The effects of a magnetic By component on geomagnetic tail equilibria

Positive correlations of the magnetic y component of the IMF with those of both the magnetotail lobes and plasma sheet show a B{sub y} component pervading the quiet magnetotail with enhanced strength near the neutral sheet (z = 0). A model constructed using linear solutions to the Grad-Shafranov equation for two-dimensional tail equilibria explains these and related observations in terms of MHD equilibrium theory. The authors conclude that the enhanced B{sub y} values must be an essential part of the quiet magnetotail and do not result from a simple intrusion of the IMF. The B{sub y} field consists of a constant background component plus a nonuniform field existing only in the plasma sheet, where it is dependent on the plasma parameter {beta} and the strength of the magnetic B{sub Z} component. B{sub y} is strongest at the neutral sheet and decreases monotonically in {+-} z direction, reaching a constant tail lobe value at the plasma sheet boundaries. Field lines are tilted about the tail axis with the angle of ascent in the y-z plane being greatest at z = 0. This is also the region of greatest field line rotation in the x-y plane, insuring that magnetic reversal always occursmore » near the neutral sheet. The maximum change in field direction between tail lobes is less than 180{degrees} with field lines most closely aligned with the tail axis at the plasma sheet boundaries. The presence of a significant positive B{sub y} component produces currents, including field-aligned currents, that flow through the equatorial plane and toward and away from earth in the northern and southern halves of the plasma sheet, respectively.« less

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