Magnetic Storm Effects in the Auroral Ionosphere Observed with EISCAT Radar-Two Case Studies

WT5”HZ] Storm time changes of main plasma parameters in the auroral ionosphere are analyzed for two intense storms occurring on May 15, 1997 and Sept. 25, 1998, with emphasis on their relationship to the solar wind dynamic pressure and the IMF B z component.Strong hard particle precipitation occurred in the initial phase for both storms,associated with high solar wind dynamical pressure.During the recovery phase of the storms, some strong particle precipitation was neither concerned with high solar wind pressure nor southward IMF B z .Severe negative storm effects depicted by electron density depletion appeared in the F \|region during the main and recovery phase of both storms, caused by intensive electric field\|related strong Joule/frictional heating when IMF was largely southward. The ion temperature behaved similarly in E\| and F\| region, but the electron temperature did quite different, with a strong increase in the lower E \|region relating to plasma instability excited by strong electric field and a slight decrease in the F \|region probably concerning with a cooling process. The field\|aligned ion velocity was high and apparently anticorrelated with the northward component of the ion convection velocity.