Lobe cell convection as a summer phenomenon

Abstract

Patterns of average potential over the high‐latitude ionosphere in winter show that the dusk convection cell dominates the dawn cell, consistent with the presence of a day‐night conductivity gradient, as predicted by a number of models. However, in the summer hemisphere, when IMF B y is strongly positive, the dusk cell so dominates the dawn cell that the latter nearly disappears; and when IMF B y is strongly negative, the cells are most nearly equal. The difference between winter and summer can be explained by the addition in summer of a single lobe cell, that is, a cell confined to open field lines, circulating within the dusk cell of the two‐cell pattern when B y is positive and within the dawn cell when B y is negative. The result is consistent with predictions of the overdraped lobe model, that lobe cells occur in only one hemisphere at a time, and that their occurrence is controlled by dipole tilt.