PREDICTION OF GEOMAGNETIC-ACTIVITY

A simple analytic model for the directly driven, adiabatic solar wind- magnetosphere-ionosphere coupling is derived on the basis of frontside reconnection and force balance in the tail. Magnetosphere-ionosphere coupling occurs through Alfven waves which are driven by changes of el ectric fields in the magnetosphere. The model provides an algorithm wh ich calculates the directly driven part of the auroral electrojets fro m an observed solar wind variation. For two days in May 1979 the cross correlation between the prediction and observation of AE is greater t han 0.9. This suggests that most of the geomagnetic activity during th ese two days was directly driven by the solar wind.