ISEE 3 observations of traveling compression regions in the Earth's magnetotail

Abstract

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.

Energy conversion regions as observed by Cluster in the plasma sheet

“…The plasma sheet is known to play a central role for the energy budget of the Earth's magnetosphere [e.g., Lyons, 2000;Koskinen and Tanskanen, 2002;Pulkkinen et al, 2003]. During substorms, the amount of energy dissipated in the plasma sheet (in the form of plasmoid ejection and ion heating) is comparable to the ring current dissipation, auroral Joule heating and charged particle precipitation into the ionosphere [Ieda et al, 1998;Slavin et al, 1993]. Since the plasma sheet maps to the nightside auroral ionosphere, various regions in the plasma sheet have been suggested to host auroral generators, for example, the low-latitude boundary layer and the plasma sheet boundary layer (PSBL).…”

Dual spacecraft observations of lobe magnetic field perturbations before, during and after plasmoid release

“…Traveling compression regions are several minute long enhancements of the magnetic field in the lobes of the tail during which there is a north-then-south variation in B z relative to a mean baseline (Slavin et al, 1993). The greater north-south dimensions of the plasmoid relative to the plasma sheet result in the lobe field lines being compressed and draped about the plasmoid as it moves down the tail.…”

High-speed flowing plasmas in the Earth’s plasma sheet

“…In the meantime, earthward flowing plasmoids or magnetic structures have also been observed [41,42]. Plasmoids are observed singly or in groups [41,43]. Frequently, the observed flux ropes are believed to be evidence of a near-Earth multi-X line reconnection process that can produce more than one plasmoid in the plasma sheet.…”