A Test of Convection Models for IMF Bz North
Planetary and Space Science
Plasma convection at high latitudes is strongly controlled by the direction of the interplanetary magnetic field (IMF). When the IMF is southward, two-cell convection patterns exist with anti-sunward flow in the polar cap and return flow equatorward in the auroral oval. When the IMF is northward, however, the situation is more complicated and several convection patterns have been proposed to explain the observations of sunward polar cap flow, including three-cell, four-cell, and distorted two-cell patterns. Since the different convection patterns are expected to display different ionospheric signatures, the Utah State University Ionospheric Model can provide insight as to which convection model applies to given situations. The model was run to obtain diurnally reproducible ionospheric densities and temperatures for summer and winter conditions using both distorted two-cell and three-cell convection patterns. Differences due to the different convection patterns manifest themselves in the depth and location of polar holes in the F-region electron density. While the total depth of the model holes is a characteristic of the diurnally reproducible pattern, the features appear and are recognizable within 0.5 h. Langmuir probe data from 41 DE-2 passes, during which the IMF Bz component was northward, have been qualitatively checked against the model predictions. The cross polar cap electron density profiles of a large majority of the passes more closely conform to the distorted two-cell runs for both polarities of the IMF By component. This test can be generalized to rule out proposed convection patterns based on the presence/absence and position of polar electron density holes.
Maynard, N. C., J. J. Sojka, R. W. Schunk, J. P. Heppner, and L. H. Brace, A test of convection models for IMF Bz north, Planet. Space Sci., 38, 1077–1089, 1990.