Magnetotail views at 33RE: IMP 8 magnetometer observations

Abstract

This paper presents magnetic field vector (B) maps, electric current vector (curl B) maps, magnetic force (J×B) 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 −25RE and −40RE in the x direction. Its average x distance was −33RE. 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 9.88RE and is independent of kp. The z profile of current density shows a central peak, 3RE full width at half maximum, and smaller, flanking shoulders. A Harris sheet profile with a 7RE thickness fits the Bx profile. Though these are magnetic field data, the J×B maps clearly outline the plasma sheet. This approach also gives a 7RE 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 J×B 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.