Models of high-latitude electric potentials derived with a least error fit of spherical harmonic coefficients


  • D. R. Weimer


New models of the high-latitude electric potentials have been developed. These models show how the polar ionospheric electric field, or plasma convection, responds to changes in the interplanetary magnetic field (IMF) and other parameters, such as dipole tilt angle. These patterns were derived from measurements of the electric field on the DE 2 satellite, using all polar cap passes during which high-resolution IMF data were available from the ISEE 3 or IMP 8 satellites. The data are sorted according to the angle of the IMF in the GSM Y-Z plane. The measurements are further divided into different groups according to the magnitude of the IMF or the dipole tilt angle. All measurements in each group are then used to derive a model of the electric potential for the given conditions, using a new technique where the coefficients of a spherical harmonic expansion are found by least square error fits. The resulting convection patterns are very realistic and show consistent variations as the IMF BY/BZ angle rotates. For northward IMF (positive BZ) evidently there are four convection “cells,” rather than a distortion of the two-cell pattern. Many other useful facts regarding the solar wind-ionosphere coupling can be extracted from the derived patterns, such as the relationship between the polar cap potential drop and the IMF clock angle.