Downward current electron beam observed by Cluster and FAST

Abstract

[1] We report observations from a conjunction of FAST and Cluster during an interval of downward current at an MLT of 3-4 h on field lines mapping to the PSBL. Both spacecraft see upgoing electrons with an energy of a few hundred eV, suggesting substantial acceleration has occurred below FAST's altitude of 3200 km. At Cluster, isolated bursts of electrons are seen, and modeling indicates that the current mapped from the ionosphere exists as a collection of current filaments at Cluster (4-5 R E ). The current filaments are aligned with the background magnetic field and have a perpendicular scale at Cluster of about 100 km (which maps to 10-20 km in the ionosphere), and is similar to the mapped width observed by FAST. The electron beams are quasi-steady during a Cluster spacecraft transit time of 1 min. The field aligned current densities at FAST and Cluster are of the order of a few mAms À2 and 0.05 mAm À2 , respectively, and j/B is conserved along a current filament.

Sources of electron pitch angle anisotropy in the magnetotail plasma sheet

“…This could simply be a result of less precise magnetic field mapping under more disturbed conditions [e.g., Kubyshkina et al , ] masking and distorting the pattern; because of the presence of additional current systems under southward IMF [cf. Wright et al , ] that do not contribute significantly under northward IMF, or indeed a combination of the two. The sense of the dawn‐dusk asymmetry in occurrence is the same as other measures of magnetotail dynamics, for example, the thickness of the current sheet [ Runov et al , , ] and the duskward offset of the magnetotail X line [ Imber et al , ].…”

Quasi-parallel electron beams and their possible application in inferring the auroral arc's root in the magnetosphere

“…Eventually, the electron beams appear on magnetosphere satellite measurements as collimated beams with finite beam width (∼ 10-15 • in the nightside inner magnetosphere as surveyed by Abel et al, 2002b) along directions both parallel and antiparallel to the ambient magnetic field. Such bidirectional, collimated electron beams were previously reported on the basis of data from magnetospheric satellites such as ATS-6 (Lin et al, 1979), AMPTE/CCE (Klumpar et al, 1988;Klumpar;1993), CRRES (Abel et al, 2002a, b), and Cluster (Marklund et al, 2004;Wright et al, 2008). The nomenclature used to describe such phenomena differs from author to author, but in this paper we will use the terminology "quasiparallel electron beam" (QPEB).…”

“…Correspondingly, QPEBs were also observed in various regions of the magnetosphere, e.g., in the inner magnetosphere and the central plasma sheet (CPS) (Klumpar et al, 1988;Klumpar, 1993;Abel et al, 2002a, b), in the highlatitude PSBL (Marklund et al, 2004;Wright et al, 2008), or even in the polar cap (Teste et al, 2007). Therefore, it is important to first clarify the region of observation and interest in this study: (1) we are only interested in the premidnight sector, (2) we are only interested in the equatorwardmost, mesoscale (width 1 km) arc close to the equatorward border of the auroral oval, and (3) we are only interested in the inner CPS (L < 12) region.…”

Introduction to special section on Double Star‐Cluster Coordinated Studies on Magnetospheric Dynamic Processes

“…The field aligned current filaments with outflow electrons from the ionosphere have been observed by both FAST and Cluster spacecraft. Upgoing electrons with energy of a few hundred eV, suggesting substantial electron acceleration occurred below FAST's altitude of 3200 km [ Wright et al , 2008]. The current filaments have a perpendicular scale of a few hundred kilometers as observed by Cluster tetrahedral (which maps to a few tens of kilometers at FAST).…”