SOLAR AND IMF EFFECTS ON MIDLATITUDE IONOSPHERIC ELECTRIC-FIELDS AND FOF2

The solar and IMF effects were statistically detected in mid-latitude (L = 1.25) ionospheric electric field data obtained by the MU radar. I t was found that the IMF-B-x component (sector polarity) and the solar radio flux (SRF) correlates with the north-south component of the ele ctric 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 correl ation 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 fa ct it was also found from the data for almost two solar cycles that th e IMF-B-x (or B-y) dependence of the ionospheric foF2 is very similar with the solar activity (sunspot number) dependence of it. This sugges ts 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 field s were also detected by taking the correlations between the time diffe rentials of them and the results are consistent with the known IMF eff ects 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 held is consistent with the penetrati on of the dawn-to-dusk electric field in the magnetosphere indicating the imperfect shielding by the plasmasphere.