Magnetic and electric field waves in slow shocks of the distant geomagnetic tail: ISEE 3 observations

Abstract

During the first pass through the distant geomagnetic tail by ISEE 3 the slow shocks encountered on February 2 and 11, 1983, provide particularly clear examples of the magnetic field and plasma wave properties of the shock transition. The magnetic ramp contains transverse polarized magnetic field oscillations with frequencies just below the ion cyclotron frequency and amplitudes of 2‐4 nT. These waves are plausibly generated by the electromagnetic ion/ion cyclotron instability predicted by Winske and Omidi (1990). The electric field plasma waves within the shock ramp exhibit two spectral peaks. A midfrequency emission occurs near the ion plasma frequency and electron cyclotron frequency but well below the maximum Doppler shift frequency for electrostatic waves. The midfrequency waves extend into the upstream region where the spectral peak occurs at a slightly higher frequency. A new high‐frequency emission with frequencies between the maximum Doppler shift frequency and the electron plasma frequency occurs throughout the downstream region. This emission disappears at the start of the magnetic ramp and is replaced upstream by electron plasma oscillations. The high‐frequency emissions are clearly polarized parallel to the magnetic field. The polarization of the midfrequency waves is less certain; both parallel and a fairly broad angular distribution about the parallel electric fields are consistent with the measurements.