The magnetic field structure of the geomagnetic plasma sheet at 30 RE

An analysis of data taken by the NASA-GSFC magnetometer on board the Explorer 34 spacecraft has resolved the structure of the magnetic field in the plasma sheet at 3 R. Time averaging of the data reduces the problem of distinguishing spatial from temporal fluctuations in the magnetic field components. Such an average of the X-sm component (sm denotes the solar-magnetospheric coordinate system), designated BX, serves as an independent parameter and specifies the location of the satellite within the two-dimensional field geometry. A statistical treatment of the convective derivative of BX measured at the satellite and an application of Maxwell's equations indicate that the flux of electric current in the Y direction is uniform at least across the central third of the plasma sheet where |BX|<=1 y The current density becomes more tenuous for larger |BX|. The field-reversal region is observed to occupy a much thicker portion of the plasma sheet than has been reported by other investigators. Examination of the normal component BZ indicates that the field lines undergo gradual curvature as they pass through the plasma sheet. These results are only weakly affected by worldwide geomagnetic activity. Therefore, the basic geometry of the plasma sheet field appears to be the same for both geomagnetically active and quiet periods