AN IONOSPHERIC CONDUCTANCE MODEL-BASED ON GROUND MAGNETIC DISTURBANCEDATA

An attempt is made to construct an improved ionospheric conductance mo del employing ground magnetic disturbance data as input. For each of-t he different regions in the auroral electrojets specified by different combinations of horizontal (Delta H) and vertical (Delta Z) magnetic perturbations, as well as by magnetic local time (MLT), an empirical r elationship is obtained between the ionospheric conductance deduced fr om Chatanika radar data and magnetic disturbances from the nearby Coll ege magnetic station. The error involved in the empirical formula is g enerally of the order of 20-50%. However, some sectors are so poorly c overed that uncertainty estimates;cannot be made. The new formulas are applied to an average magnetic disturbance distribution to deduce the average conductance distribution. This is compared with a conductance model based on electron precipitation data [Hardy et al., 1987], find ing good agreement in terms of the magnitude and distribution pattern. Combining.our empirical relationships with the empirical formulas pro posed by Robinson et al. [1987], the average energy and energy flux of precipitating electrons are also estimated. Notable similarities exis t between the global distribution patterns of these and those obtained by Hardy et al. [1985]. It is proposed that the present conductance m odel can be used to complement more direct measurements in order to ob tain the global distribution needed to study the large-scale electrody namics of the polar ionosphere. Several interesting characteristics ab out the auroral electrojet system are apparent from the empirical rela tionship: (1) For a given magnitude of Delta H, the electric field is relatively stronger in the eastward electrojet region than in the west ward electrojet region. (2) The electric field plays a greater role in the intensification of electrojet current than the ionospheric conduc tance does in the poleward half of the westward electrojet, whereas th e opposite trend is apparent in the equatorward half. However, no such different roles of the electric field and conductance is noticeable i n the eastward electrojet region. (3) The amoral conductance enhanceme nts tend to be largest around midnight, due to more intense particle f luxes there. (4) The mean particle energy depends on MLT but is relati vely insensitive to magnetic activity.