A model of region 1 field-aligned currents dependent on ionospheric conductivity and solar wind parameters

Using a paraboloid model of the magnetosphere, we compute the potential dro p across open field lines as a function of the interplanetary magnetic fiel d strength and direction as well as of solar wind velocity and density. The collisionless conductivity of the magnetosheath plasma near the magnetopau se determines the efficiency of the solar wind electric field penetration i nto the magnetosphere. This reconnection efficiency is generally about 0.1. Thus about one tenth of the total potential produced over the magnetospher ic cross section penetrates the polar cap. Knowing the potential drop acros s the polar cap allows us to determine the strength of the region 1 field-a ligned currents as a function of ionospheric conductivity. We compute the m agnetic field disturbance produced by the region 1 field-aligned currents b y using a simple current loop in which the region 1 field-aligned currents close through ionospheric and magnetopause currents. The region 1 field-ali gned currents decrease the magnetic field strength on the dayside of the ma gnetosphere, moving the cusp to lower latitudes. This corresponds to a sunw ard displacement of the polar cap and polar oval. The displacement of the p olar oval is 8 degrees on the dayside and about 3 degrees on the nightside when the total strength of the region 1 Birkeland currents is 5 MA.