High-latitude field-aligned currents patterns in connection with magnetospheric structure

Distributions of field-aligned currents J∥ determined from surface geomagnetic field variations are projected to the magnetospheric tail and the equatorial cross section of the magnetosphere. The field-aligned currents are calculated under various conditions in interplanetary space. The effects of various ionospheric conductivity distributions on the J∥ pattern is also considered. The high-latitude system of field-aligned current (Region 1) projects onto the plasma sheet of the magnetospheric tail and to the magnetospheric regions in the immediate proximity to the magnetopause for Bz = By = 0. The field-aligned currents of opposite direction in the lower-latitude region (Region 2) are located completely in the closed magnetosphere and can only be projected onto its equatorial cross section. The boundary between Regions 1 and 2 of the field-aligned currents projects to the area near the inner boundary of the plasma sheet. For the condition with B = −4nT and By = 0, the inflow and outflow of the field-aligned currents at ionosphere altitudes are associated with the same magnetospheric regions. For Bz = 4nT and By = 0 an additional system of high latitude field-aligned currents appears, which flows into the afternoon sector and away from the prenoon sector. These currents project to the high-latitude region of the mantle near the magnetopause. When Bz = 0 and By = ±6nT the field-aligned currents with the same direction cover the near-noon sector from the dusk to dawn hours in both the mantle and the equatorial cross-section of the magnetosphere. The field-aligned current directions in these regions are opposite and systematically reverse with changing By polarity. The three-dimensional current systems coupling the magnetosphere and the ionosphere under various conditions in interplanetary space are discussed. These systems are consistant with the distribution of the ionospheric currents which are shown by ground-based observations to close the large-scale field-aligned currents. Field-aligned current systems are proposed according to the regions of their generation in the magnetosphere and depending on the interplanetary conditions.