Observations of auroral medium frequency bursts

Auroral medium frequency (MF) bursts are broadband impulsive radio emissions observed at ground level during the breakup phase of auroral substorms. Measurements made in northern Canada during 1995-1996 show the seasonal and local time dependencies of MF burst emissions, provide case-study evidence for a null in the MF burst spectrum near twice the ionospheric electron gyrofrequency, and establish a correlation between MF burst and impulsive auroral hiss. High time resolution measurements reveal that MF bursts occur in 100-300 mu s wave packets which sometimes appear periodic having a period close to the ionsopheric proton gyroperiod. The timescales of the MF burst wave packets are comparable to those of whistler solitary waves recently observed with the FAST satellite.