Abstract. Thirty rapid crossings of the magnetotail current sheet by the Cluster spacecraft during July-October 2001 at a geocentric distance of 19 R E are examined in detail to address the structure of the current sheet. We use four-point magnetic field measurements to estimate electric current density; the current sheet spatial scale is estimated by integration of the translation velocity calculated from the magnetic field temporal and spatial derivatives. The local normalrelated coordinate system for each case is defined by the combining Minimum Variance Analysis (MVA) and the curlometer technique. Numerical parameters characterizing the plasma sheet conditions for these crossings are provided to facilitate future comparisons with theoretical models. Three types of current sheet distributions are distinguished: centerpeaked (type I), bifurcated (type II) and asymmetric (type III) sheets. Comparison to plasma parameter distributions show that practically all cases display non-Harris-type behavior, i.e. interior current peaks are embedded into a thicker plasma sheet. The asymmetric sheets with an off-equatorial current density peak most likely have a transient nature. The ion contribution to the electric current rarely agrees with the current computed using the curlometer technique, indicating that either the electron contribution to the current is strong and variable, or the current density is spatially or temporally structured.

[1] Observations of three closely-spaced THEMIS spacecraft at 9 -11 Re near midnight and close to the neutral sheet are used to investigate a sharp injection/ dipolarization front (SDF) propagating inward in the flow-braking region. This SDF was a very thin current sheet along the North-South direction embedded within an Earthward-propagating flow burst. A short-lived depression of the total magnetic field (down to 1 nT), devoid of wave activity and intense particle fluxes, stays ahead of the SDF. Clear finite proton gyroradius effects, which help visualize the geometry and sub-gyroscale of the SDF, are seen centered at the thin current sheet. The SDF nearly coincides with the narrow interface between plasmas of different densities and temperatures. At that interface, we observed strong (40 -60 mV/m peak) Efield bursts of the lower-hybrid time scale that are confined to a localized region of density depletions. This sharp dipolarization/injection front propagating in the flow-braking region appears to be a complicated kineticscale plasma structure that combines a number of smallscale elements (Bz drops, thin current sheets, LH cavities, injection fronts) previously discussed as separate objects.Citation: Sergeev, V

Almost 40 years ago the concept of the substorm current wedge was developed to explain the magnetic signatures observed on the ground and in geosynchronous orbit during substorm expansion. In the ensuing decades new observations, including radar and lowaltitude spacecraft, MHD simulations, and theoretical considerations have tremendously advanced our understanding of this system. The AMPTE/IRM, THEMIS and Cluster missions have added considerable observational knowledge, especially on the important role of fast flows in producing the stresses that generate the substorm current wedge. Recent detailed, multi-spacecraft, multi-instrument observations both in the magnetosphere and in the ionosphere have brought a wealth of new information about the details of the temporal evolution and structure of the current system. While the large-scale picture remains valid, the new

[1] A multipoint analysis of conjugate magnetospheric and ionospheric flow vortices during the formation of the substorm current wedge (SCW) on 19 February 2008 is presented. During the substorm, four Time History of Events and Macroscale Interactions during Substorms (THEMIS) spacecraft were located close to the neutral sheet in the premidnight region between 9 and 12 R E geocentric distance, of which three closely ($1-2 R E ) clustered at $23 MLT and one was farther west at $21 MLT. The closely clustered spacecraft were engulfed by a counterclockwise plasma flow vortex, while the single spacecraft recorded a clockwise plasma flow vortex. Simultaneously, a pair of conjugate flow vortices with clockwise and counterclockwise rotation appeared in the ionosphere, as inferred from equivalent ionospheric currents. The counterclockwise space vortex, which corresponded to a downward field-aligned current, was at least 1-2 R E in diameter and had rotational flow speeds of up to 900 km/s. Current density estimates associated with the formation of the space vortex in the first 30 s yielded 2.8 nA/m 2 (14 mA/m 2 mapped to the ionosphere), or a total current of 1.1 Â 10 5 A. Model calculations based on midlatitude ground magnetometer data show a gradual increase of the field-aligned current, with 1-2 Â 10 5 A within the first minute and a peak value of 7 Â 10 5 A after 10 min, associated with the SCW, and a matching meridian of the downward current of the SCW and the downward current (counterclockwise) space vortex. The combined ground and space observations, together with the model results, present a scenario in which the space vortices generated the field-aligned current of the SCW at the beginning of the substorm expansion phase and coupled to the ionosphere, causing the ionospheric vortices.