Cluster Wideband Observations of Low Frequency Bursts

On many occasions the Cluster Wideband (WBD) experiments, when operating in the 77 kHz mode, have detected bursts of emissions with primarily vertical structure extending from the upper frequency limits down to a few tens of kHz. Simultaneous observations from the Geotail Plasma Wave Instrument and the Wind Waves experiment show that those emissions are low frequency bursts. The high-frequency resolution and high-time resolution Cluster WBD measurements show that for the majority of the observations, the fine structure is quite similar to that observed for the higher frequency Auroral Kilometric Radiation. However, for some observations, the fine structure resembled that for escaping continuum and kilometric continuum radiation. The different implications for the sources and propaagation paths of the emissions will be discussed.