Showing papers by "Arthur D. Richmond published in 1985"

Interplanetary magnetic field control of high-latitude electric fields and currents determined from Greenland Magnetometer Data

Abstract: To determine the effects of the interplanetary magnetic field (IMF) on the electric potential as well as on ionospheric and field-aligned currents, a recently available numerical algorithm is applied to an empirical model of high-latitude magnetic perturbations, parameterized in terms of the By and Bz components of the IMF. The empirical model is derived from 20-min average magnetometer data observed during summer at the chain on the west coast of Greenland and the corresponding IMF information from the HEOS 2 satellite. The calculated results reproduce fairly well overall features of the influence of the IMF on high-latitude electric fields which have been reported on the basis of more direct measurements. This confirms the validity of the numerical method and the conductivity distribution models. In addition, our results indicate that the system of ionospheric and Birkeland currents near the polar cusp, which has been shown to depend strongly on By, exists independently of the system of region 1 and region 2 field-aligned currents, which, on the other hand, depends strongly on Bz. The direction of the field-aligned currents in the dayside polar cap is uniquely controlled by the sign of the By component of the IMF, namely upward currents for By > 0 in the northern polar cap and oppositely directed for By 0 and By small the ionospheric and field-aligned currents are localized near the dayside polar cusp, and the electric field has a dusk-dawn component in a narrow region near magnetic local noon in agreement with reported satellite measurements. The associated distribution of field-aligned currents consists of the region 1 current system and an additional pair of oppositely directed currents located poleward of the region 1 currents.

Estimation of ionospheric electric fields and currents from a regional magnetometer array

Abstract: We investigate the technique of calculating ionospheric electric fields and currents and field-aligned currents using an equivalent current function obtained from a regional array of ground-based magnetometers at high latitudes (Scandinavian Magnetometer Array). Like similar calculations previously done on a global scale, the derived electric fields and currents are found to depend on the model of ionospheric conductivity assumed. Unlike the global scale calculations, the regional calculations are also dependent on the assumed boundary conditions. Additional information on the electric fields, currents, and/or conductivities is required, besides the ground magnetic variations, to obtain unique estimations of the ionospheric electrodynamic features. In the present case, ionospheric drift measurements from one of the Scandinavian Twin Auroral Radar Experiment radars help constrain the calculations. Analysis of an equivalent current function at 1835 UT on October 7, 1976, representing Harang discontinuity conditions, suggests that upward field-aligned current probably existed near the boundary between eastward and westward electrojets.