Solar wind torque on the geomagnetic cavity

It is argued that the rotation of the ionospheric plasma drives unipolar induction currents through the solar wind plasma in the boundary layer of the geomagnetic cavity. The consequences of this current include a torque on the earth, Joule heating of the ionospheric plasma, and a magnetic field that is mainly eastward in the northern hemisphere and westward in the southern hemisphere. Assuming that all of the magnetic flux from the regions above the auroral zones threads the solar wind plasma in the boundary layer, the torque on the earth at magnetically quiet times is in the neighborhood of 1020 g cm2/sec2;, corresponding to a decrease in the earth's rotation rate of about one part in 1013 per year. The Joule heating rate is of order 1016 ergs/sec compared with the 1018 ergs/sec presently estimated for the dissipation rate associated with the magnetospheric convection.