Measurements of the vertical atmospheric electric field (Ez) at the South Pole between 1982 and 1986 have been analyzed, and the results reveal an important component due to magnetospheric-ionospheric coupling processes. The results are consistent with the theoretical expectation that the ionospheric convection potential patterns in the polar caps, as measured by satellites, are superimposed on the otherwise nearly uniform (but varying in time) global ionospheric potential due to low-latitude thunderstorm sources. The analysis technique was to calculate the ionospheric convection potential from a satellite empirical model, using as input measured solar wind parameters, except that when solar wind data were not available we used as inputs measured ground based magnetic disturbance parameters. We fitted the average low-latitude Ez variation (the Carnegie curve) to the individually measured South Pole Ez diurnal curves. We then subtracted the fitted Carnegie curves from the measured curves and performed a regression analysis of the residual on the calculated ionospheric convection potential values, averaging the data in three hour intervals. Positive correlations with correlation coefficients of about 0.5 were found. Most of the remaining variability in Ez can be attributed to local meteorologically induced noise (especially in winter) and the day-to-day variability of the low-latitude thunderstorm generators. ¿ 1998 American Geophysical Union