Solitary Potential Structures Observed on the Cluster Spacecraft: Correlated Wave and Particle Measurements

Each of the four Cluster spacecraft contains a wideband (WBD) receiver for detecting plasma waves with high time resolution in the frequency range of 25 Hz to 580 kHz. The WBD waveform data are directly downlinked to a DSN ground station at 220 kbits/sec. In this study we examine the WBD data for evidence of solitary potential structures, or phase-space holes, that propagate along the earth's magnetic field. The potential structures are identified in the WBD waveform data by a characteristic bipolar or unipolar pulse that occurs over short time periods, characteristically a few hundred microseconds to one millisecond. In the frequency domain these structures comprise at least the high frequency part of the Broadband Electrostatic Noise (BEN) that has been observed by numerous spacecraft in the past. We analyze wave measurements that are obtained simultaneously on up to four Cluster spacecraft in the magnetosphere and magnetosheath to better understand the propagation and spatial characteristics of the solitary potential structures. Particle (PEACE and CIS) and wave-particle correlator (DWP) data are examined, sometimes during periods of spacecraft potential control by ASPOC, for evidence of wave-particle interactions leading to local generation of the structures by particles and/or local heating and acceleration of particles by these structures. One example will be shown where counter-streaming electron beams of a few hundred eV are observed coincident with the solitary potential structures for a period of one minute when the spacecraft are in the southern auroral zone. DC electric (EFW) and magnetic field (FGM) data are analyzed in conjunction with our findings.