Variations in polar rain flux according to IMF geometries observed by STSAT-1

We examined polar rain flux observed by STSAT-1 in the northern polar cap and compared it with solar wind parameters. We found that the differential energy spectrum of polar rain was similar to that of the solar wind for the energy range 100 eV – 1 keV, although we cannot rule out the possibility of a small amount of acceleration. On the other hand, the low-energy component of the solar wind showed no correlation and, naturally, the solar wind density had only a weak correlation with the polar rain flux. Polar rain flux in the northern hemisphere is most significant for the condition of the interplanetary magnetic field components Bz < 0, Bx < 0, and By > 0, and in this case it correlated well with the magnitude of By and Bz. For other interplanetary magnetic field conditions, the correlation was insignificant. The results are consistent with those reported previously.