MODELS OF FIELD-ALIGNED CURRENTS NEEDFUL TO SIMULATE THE SUBSTORM VARIATIONS OF THE ELECTRIC-FIELD AND OTHER PARAMETERS OBSERVED BY EISCAT

We have used the global numerical model of the coupled ionosphere-ther mosphere-protonosphere system to simulate the electric-field, ion- and electron-temperature and -concentration variations observed by EISCAT during the substorm event of 25 March 1987. In our previous studies w e adopted the model input data for field-aligned currents and precipit ating electron fluxes to obtain an agreement between observed and mode lled ionospheric variations. Now, we have calculated the field aligned currents needful to simulate the substrom variations of the electric field and other parameters observed by EISCAT. The calculations of the field-aligned currents have been performed by means of numerical inte gration of the time-dependent continuity equation for the cold magneto spheric electrons. This equation was added to the system of the modell ing equations including the equation for the electric-field potential to be solved jointly. In this case the inputs of the model are the spa tial and lime variations of the electric-field potential at the polar- cap boundaries and those of the cold magnetospheric electron concentra tion which have been adopted to obtain the agreement between the obser ved and modelled ionospheric variations for the substorm event of 25 M arch 1987. By this means if has been found that during the active phas e of the substorm the current wedge is formed. It is connected with th e region of the decreased cold magnetospheric electron content travell ing westwards with a velocity of about 1 km s(-1) at ionospheric level s.