Thin current sheets in the Jovian magnetotail

Abstract In this paper we investigate the fine structure of the current sheet located at the dawn side (and the central region) of the Jovian magnetotail (magnetodisk). We consider observational data collected by Galileo spacecraft (our dataset includes 226 current sheet crossings). Measurements of spectra of electric field fluctuations allow us to estimate the electron density. The plasma temperature is estimated from the vertical stress balance in the current sheet. To determine the vertical structure of the current sheet we use magnetic field measurements and the model of the neutral plane vertical motion. The current sheet vertical structure includes two spatial scales: the thin current sheet with the thickness around two Larmor radii of thermal sulfur ions is embedded into the thick current sheet with the thickness around one Jupiter radius, R J . The vertical stress balance in the thin current sheet can be partially supported by the local maximum of the shear magnetic field. The amplitude of the corresponding field-aligned current density is comparable with the amplitude of the total current density. The drop of the plasma (electron) density across the thick current sheet is about 50–80% of the density peak value. We investigate horizontal (along the tail) distributions of magnetic field amplitudes B 0 measured at the boundary of the current sheet and magnitudes of the normal component measured in the vicinity of the central region, B n 0 . For r > 50 R J both B 0 and B n 0 vary with the radial distance r as ~ r − 1 , and the ratio B n 0 / B 0 ~ 0.05 – 0.2 is almost constant along the tail (up to 120 R J ). The amplitude of the current density j m 0 and the plasma (electron) density 〈 n e 〉 (averaged across the current sheet) decrease with the same rate ~ r − 1 . Thus, the current bulk velocity v D = j m 0 / e 〈 n e 〉 ≈ 100 km / s is almost constant along the tail. We compare properties of the Jovian magnetotail current sheet with the corresponding properties of current sheets observed in the Earth׳s magnetotail.