Dartmouth Events

Abstract: Different types of radar echoes are observed associated with aurora, including some which have been interpreted as signatures of cavitating Langmuir turbulence (cavitons). Akbari et al. [2013] observe two instances of correlation between such radar echoes and naturally occurring radio emissions called medium frequency burst (MFB) which occur at substorm onsets. Radio data from Toolik Lake Observatory (68° 38’ N, 149° 36’ W, 68.51° magnetic latitude) and radar data from Poker Flat Incoherent Scatter Radar (PFISR) have been applied to investigate occurrence of radar echoes and correlation with MFB using many events. 25 of 131 identified MFB events occurred within 15 minutes of a detection of a radar echo. In a control set with similar local time and seasonal distribution, 6 of 116 intervals were similarly associated with radar echoes. The difference is significant at the 10^-4 level, suggesting that radar echoes are more probable during substorm onset times identified using MFB as a proxy. However, only four of the observed radar echoes associated with one MFB event showed specific characteristics consistent with cavitons, suggesting cavitons are relatively rare. The MFB in that event and others associated with radar echoes did not come from the direction of the radar, however, and this observation as well as the relatively low number of correlated events means that due to the large difference in the spatial volumes sensed by the two techniques, this study elucidates the occurrence rate of radar echoes under different conditions but does not definitively answer the question of a connection between cavitons and MFB emissions.