Measurements from the Lepedea plasma instruments and the flux gate magnetometers on ISEE 1 and 2 are used to examine the nature of the hydromagnetic waves associated with the various classes of ions backstreaming from the earth's bow shock. The reflected ions, which are confined to a narrow energy and angular range, are accompanied by small amplitude (≲½γ peak to peak) left‐handed waves at frequencies close to 1 Hz in the spacecraft frame. Diffuse backstreaming particles with a broad energy spectrum are associated with low frequency (∼ 30‐s period) large amplitude (∼5γ peak to peak) waves. Intermediate particles are associated with a mixture of these two wave types. Often the waves associated with the diffuse beams steepen as if they were mini shocks. The leading edge (trailing edge in the spacecraft frame) frequently appears to break up into a whistler mode wave packet. These discrete wave packets are right‐hand polarized and have frequencies from below the proton gyrofrequency to well above it in the plasma frame and are blown back towards the earth by the solar wind.

A traveling compression region (TCR) is a several‐minute long compression of the lobe magnetic field produced by a plasmoid as it moves down the tail. They are generally followed by a longer interval of southward tilting magnetic fields. This study reports the first comprehensive survey of TCRs in the distant magnetotail. A total of 116 TCRs were identified in the ISEE 3 magnetic field observations. Of this population, 37 TCRs were observed to be separated by 30 min or more from any other TCR and are termed “isolated” events. “Paired” events are defined as two TCRs separated by less than 30 min. There were 36 such TCRs corresponding to 18 paired events. “Multiple” events were also observed in which more than two TCRs occurred in a series without a gap between TCRs of more than 30 min. The 11 multiple events identified in this study had an average of about four traveling compression regions each for a total of 43 TCRs. The mean amplitude, ΔB/B, and duration, ΔT, for all TCRs were found to be 7.6% and 158 s, respectively. TCRs occurring as isolated events were the largest (ΔB/B = 8.8% and ΔT = 218 s) and those associated with multiple events were the smallest (ΔB/B = 5.6% and ΔT = 84 s). The mean duration of the period of southward tilting Bz following isolated TCRs was 12.3 min. This time interval was found to be quite similar to the average spacing between TCRs in paired and multiple events, 11.2 and 10.2 min, respectively. TCR amplitude and duration were found to be independent of location within the tail lobes suggesting that the plasmoids which cause the TCRs maintain approximately constant volume and shape as they move down the tail. Mean plasmoid dimensions estimated from TCR duration and amplitude under the assumption of a quasi‐rigid magnetopause are 35 RE (length) × 15 RE (width) × 15 RE (height). Utilizing auroral kilometric radiation, the AL index, Pi 2 pulsations at two ground stations, and energetic particle data from three geosynchronous spacecraft, it is found that over 91% of the TCR events identified in this study followed substorm onsets or intensifications. The number of TCR events identified in this study are consistent with their release in association with a new substorm onset every 4‐6 hrs. The results of this study strongly suggest that the release of plasmoids down the tail near the time of expansion phase onset is an integral step in the substorm process and an important element in the substorm energy budget.

Observations obtained upstream of the earth’s bow shock with the LASL/MPI plasma instruments and the UCLA magnetometers on ISEE‐1 and 2 have revealed a striking relationship between the presence of low‐frequency fluctuations in solar wind density and field strength and the different types of distribution functions of upstream ions. Waves are absent when the ions have the beamlike distribution of the “reflected” ions. Large‐amplitude waves are present only in conjunction with the “diffuse” ions, which are characterized by flat energy spectra and broad angular distributions. The waves are largely compressive, showing very good correlation between oscillations in magnetic field strength and plasma density.

We have studied the structural elements, including shock ramps and precursor wave trains, of a series of oblique 1ow-Mach number terrestrial bow shocks. We used magnetic field data from the dual ISEE 1 and 2 spacecraft to determine the scale lengths of various elements of shock structure as well as wavelengths and wave polarizations. Bow shock structure under these conditions is essentially that of a large-amplitude damped whistler mode wave which extends upstream in the form of a precursor wave train. Shock thicknesses, which are determined by the dispersive properties of the ambient plasma, are too broad to support current-driven electrostatic waves, ruling out such turbulence as the source of dissipation in these shocks. Dissipative processes are reflected in the damping of the precursors, and dissipative scale lengths are ~200-800 km (several times greater than shock thicknesses). Precursor damping is not related to shock normal angle or Mach number, but is correlated with Te/T •. The source of the dissipation in the shocks does not appear to be wave-wave decay of the whistlers, for which no evidence is found. We cannot rule out the possibility of contributions to the dissipation from ion acoustic and/or lower-hybrid mode turbulence, but interaction of the whistler itself with upstream electrons offers a simpler and more self-consistent explanation for the observed wave train damping. (inward) motion. :[The sign of the wave velocity indicates the polarization of the waves as observed in the spacecraft frame: +(-) corresponding to right-handed (left-handed) waves.õSpacecraft separation too small to allow accurate measurements.

Ion spectrums and magnetograms obtained simultaneously when the Vela 3A satellite crossed the earth's bow shock have been correlated. An intermediate form of ion spectrum, representing neither solar wind nor magnetosheath, but characterized by an irregular envelope and occasional large flux peaks, is found to correspond to the appearance of large‐amplitude (10‐25 γ), irregular magnetic oscillations of 4‐to 30‐sec period. The large spectral flux peaks of the shock seem to result from localized transient accelerations and decelerations of the bulk of the solar wind protons. Smaller amplitude (<5 γ), longer period (20‐60 seconds), generally more regular magnetic oscillations are seen in the solar wind outside the shock where the direction of flow of ion flux peaks is found to oscillate in close correlation with magnetic waves.