Observations of low frequency terrestrial type iii bursts by geotail and wind and their association with isolated geomagnetic disturbances detected by ground and space-borne instruments

摘要

The low frequency (LF) terrestrial type III radio burst is a plasma wave emission that typically below 60 to 100 kHz has a smooth time profile and a negative frequency drift. After reviewing past observations, we will examine two LF burst events observed by both the GEOTAIL Plasma Wave Instrument and the WIND WAVES experiment while both spacecraft were in the solar wind and upstream from the Earth's bow shock but at widely separated locations. In both cases enhanced auroral ilometric radiation (AKR) was observed simultaneously with the LF burst by the spacecraft with the least obstructed view of the nightside magnetosphere. The CANOPUS ground magnetometer data and magnetorams from the National Geophysical Data Center (NGDC) show that the LF burst events are well correlated with the expansive phase onsets of intense isolated substorms detected by observing stations near local midnight. In the magnetometer data for GOES 8 we have found enhanced field aligned currents and magnetic field dipolarization observed simultaneously with a strong LF burst event. The recent launch of POLAR has allowed us to detect the AKR very near the source region. Details of the wave observations from WIND, GEOTAIL, and POLAR along with the ground and space magnetometer data indicate an intimate relationship between AKR, geomagnetic substorms, and LF bursts. We suggest that the dynamics of the substorms may be responsible for some of the observed time dispersion in the LF bursts.