Abstract. Using four-point magnetic field measurements by the Cluster spacecraft, we statistically analyze the magnetic field and electric current configurations during rapid crossings of the current sheet observed in July-October 2001 at geocentric distances of 19 R E . The database includes 78 crossings, specially selected to apply multi-point data analysis techniques to calculate vector derivatives. Observed bipolar variations of j z , often with |j z |>j y , indicate that the electric currents follow kinks of the current sheet. The current density varies between 5-25 nA/m 2 . The half-thickness of the current sheet during flapping varies over a wide range, from 1 to 20 ion thermal gyroradii (L cp , calculated from average temperature and lobe magnetic field for each crossing). We found no relationship between the tilt angle of the current sheet normal and the half-thickness. In 68 cases the magnetic field curvature vector has a positive (earthward) X-component. Ten cases with a negative (tailward) curvature, associated with reconnection, were detected within 0
[1] In this paper we use the statistics of 70 crossings by the Cluster mission to study and compare properties of thin current sheets observed at the dawn and dusk flanks of the Earth magnetotail. Special attention is devoted to the current sheet embedding: we define the degree of the current sheet embedding as b e = B ext /B 0 (B 0 and B ext are magnetic field magnitudes at the thin current sheet boundary and in the lobes). We determine the current density by curlometer technique and calculate the current sheet thickness. We demonstrate that the current sheets at the dawn flank have larger b e , smaller magnitude of the current density and larger relative thicknesses in Larmor radii than the current sheets at the dusk flank. Protons in thin current sheets are divided into two populations (the current-carrying particles and the background) and the temperatures of these populations have been estimated. The distribution of the proton temperatureT p inside typical current sheet is approximated asT p ≈ T p (1 − a T (B x /B ext ) 2 ), where T p is theT p value in the central region of the current sheet. The average value ha T i ≈ 0.8. The proton current density (flow velocity in Y) is positive at the dusk flank and negative at the dawn flank, while the electron current density is positive at both flanks. This difference of the proton current density at two flanks is explained by the E × B drift due to the presence of the earthward electrostatic field E x . We develop a simple model of the earthward electrostatic field to incorporate the influence of the embedding and the dawn-dusk magnetic field component.
[1] With Cluster observations in the magnetotail we study dynamics of plasma sheet thinning and stretching during 39 intervals associated with substorm growth phases. The cross-tail current density and normal magnetic field generally scale as B n $ T p N p 1/2 /J 0 , but with frequent transient variations. Typical pre-onset values are B z $ 1-2 nT, J 0 $ 4-8 nA/m 2 , thickness (Harris estimate) >3000 km. A current density increase in each particular event is not accompanied with a corresponding number density increase. About 30% of the events are characterized by a large (>5 nT) field component parallel to the current (in most of cases equal to B y ), implying adiabatic particle dynamics even with small B z . Most local onsets, associated with the ends of thin sheet intervals, were accompanied with tailward plasma flows. In some cases embedded current sheet structure was detected and, therefore, estimation of thickness requires caution.
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