Ionospheric convection response to changes of interplanetary magnetic field B-z component during strong B-y component

It is well established that ionospheric convection patterns are strongly co ntrolled by the interplanetary magnetic field (IMF). There has been an incr eased interest in ionospheric convection response to IMF changes. Some stud ies found that ionospheric flows change first near noon and later near the dawn-dusk meridian plane, which is interpreted as propagation or expansion of newly generated convection cells in the cusp region. Other studies showe d that the change in convection pattern in response to IMF reorientations i s spatially fixed. In this paper, we investigate the ionospheric convection response to IMF Bz changes during strong IMF BZ. On March 23, 1995, B-x wa s small, B-y was strongly positive (7-11 nT), and the B-z polarity changed several times after 1300 UT. The dayside ionospheric convection is dominate d by a large clockwise convection cell. The cell focus (the "eye" of the co nvection pattern) is located in the prenoon sector for northward B-z and in the postnoon sector for southward B-z. It is found that the cell focus shi fts from the prenoon sector to the postnoon sector following a southward BL turning and vice versa for a northward B-z turning. However, the motion of the convection cell, or the largest change in the convection pattern, is l imited roughly to the region between the previous cell focus and the new ce ll focus. Outside this region, the ionospheric flows could be greatly enhan ced or weakened, while the convection pattern shape changes very little. Wh en B-y is strong enough, the B-z reorientation causes changes in the flow i ntensity but not in the shape of the convection pattern. The results show t he characteristics of ionospheric convection response during strong B-y and suggest that the convection reconfiguration is not only determined by the changing B-z but also significantly influenced by the stable and large B-y.