Empirical models of high-latitude electric fields

Model cross sections of the high-latitude dawn-dusk electric field based on Ogo 6 data are presented for the ‘signature’ profiles (Heppner, 1972c) most frequently encountered for both +Y and −Y orientations of the interplanetary magnetic field. Line integrals give a total potential of 76 keV in each case. The median magnetic disturbance for these models is Kp ≐ 3. To illustrate extremes, examples of model cross sections with total potentials of 23 and 140 keV are also given for periods of Kp = 0 and AE ≐ 1000, respectively. Model convection patterns are also presented by utilizing Ogo 6 data on boundary locations at other magnetic local times. When this information is combined with characteristic field geometries in the region of the Harang discontinuity and is supplemented by data from Ba+ cloud motions in the polar cap, it becomes possible to construct realistic convection patterns on the nightside which deviate from the usual sun-aligned patterns. These modifications are essential because, in general, it is not possible to maintain sun alignment and obtain convective continuity with the geometries observed in the midnight region. The need for empirical models is evident when observations are compared with typical theoretical models. In particular, observed field distributions at and near the polar cap boundary do not resemble the distributions frequently used in theory. The observational models presented are also of limited applicability as a consequence of the variability of observed distributions. These limitations are emphasized, with particular attention given to several types of recurrent deviations which have not previously been discussed.