Statistical dependence of auroral ionospheric currents on solar wind and geomagnetic parameters from 5 years of CHAMP satellite data

The effects of the solar wind dynamic pressure (P), the z component of the solar wind magnetic field (B(z)), the merging electric field (E(m)), season and the K(p) index on R1 and R2 field-aligned currents are studied statistically using magnetic field data from the CHAMP satellite during 2001-2005. The ionospheric and field-aligned currents are determined from the magnetic field data by the recently developed 1-D Spherical Elementary Current System (SECS) method. During southward IMF, increasing |B(z)| is observed to clearly increase the total field-aligned current, while during northward IMF, the amount of field-aligned current remains fairly constant regardless of |B(z)|. The dependence of the field-aligned current on Bz is given by |I(r)[MA]|=0.054.B(z)[nT](2)-0.34.B(z)[nT]+2.4. With increasing P, the intensity of the field-aligned current is also found to increase according to |I(r)[MA]|=0.62.P[nPa]+1.6, and the auroral oval is observed to move equatorward. Increasing E(m) produces similar behaviour, described by |I(r)[MA]|=1.41.E(m)[mV/m]+1.4. While the absolute intensity of the ionospheric current is stronger during negative than during positive B(z), the relative change in the intensity of the currents produced by a more intense solar wind dynamic pressure is observed to be approximately the same regardless of the B(z) direction. Increasing K(p) from 0 to >= 5 widens the auroral oval and moves it equatorward from between 66 degrees-74 degrees AACGM latitude to 59 degrees-71 degrees latitude. The total field aligned current as a function of K(p) is given by |I(r)[MA]|=1.1.K(p)+0.6. In agreement with previous studies, total field-aligned current in the summer is found to be 1.4 times stronger than in the winter.