An ionospheric conductance model based on ground magnetic disturbance data

An attempt is made to construct an improved ionospheric conductance model employing ground magnetic disturbance data as input. For each of-the 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 relationship is obtained between the ionospheric conductance deduced from Chatanika radar data and magnetic disturbances from the nearby College magnetic station. The error involved in the empirical formula is generally of the order of 20-50%. However, some sectors are so poorly covered 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], finding good agreement in terms of the magnitude and distribution pattern. Combining our empirical relationships with the empirical formulas proposed by Robinson et al. [1987], the average energy and energy flux of precipitating electrons are also estimated. Notable similarities exist between the global distribution patterns of these and those obtained by Hardy et al. [1985]. It is proposed that the present conductance model can be used to complement more direct measurements in order to obtain the global distribution needed to study the large-scale electrodynamics of the polar ionosphere. Several interesting characteristics about the auroral electrojet system are apparent from the empirical relationship: (1) For a given magnitude of Delta H, the electric field is relatively stronger in the eastward electrojet region than in the westward electrojet region. (2) The electric field plays a greater role in the intensification of electrojet current than the ionospheric conductance does in the poleward half of the westward electrojet, whereas the opposite trend is apparent in the equatorward half. However, no such different roles of the electric field and conductance is noticeable in the eastward electrojet region. (3) The auroral conductance enhancements tend to be largest around midnight, due to more intense particle fluxes there. (4) The mean particle energy depends on MLT but is relatively insensitive to magnetic activity.