Magnetic configurations of the tilted current sheets in magnetotail

摘要

In this research, the geometrical structures of tilted current sheet andtail flapping waves have been analysed based on multiple spacecraftmeasurements and some features of the tilted current sheets have been madeclear for the first time. The geometrical features of the tilted currentsheet revealed in this investigation are as follows: (1) The magnetic fieldlines (MFLs) in the tilted current sheet are generally plane curves and theosculating planes in which the MFLs lie are about vertical to the equatorialplane, while the normal of the tilted current sheet leans severely to thedawn or dusk side. (2) The tilted current sheet may become very thin, thehalf thickness of its neutral sheet is generally much less than the minimumradius of the curvature of the MFLs. (3) In the neutral sheet, thefield-aligned current density becomes very large and has a maximum value atthe center of the current sheet. (4) In some cases, the current density is abifurcated one, and the two humps of the current density often superpose twopeaks in the gradient of magnetic strength, indicating that the magneticgradient drift current is possibly responsible for the formation of the twohumps of the current density in some tilted current sheets. Tilted currentsheets often appear along with tail current sheet flapping waves. It isfound that, in the tail flapping current sheets, the minimum curvatureradius of the MFLs in the current sheet is rather large with values around1 R_E, while the neutral sheet may be very thin, with its half thicknessbeing several tenths of R_E. During the flapping waves, the current sheetis tilted substantially, and the maximum tilt angle is generally larger than45°. The phase velocities of these flapping waves are several tenskm/s, while their periods and wavelengths are several tens of minutes, andseveral earth radii, respectively. These tail flapping events generally lastseveral hours and occur during quiet periods or periods of weakmagnetospheric activity.