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

Abstract

Ion measurements from Cluster-CIS were used to characterize and interpret the signatures of PSBL energy-dispersed 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 time-of-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.