A first comparison of POLAR magnetic field measurements and magnetohydrodynamic simulation results for field-aligned currents

This letter presents comparisons between POLAR magnetic field measurements and results from a global numerical simulation of the Earth's magnetosphere using WIND measurements of the solar wind parameters as input. The comparison shows that the simulation provides a good, representation for the magnetic perturbation associated with an upward Region 1 field-aligned current (FAG) in the prenoon sector. This current system is caused by the interplanetary magnetic field (IMF) negative B-y component and also features downward current on open field lines at higher latitudes. The results also show effects caused by a gradual rotation of the IMF northward and a sudden return to its initial dawnward direction. The self-consistent simulation Birkeland current pattern at ionospheric altitudes is also presented, and its evolution caused by the IMF rotations is discussed.