GENERATION OF REGION-1 CURRENT BY MAGNETOSPHERIC PRESSURE-GRADIENTS

The Rice Convection Model (RCM) is used to illustrate theoretical poss ibilities for generating region 1 Birkeland currents by pressure gradi ents on closed field lines in the Earth's magnetosphere. Inertial effe cts and viscous forces are neglected. The RCM is applied to idealized cases, to emphasize the basic physical ideas rather than realistic rep resentation of tile actual magnetosphere. Ionospheric conductance is t aken to be uniform, and the simplest possible representations of the m agnetospheric plasma are used. Three basic cases are considered: (I)th e case of pure northward IMF, with cusp merging assumed to create new closed field lines near the nose of the magnetosphere, following the s uggestion by Song and Russell [1992]; (2) the case where Dungey-type r econnection occurs at the nose, but magnetosheath plasma somehow enter s closed field lines on the dawnside and duskside of the merging regio n, causing a pressure-driven low-latitude boundary layer; and (3) the case where Dungey-type reconnection occurs at the nose, but region 1 c urrents flow on sunward drifting plasma sheet field lines. In case 1, currents of region 1 sense are generated by pressure gradients, but th ose currents do not supply the power for ionospheric convection. Resul ts for case 2 suggest that pressure gradients at the inner edge of the low-latitude boundary layer might generate a large fraction of the re gion 1 Birkeland currents that drive magnetospheric convection. Result s for case 3 indicate that pressure gradients in tile plasma sheet cou ld provide part of the region 1 current.