A theoretical investigation of the generating mechanisms of the disturbance E ¿ B drifts observed at mid-latitudes in performed, with the purpose of understanding the local time dependence of the average disturbance drifts observed above Saint-Santin (L=1.8, 47¿ geomagnetic latitude) and of extending if to other latitudes. To this end, the middle- and low-latitude effects of the two possible generators of electric field disturbances, the solar wind/magnetosphere dynamo, and the ionospheric wind disturbance dynamo, computed by means of a numerical dynamo model of the ionosphere, are systematically compared with the Saint-Santin disturbance drift pattern. The solar wind/magnetosphere dynamo is simulated as an electrostatic potential generator at 75¿ latitude, and its local time dependence determined by least squares fitting the drifts calculated at 45¿ latitude to the observed drift pattern. When the solar wind/magnetosphere dynamo only is considered, the best fit is found for a diurnal sinusoidal shape of the 75¿ latitude potential corresponding to a 40 kV total potential drop across the polar cap rotated by 2 hours eastwards from the dawn-dusk direction. But this source reproduces only one half of the 34-m/s westward steady component observed in Saint-Santin average disturbance drifts. The remaining gap can be filled by inclusion of Blanc and Richmond's (1980) disturbance dynamo electric field model into the fitting procedure. This fitting procedure provides a global theoretical pattern of disturbance electric fields and E ¿ B drifts within the plasmasphere that can be compared with observations. Three latitude zones can be distinguished in the resulting picture. In the external regions of the plasmasphere, one finds an extension of the usual picture of high-latitude plasma drifts, eastward in the morning and westward in the afternoon. The calculated drifts compare fairly well with the drifts disturbance models produced from whistler data at L=4 and from the Millstone Hill radar. At mid-latitudes, between 55¿ and 20¿ invariant latitude, we predict that the superposition of the two dynamos produces westward drifts at all local times; this is consistent with the Saint-Santin and Arecibo radar drift data.