Magnetospheric convection induced by interplanetary magnetic-field variations

The dependence of the polar-cap magnetic disturbance on the polarity and magnitude of the Z-component of the interplanetary magnetic field is investigated by regression analysis using hourly values. The Svalgaard-Mansurov effect has been eliminated assuming a linear dependence on the Y-component of the interplanetary field. It is shown that as the northward component of the interplanetary magnetic field increases, a characteristic current system appears in the polar cap. This current system is composed of two current vortices in the dayside polar cap, one in the pre-noon sector and the other in the afternoon sector. The current direction is antisunward in the central polar cap, suggesting that the sunward plasma convection is induced in the polar cap. Current intensity is strongest at phisub(M) approximately 840 around the noon meridian. (Auth.)