Monthly Diurnal Global Atmospheric Circuit Estimates Derived from Vostok Electric Field Measurements Adjusted for Local Meteorological and Solar Wind Influences

Local temperature, wind speed, pressure, and solar wind-imposed influences on the vertical electric field observed at Vostok, Antarctica, are evaluated by multivariate analysis. Local meteorology can influence electric field measurements via local conductivity. The results are used to improve monthly diurnal averages of the electric field attributable to changes in the global convective storm contribution to the ionosphere-to-earth potential difference. Statistically significant average influences are found for temperature (-0.47 +/- 0.13% V m(-1) degrees C-1) and wind speed [2.1 +/- 0.5% V m(-1) (m s(-1))(-1)]. Both associations are seasonally variable. After adjusting the electric field values to uniform meteorological conditions typical of the Antarctic plateau winter (-70 degrees C, 4.4 m s(-1), and 623 hPa), the sensitivity of the electric field to the solar wind external generator influence is found to be 0.80 +/- 0.07 V m(-1) kV(-1). This compares with the sensitivity of 0.82 V m(-1) kV(-1) to the convective meteorology generator that is inferred assuming an average ionosphere-to-ground potential difference of 240 kV taken with the annual mean electric field value of 198 V m(-1). Monthly means of the Vostok electric field corrected for the influence of both local meteorology and the solar wind show equinoctial (March and September) and July local maxima. The July mean electric field is greater than the December value by approximately 8%, consistent with a Northern Hemisphere summer maximum. The solar wind-imposed potential variations in the overhead ionosphere are evaluated for three models that fit satellite measurements of ionospheric potential changes to solar wind data. Correlations with Vostok electric field variations peak with a 23-min interpolated delay relative to solar wind changes at the magnetopause.