Response of the equatorial ionosphere to solar magnetic sector crossing

A superposed epoch analysis has been carried out of h′F values at Kodaikanal (10°14′N, 77°28′E, dip 3.0°N) pertaining to years of high sunspot activity using solar wind sector boundary passages past the earth as key days. It is found that there is a reduction in h′F values at 2000 LT 1 or 2 days after the sector boundary crossing. The amplitude of this effect which is noticed with both (+, −) and (−, +) sector boundary crossings is higher in equinoxes than in solstices. The response of the equatorial F region to sector boundary crossing seems to originate from perturbations of the equatorial east–west electric field in the post-sunset period associated with the enhancement in geomagnetic activity in the wake of sector boundary crossing.

Response of the mid-latitude ionosphere to solar magnetic sector crossing

Using sector boundary passages past the earth as key days, a superimposed epoch analysis has been carried out of Total Electron Content, foF2 and hpF2. It is found that there is an enhancement of Total Electron Content on the key day for toward-to-away (−, +) sector boundary crossings only, and that this effect is greater in winter (~ 15%) than in summer (~ 10%). The correlation with (−, +) solar magnetic sector crossings (SMSC) seems to derive from the Svalgaard–Mansurov effect but the reason for seasonal effects remains in doubt.