Northward interplanetary magnetic field (IMF) causes a reverse convection in the dayside polar ionosphere, i.e., flow having a sunward component at the highest latitudes and anti-sunward flow on both sides of the sunward flow region. Previous studies have shown that this sunward flow region is shifted in the dawn-dusk direction depending on IMF By. This paper reports another new mode of the IMF controlled configuration of the sunward flow region. Seventy-two reverse convection events identified in the Dynamics Explorers 2 dawn-dusk passes were analyzed. Results of statistical analyses show that the sunward flow region expands in the dawn-dusk direction as the magnitude of IMF in the Y-Z plane becomes large. This result can be interpreted by a model which predicts that the dawn-dusk dimension of the high-latitude magnetopause reconnection region from which sunward flow is created extends with the increase of the magnitude of IMF in the Y-Z plane. ¿ 1998 American Geophysical Union