Abstract
Abstract. We investigate strongly tilted (in the y–z GSM plane) current sheets (CSs) in the Earth magnetotail using data from the Cluster mission. We analyze 29 CS crossings observed in 2001–2004. The characteristic current density, magnetic field at the CS boundary and the CS thickness of strongly tilted CSs are similar to those reported previously for horizontal (not tilted) CSs. We confirm that strongly tilted CSs are generally characterized by a rather large northward component of the magnetic field. The field-aligned current in strongly tilted CSs is on average two times larger than the transverse current. The proton adiabaticity parameter, κp, is larger than 0.5 in 85% of strongly tilted CSs due to the large northward magnetic field. Thus, the proton dynamics is stochastic for 18 current sheets with 0.5 < κp < 3 and protons are magnetized for 6 sheets with κp > 3, whereas electrons are magnetized for all observed current sheets. Strongly tilted CSs provide a unique opportunity to measure the electric field component perpendicular to the CS plane. We find that most of the electric field perpendicular to the CS plane is due to the decoupling of electron and ion motions (plasma polarization). For 27 CSs we determine profiles of the electrostatic potential, which is due to the plasma polarization. Drops in the potential between the neutral plane and the CS boundary are within the range of 200 V to 12 kV, while maximal values of the electric field are within the range of 0.2 mV m−1 to 8 mV m−1. For 16 CSs the observed potentials are in accordance with Ohm's law, if the electron current density is assumed to be comparable to the total current density. In 15 of these CSs the profile of the polarization potential is approximately symmetric with respect to the neutral plane and has minimum therein.
Highlights
The current sheet (CS) is a fundamental element of the Earth magnetotail (Ness, 1965)
We have studied properties of strongly tilted CSs using a data set of 29 CS crossings
Our conclusions are summarized below: 1. Strongly tilted CSs are in many respects similar to horizontal CSs: the current density is generally smaller than ∼ 15 nA m−2, the magnetic field B0 is on average ∼ 18 nT and the CS thickness is generally smaller than 10 proton gyroradii or 3000 km
Summary
The current sheet (CS) is a fundamental element of the Earth magnetotail (Ness, 1965). In the present paper we study the structure of tilted CSs with the normal vector n directed almost along the y axis, i.e., the angle γ of the CS inclination is smaller than 30◦ (see Fig. 1) In these strongly tilted CSs, the current flows almost along the z axis. In tilted CSs, By Bz (Petrukovich et al, 2006), there is significant field-aligned current near the neutral plane (Shen et al, 2008) In this respect strongly titled CSs are similar to horizontal CSs with substantial By component (Rong et al, 2012). In horizontal CSs the electric field due to the decoupling of electron and ion motions (plasma polarization) is along the z axis (Zelenyi et al, 2004; Schindler et al, 2012) This field has not been observed, since Cluster measures electric field components in the spin plane (approximately XY GSE).
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