Z. Kaymaz, G. L. Siscoe, N. A. Tsyganenko, R. P Lepping

Department of Atmospheric Sciences, University of California, Los Angeles

This paper presents magnetic field vector (B) maps, electric current vector (curl B) maps, magnetic force (JxB) contour maps, and total field contour maps covering the full tail cross section in the yz plane. The maps are based on 16 years of 5-min averages of IMP 8 magnetic field data. During this time, IMP 8 traversed the tail between -25 R_E and -40 R_E in the x direction . Its average x distance was -33 R_E. For this average distance we show separate maps for low and high dipole tilts, corresponding to equinox and northern hemisphere summer seasons. The low-tilt (equinox) maps show symmetrical field and current patterns; the high-tilt (solstice) maps show the cross-tail current sheet arcing above the equatorial diagonal in the center and dipping below it on the flanks. The shape of warped current sheet fits Fairfield's (1980) displaced ellipse model fairly well. The distance at which the current sheet is hinged to the magnetic equator is found to be 9.88 R_E and is independent of K_p. The z profile of current density shows a central peak, 3 R_E full width at half maximum, and smaller, flanking shoulders. A Harris sheet profile with a 7 R_E thickness fits the B_x profile. Though these are magnetic field data, the JxB maps clearly outline the plasma sheet. This approach also gives a 7 R_E thickness. Many of the average field and current features inferred and demonstrated in earlier studies are confirmed here; some of them are seen for the first time in full cross-section view. Among new features revealed are a large current vortex in the winter hemisphere lobe, a dawn-dusk asymmetry in the JxB force in the plasma sheet (it is stronger on the duskside), and a separation of the cross-tail current sheet into core and wing parts.

J. Geophys. Res., 99, No. A5, 8705-8730, May 1994