substorm conditions, and Kp/AE/QI indices at times of dayside hiss suggests differences between the pre‐noon and post‐noon events: pre‐noon events are associated with IMF By < 0, whereas post‐noon events favor Bz < 0 and show a weaker correlation with By > 0. The correlation between pre‐noon events and By < 0 may arise because under those conditions, the pattern of field‐aligned currents (FACs) shifts to later magnetic local times, causing upward FACs to be dominant during pre‐noon hours at 74°, the invariant latitude of the South Pole. Unlike pre‐noon events, post‐noon events are more often associated with substorm activity on the nightside and favor elevated Kp indices, suggesting a connection of post‐noon events to nightside activity.