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 &mgr;s wave packets which sometimes appear periodic having a period close to the ionospheric proton gyroperiod. The timescales of the MF burst wave packets are comparable to those of whistler solitary waves recently observed with the FAST satellite. ¿ 1997 American Geophysical Union