IMF sector effects on the polar geomagnetic field, particularly in winter, are examined with a use of the geomagnetic data from 13 northern and 6 southern high-latitude geomagnetic stations. Detailed behavior of the winter reversal of the sector effects near 70¿ invariant latitude is investigated. A method to improve the sector estimation from geomagnetic data is suggested, and formation of the winter reversal is briefly discussed, taking electric-field propagations along field lines from the summer hemisphere as well as upward and downward field-aligned electric current effects into consideration.