Suggestions in the literature indicate that the observed similarity in ionospheric drifts between Arecibo-summer and Shigaraki-winter and again between Arecibo-winter and Shigaraki-summer are due to conjugate effects owing to the circumstance that the Shigaraki magnetic conjugate point has the same latitude as does Arecibo (in the opposite hemisphere). Here we develop this theory further from one of association to one of cause and effect. We base our explanation on the control of drifts at conjugate locations resting with the location of higher electrical conductance and suggest that this usually results in practice in summer hemisphere control of the winter hemisphere at night, with the daytime case being more complicated. Consequences of our theory are that the Arecibo-summer Shigaraki-winter similarity is, indeed, due to conjugate effects but that the Arecibo-winter Shigaraki-summer similarity has little to do with conjugacy. We combine empirical models of thermosphere and ionosphere structure and dynamics to test our conceptual ideas. We make predictions for such reverse-season similarities for other pairs of incoherent scatter radar locations. ¿ American Geophysical Union 1996