The magnetic effects of magnetosphere surface currents

The electrical currents on the interface separating the geomagnetic field from the solar corona create a magnetic field everywhere interior to the interface. This surface current magnetic field has been computed in the meridian plane on the sunlit side of the earth by integration over the surface currents on the interface. It was found that apart from polar regions the surface current magnetic field increases linearly with altitude. At the subsolar point the increase is from 14 gamma at the earth's surface to 35 gamma at the edge of the magnetosphere during normal solar activity when the altitude of the magnetosphere is at 10 earth radii. If abnormal solar activity lowered the altitude of the interface to 5 earth radii, the magnetic field at the surface of the earth would increase by 135 gamma . A sudden change in interface altitude of 2 earth radii would cause a sudden change in magnetic field at the earth's surface of about 16 gamma . Such a change has been observed. (auth)