Auroral electrodynamics at the cusp/cleft poleward boundary during northward interplanetary magnetic field

Combined latitude profiles of optical aurora, magnetic disturbances, particle precipitation and field‐aligned currents are used to investigate the electrodynamics of the cusp/cleft ionosphere during northward interplanetary magnetic field (Bz = 12 nT; By = −17 nT). An active zone of strong azimuthal plasma convection, manifested by the Svalgaard‐Mansurov effect in ground magnetic deflections (due to Hall current between pairs of Birkeland currents) and auroral structure at the poleward boundary of the cusp/cleft is observed within ∼ 1030–1230 MLT. Contrary to the typical cusp/cleft auroral activity during negative IMF Bz the discrete auroral forms in the present case move into the cusp/cleft arc, from the poleward edge. Both the optical observations and the inferred field‐aligned current/plasma flow pattern indicate a generator mechanism poleward of the cusp/cleft (i.e. associated with the plasma mantle), giving rise to strong momentum transfer and discrete electron precipitation within a ∼ 200 km wide latitudinal zone at the cusp/cleft poleward boundary, at the time of a poleward moving cusp/cleft arc. From this and other similar studies of the cusp/cleft ionosphere, we conclude that a qualitatively similar mode of solar wind‐magnetosphere interaction is operating both during northward and southward IMF.