Statistical survey on the magnetic field in magnetotail current sheets: Cluster observations

The distribution properties of the magnetic field in magnetotail current sheets have been explored statistically with the magnetic measurement data of the Cluster mission from June to November of the years 2001-2005. It is found that, on average, the strength of the magnetic field and its B_z component in the current sheet are weaker in the region close to midnight but stronger near the dawnside and duskside flanks, which implies that, in general, a thinner current sheet occurs near midnight and thicker ones near both flanks. The occurrence of tail current sheet flapping is higher on both flanks than in the midnight region, although it is most frequent in the dawn flank. Current sheets with a negative B_z component or a strong B_y component have a higher probability of occurring at magnetic local times of 21:00-01:00, indicating that magnetic activity, e. g. magnetic reconnection and current disruption occur more frequently there. Statistically, the probability distributions of the B_y component and the tilt angle of magnetic field lines in the current sheet are approximately normal distributions, and the occurrence probability of the flattened current sheet is about one third that of the normal current sheet. The magnetic field and B_z component in the current sheet mainly vary from 1 nT to 10 nT. The B_y component in the tail central current sheet is on average twice the IMF B_y at 1 AU.