The interaction of the solar wind with the Earth's magnetosphere during a northward interplanetary magnetic field was studied by using a three-dimensional magnetohydrodynamic model. For a northward interplanetary magnetic field of 5 nT, the plasma sheer thickens near the noon-midnight meridian plane. When projected onto the polar cap this appears as a narrow channel extending from midnight towards noon. This plasma pattern is associated with three pairs of convection cells. The high latitude sunward convection and northern Bz Birkeland current are caused by magnetic merging in the polar region.