Earth magnetotail current sheet near and beyond the Lunar orbit

Abstract:

We analyze the structure of the Earth magnetotail current sheet (CS) in middle, -50 RE<X<-20 RE, and distant, -100 RE<X<-80 RE, regions using dataset of 573 CS crossings by Geotail in 1994-1995. For a subset of 213 CSs we determine the current sheet thickness L, current density amplitude j0 and velocity vD=j0/e n0 (n0 is the plasma density). We analyze dawn-dusk distributions of the CS parameters: L is about 3000 km at the dusk flank and grows up to 12000 km toward the dawn flank; j0 grows toward the dusk flank by a factor of 2-3; the most intense CSs (with higher vD) are observed near the midnight. We show that ion-scale CSs with the thickness of several ion thermal gyroradii (say less than seven) are observed in middle and distant tail regions in more than 50% of crossings. For observed CSs electrons provide likely the dominant contribution to the current density. We divide the subset into intense and weak CSs (using parameter vD). The weak CSs have thickness of about 20 ion thermal gyroradii and Bz of about 1.5 nT. The intense CSs have thickness of about 3-7 thermal gyroradii and much smaller Bz implying a more stretched field line configuration. For intense CSs velocity vD is larger for larger amplitudes of ion bulk velocity vx that is likely due to larger contribution of Speiser ions. Intense CSs may be responsible for the Bursty Bulk Flow generation in the middle and distant tail regions.