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We investigate with the help of a magnetohydrodynamic (MHD) model how thelarge-scaletopology of the magnetosphere develops for a constant interplanetarymagnetic field (IMF) with differentIMF clock angles and for an IMF By sign change during northward IMF.A detailed examination of the topological changes in the tail and theionosphere for different IMF conditions shows a good agreement withobservational results.The MHD simulations for different constant IMF clock angle casesshow the expected field-line bending and tail twisting for nonzeroIMF By.The tail becomes longer and at its tailward end stronger twisted forIMF Bz>&#x2223;By&#x2223; than for IMF Bz<&#x2223;By&#x2223;. The fieldlines originating in the high-latitude flank of the far-tail plasmasheet map into the near-Earth tail lobes and to a strongly polewarddisplaced polar cap boundary. A comparison with observations suggeststhat an oval-aligned arc may occur on the high-latitude part of thepolar cap boundary.An IMF By sign change causes large deformations of the tail.After the IMF By flip the near-Earth and far-tail plasma sheetregions are oppositely twisted which causes in the near-Earth tail abifurcation of the closed field line region that moves from one flank tothe other.The bifurcated part of the closed field line region maps to a bridgeof closed field lines moving over the entire polar cap. This movingbridge may be interpreted as the mapped region of a movingtranspolar arc. Based on earlier observations, such a type of polararcs is expected to occur after an IMF By sign change. Key words. Ionosphere (auroral ionosphere; ionospheremagnetosphereinteractions). Space plasma physics (numericalsimulation studies

Relation of polar auroral arcs to magnetotail twisting and IMF rotation: a systematic MHD simulation study