Statistical dependence of auroral ionospheric currents on solar wind and geomagnetic parameters from 5 years of CHAMP satellite data
Abstract. The effects of the solar wind dynamic pressure (P), the z component of the solar wind magnetic field (Bz), the merging electric field (Em), season and the Kp 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 |Bz| 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 |Bz|. The dependence of the field-aligned current on Bz is given by |Ir[MA]|=0.054·Bz[nT]2−0.34·Bz[nT]+2.4. With increasing P, the intensity of the field-aligned current is also found to increase according to |Ir[MA]|=0.62·P[nPa]+1.6, and the auroral oval is observed to move equatorward. Increasing Em produces similar behaviour, described by |Ir[MA]|=1.41·Em[mV/m]+1.4. While the absolute intensity of the ionospheric current is stronger during negative than during positive Bz, 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 Bz direction. Increasing Kp from 0 to ≥5 widens the auroral oval and moves it equatorward from between 66°–74° AACGM latitude to 59°–71° latitude. The total field aligned current as a function of Kp is given by |Ir[MA]|=1.1·Kp+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.