Relationship between auroral substorms and the occurrence of terrestrial kilometric radiation

We have examined the correlation between magnetospheric substorms as inferred from the AE(11) index and the occurrence of terrestrial kilometric radiation (TKR) as observed by the Goddard radio astronomy experiment on board the Imp 6 spacecraft. In general, we find that AE and TKR are well correlated when observations are made from above the 1500–0300 hour local time zone and are rather poorly correlated over the 0300–1500 hour zone. High‐resolution dynamic spectra obtained during periods of isolated substorms indicate that low‐intensity high‐frequency TKR commences at about the same time as the substorm growth phase. The substorm expansion phase corresponds to a rapid intensification and bandwidth increase of TKR. When these new observations are combined with our previous results, they imply that many TKR events begin at low altitudes and high frequencies (∼400–500 kHz) and spread to higher altitudes and lower frequencies as the substorm expands.