Transient ion beamlet injections into spatially separated PSBL flux tubes observed by Cluster‐CIS

Abstract

[1] Ion measurements from Cluster-CIS were used to characterize and interpret the signatures of PSBL energydispersed ions and their fine structure. On 14 February 2001, several ion injections were encountered by SC 1 and SC 3, separated by $530 km, during an outbound orbit at 4.5 R E . Both satellites recorded the same ion structures. The energy dispersion of each ion structure was dominated by the timeof-flight effect (TDIS). In addition, we show evidence for spatial properties of the ion injections: (1) SC 1 and SC 3 encountered the same ion structures with a time delay of $30 s, which indicates their spatial extent. (2) The peak energy of each injection increased with increasing latitude. We propose a scenario in which both temporal and spatial effects are incorporated: Ion beamlets are impulsively and recurrently injected from separated regions distributed along the tail current sheet (ranging from X $70 to 110 R E ) into latitudinally narrow ($600 km to 1800 km) and convecting (at $10 km/s) flux tubes of the PSBL. Beamlets injected closer to the X line gain higher energies as a result of the intrinsic dispersion effect.

Energy-dispersed ions in the plasma sheet boundary layer and associated phenomena: Ion heating, electron acceleration, Alfvén waves, broadband waves, perpendicular electric field spikes, and auroral emissions

“…5.7 Association with poleward arcs of double oval As previously reported, both events occurred during a double auroral oval and the footprints of the beamlets mapped into the vicinity of the poleward arcs (Keiling et al, 2004b). The conjugacy of ion beamlets and auroral activity begs the question whether the ions were responsible for the auroral emissions.…”

“…Since we argued above that the edges of ion beamlets were associated with the heating of the ion conics, one might expect that the ion conics would be displaced from the edges due to this E×B drift which however was not observed. In Keiling et al (2004b) it was concluded that the edges of ion beamlets on 14 February 2001 were caused by a distant tail source which itself convected with the E×B drift, thus creating a broad energy range on the same field line (see also Lennartsson et al, 2001). Therefore, the E×B drift of the source regions of both magnetotail beamlets and ion conics -both located on the same flux tubescould explain why no separation of beamlets and ion conics occurred.…”

“…These steps separate individual beamlets from one another. In Keiling et al (2004b), it was determined using multiple spacecraft measurements that the steps were caused by crossing spatial boundaries of flux tubes carrying the magnetotail ion beamlets (as opposed to a sudden appearance of a beamlet). The sharp boundaries have spatial scales of <60 km since the ion fluxes changed abruptly from one sample to the next (4-s time resolution of the ion instrument) and the relative motion of spacecraft and ambient plasma was about 15 km/s.…”

“…1a). Although the energetic ion signatures in the E-t spectrogram appear at first glance to be very different (best seen by comparing the dispersion slopes of the ions) from the inbound event (Southern Hemisphere), we proposed that in fact the same injection scenario operated during both inbound and outbound crossings creating the dispersion signatures (Keiling et al, 2004b). Consequently, one might expect that the impact of the dispersed ions on their plasma environment should be the same for both events, in spite of their differences in appearance in the E-t spectrograms, and we will show evidence for this.…”

Relating field-aligned beams to inverted-V structures and visible auroras

“…The pitch-angle spectrograms of the ions in the PSBL (bottom three panels) show that the ions are field-aligned, and all measurements come from the pitch-angle bins closest to the magnetic field direction. Important features on this day include time-dispersed ion injections observed in all ion species beginning around 00:44 UT, previously studied by Keiling et al (2004), who showed that the injection included four to five "beamlets" separated by ∼ 100 s. Injections of the lower-energy ions of ∼ 1 keV occurred in coincidence with these beamlets. As the spacecraft entered into the inner boundary of the PSBL (after 00:55 UT), higher-energy ions and inverted-V structures were observed; see Cui et al (2014) for further discussion of these inverted-V events.…”