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.