SUDDEN IMPULSES AT LOW LATITUDES - TRANSIENT-RESPONSE

When the magnetosphere is compressed by a sudden change in the solar w ind dynamic pressure, the horizontal component of the Earth's magnetic field is increased at low latitudes. Often there is an overshoot asso ciated with this increase in the field, but not always. The overshoot does not appear to be due to induced currents in the interior of the E arth or in the ionosphere. Rather, its magnitude appears to be control led by both the strength of the ring current, and by local time. We sp eculate that the overshoot in the horizontal component is due to an ov ershoot in the compression of the magnetosphere and that when the ring current is strong the compressional wave is damped and the magnetosph ere is not set into oscillation by the compressional wave.