Mapping the merging potential from the magnetopause to the ionosphere through the dayside cusp

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Abstract
The pattern in which the potential drop generated at the magnetopause is applied across the polar cap is constructed with the use of two models: the new antiparallel merging model of the dayside magnetopause and the expanding polar cap convection model. The results yield a new set of model convection patterns. Flow into the polar cap begins at a distended, wedge‐shaped cusp, which rotates around the Chapman‐Ferarro cusp position in response to rotation of the IMF in the plane perpendicular to the Earth‐sun line. The length of the wedge base, and the potential drop across it, mapped from the merging line on the magnetopause, decrease as the IMF turns northward. For large IMF y component, rotational flow into the polar cap is distributed along one side of the wedge and feeds into a region of strong east–west flow, some of which turns sharply into the polar cap at the base of the other side of the wedge, at noon. Two convection cells driven by merging with closed geomagnetic field lines exist for all IMF orientations. The cells are confined to a circular polar cap and become distorted with rotation of the cusp, into patterns deduced independently from observations.