Nonlocal plasma turbulence associated with interplanetary shocks

Abstract

The plasma wave instrument on ISEE 3 has detected regions of plasma turbulence that extend several tenths of an astronomical unit upstream or downstream of inteplanetary shocks. The plasma waves fall into four categories. Highly impulsive 1‐ 10‐kHz electric field bursts were found hours upstream of quasi‐parallel interplanetary shocks. On occasion their average and peak amplitudes increased monotonically until the shock crossing, at which time they were suppressed. A lower frequency electric field (0.1–1 kHz) component was enhanced at nearly all shocks and persisted downstream. Broadband low‐frequency (typically <178 Hz) magnetic fluctuations increased at, and persisted hours downstream of, every interplanetary shock in our sample. A smooth high‐frequency continuum, near and above the local electron plasma frequency, was enhanced at, and persisted well downstream of, every interplanetary shock we studied. Impulsive electron plasma wave bursts were occasionally found near the shocks. The shock‐associated plasma waves we found to extend over large spatial scales are similar to those found previously in local studies of interplanetary shocks. While no single interplanetary shock showed every effect, the ensemble of shocks contained at least one example of each type of plasma wave found upstream of the earth's bow shock. The 1‐ to 10‐kHz spectra upstream of interplanetary shocks and the earth's bow shock are similar. The low‐frequency electric and magnetic fluctuations downstream of interplanetary shocks and the bow shock have similar spectra. They seem to be ubiquitous features of flowing plasmas made turbulent by a shock.

Waves and Instabilities in Collisionless Shocks

“…If the broadband component is due to whistler mode waves then the waves could either be generated in the transition region, or they could be generated locally. For interplanetary shocks the intensity of the broadband magnetic noise is sometimes observed to decrease exponentially with increasing distance from the shock Kennel et al, 1982]. These observations suggest that the noise is generated in the transition region and slowly damps as it propagates into the downstream region.…”

“…This difference is illustrated in Figure 5 which shows the electric and magnetic field spectrums for a series of interplanetary shocks detected by the ISEE-3 spacecraft at 1 AU. The electric and magnetic field turbulence of these shocks has been previously discussed by Kennel et al [1982]. By comparing these spectrums with the IMP-6 spectrums in Figure 2, it can be seen that the electric field intensities of the interplanetary shocks are about two to three orders of magnitude lower than for the earth's bow shock.…”

“…Plasma wave turbulence similar to that observed at planetary bow shocks has been reported in association with interplanetary shocks by a number of investigators, including Scarf et al [1974], Neubauer et al [1977], Scarf [1978, Gurnett et al [1979], and Kennel et al [1982]. Interplanetary shocks can be produced either by flares at the sun, or by co-rotating high speed streams [Hundhausen, 1972].…”

“…by Coroniti et al [1982], This disagreement could either indicate that an additional electrostatic component is present, or that the whistler mode waves are propagating at a large angle to the magnetic field. At large wave normal angles, near the resonance cone, the whistler mode becomes quasielectrostatic, which would tend to reduce the CBL/E^ ratio.…”

An increase in Pc1 wave activity prior to magnetic sudden impulses

“…The best known example of such regions is plasma wave turbulence in front of the Earth's bow shock [e.g., Russell and Hoppe, 1983; Le and Russell, 1994; Blanco-Cano et al, 1999]. Interplanetary blast shocks generated by solar flares display similar structures [Kennel et al, 1982[Kennel et al, , 1984Lee, 1983]. Therefore the magnetosphere is exposed to the interplanetary upstream wave turbulence some time before the SI.…”