Solar and IMF Effects on Mid-Latitude Ionospheric Electric Fields and foF2

Abstract

The solar and IMF effects were statistically detected in mid-latitude (L = 1.25) ionospheric electric field data obtained by the MU radar. It was found that the IMF-B_x component (sector polarity) and the solar radio flux (SRF) correlates with the north-south component of the electric field on the night-side. For more positive (sunward) B_x, or for greater SRF, the electric field is more southward/downward. However, strong mutual correlation between the IMF-B_x and the SRF is found in the period analyzed (1987-1993), suggesting that the night-side correlation between electric fields and IMF-B_x comes from the effect of the solar activity rather than the direct influence of the IMF-B_x. In fact it was also found from the data for almost two solar cycles that the IMF-B_x (or B_y) dependence of the ionospheric foF2 is very similar with the solar activity (sunspot number) dependence of it. This suggests that the mutual correlation between the solar activity and the IMF-B_x, (or B_y) causes the apparent correlation of the foF2 with the IMF-B_x which has been reported as a sector polarity effect. On the other hand, the direct effects of the IMF-B_x (or B_y) on the electric fields were also detected by taking the correlations between the time differentials of them and the results are consistent with the known IMF effects on the S_q focus location. The differentials of the IMF-B_z have significant correlation with the electric fields in limited local time zones and the sense of electric field is consistent with the penetration of the dawn-to-dusk electric field in the magnetosphere indicating the imperfect shielding by the plasmasphere.