Further evidence for a connection between auroral kilometric radiation and ground‐level signals measured in Antarctica

Abstract

AbstractInspired by recent observations of three cases of coincident ground‐level auroral kilometric radiation (AKR)‐like signals and outgoing AKR measured with the Geotail satellite, investigation of 2008 data from four Antarctic observatories yields >30 additional examples. The occurrence rate peaks near 22 MLT similar to that of AKR. Polarization measurements of one event show it to be right‐hand polarized. Correlation analysis of ground‐level and satellite data suggests an imperfect correlation with 2–3 sigma significance, although occasionally much better. (Perfect correlation is not expected, for at least two reasons: distant satellites detect AKR from many sources over a significant part of the oval, and many effects can hinder transmission of AKR from those sources to either distant satellites or ground stations.) Statistical analysis of the existing quantity of data is therefore suggestive but does not prove a connection between the ground‐level AKR‐like signals and outgoing AKR. However, two other methods provide evidence favoring such a connection. The first full‐resolution measurements of ground‐level AKR‐like signals show that their fine structure strongly resembles that of AKR as known from high‐resolution spacecraft receivers. Two case studies show that the location of active aurora, presumed connected with the AKR sources, controls whether or not the ground station detects the AKR, or which of several ground stations detects it most strongly. These investigations strengthen the hypothesis that through some mechanism, sources of outgoing AKR detected by distant satellites occasionally generate signals detectable as whistler mode waves at low altitude or right‐hand polarized signals at ground level.