Geomagnetic signatures of current wedge produced by fast flows in a plasma sheet

Abstract

[1] This paper uses the plasma data from Cluster and TC-1 and geomagnetic data to study the geomagnetic signatures of the current wedge produced by fast-flow braking in the plasma sheet. The three fast flows studied here occurred in a very quiet background and were accompanied by no (or weak) particle injections, thus avoiding the influences from other disturbances. All the geomagnetic signatures of a substorm current wedge can be found in the geomagnetic signatures of a current system produced by the braking of fast flows, indicating that the fast flows can produce a complete current wedge which contains postmidnight downward and premidnight upward field-aligned currents, as well as a westward electrojet. The Pi2 precursors exist not only at high latitudes but also at midlatitudes. The starting times of midlatitude Pi2 precursors can be identified more precisely than those of high-latitude Pi2 precursors, providing a possible method to determine the starting time of fast flows in their source regions. The AL drop that a bursty bulk flow produces is proportional to its velocity and duration. In three cases, the AL drops are <100 nT. Because the AE increase of a typical substorm is >200 nT, whether a substorm can be triggered depends mainly on the conditions of the braking regions before fast flows. The observations of solar wind before the three fast flows suggest that it is difficult for the fast flows to trigger a substorm when the interplanetary magnetic field B z of solar wind is weakly southward.Citation: Cao, J. -B., et al. (2010), Geomagnetic signatures of current wedge produced by fast flows in a plasma sheet,

M–I coupling across the auroral oval at dusk and midnight: repetitive substorm activity driven by interplanetary coronal mass ejections (CMEs)

“…The streamer signature is observed within the field of view of these stations (spanning the latitude range 71 to 63 • MLAT) during a 10 min-long interval (15:10-15:20 UT). The properties of the streamer deflections, i.e., their amplitude and temporal scale, as well as the propagation pattern (equatorward from PBIs in the highlatitude auroral branch), are all consistent with an interpretation in terms of plasma sheet flow bursts (BBFs) (see Cao et al, 2010, their Fig. 4).…”

On the current sheets surrounding dipolarizing flux bundles in the magnetotail: The case for wedgelets

“…Recent support for the tight DFB‐SCW correlation comes from the strong coincidence between dipolarizations and ground midlatitude Pi2 pulsations observed by Cao et al . [], Lyons et al . [], and Nishimura et al .…”

Poloidal ULF wave observed in the plasmasphere boundary layer

“…The terms “poloidal” and “toroidal” modes are used for standing Alfvén waves with magnetic field (and plasma bulk motion) oscillations in the radial and azimuthal directions (or the corresponding azimuthal and radial electric field), respectively. For the poloidal mode in the Pc4 (6.7–22 mHz) and Pc5 (1.7–6.7 mHz) bands studied in this paper, several generation mechanisms have been suggested after decades of study, including drift resonance [ Southwood , ], drift‐bounce resonance [ Southwood , ; Hughes et al ., ], impact of interplanetary shocks [ Zong et al ., ; Sarris et al ., ], Alfvén oscillations with high azimuthal numbers [ Kozlov et al ., ; Leonovich et al ., ], and activity in the magnetotail [ Cao et al ., , ].…”