The physical mechanism of the explicit B y -effect has so far remained poorly understood. It is well known that IMF B y plays important roles in several magnetospheric and ionospheric dynamics. For example, IMF B y affects the geometry of the dayside reconnection (Park et al., 2006;Sonnerup, 1974;Trattner et al., 2012) and exerts magnetic stress on opened field lines, leading to dawn-dusk asymmetries in magnetospheric