The association of the European “Little Ice Age” (1550- 1850; Lamb, 1982) with a period of significantly reduced solar activity (Eddy, 1976) suggests a significant mechanism of climate variation remains to be determined. Recent optical observations of connections between the tops of thunderstorm systems and altitudes of 70-90 km (Sentman and Wescott, 1996) demonstrate a linkage between the troposphere and the lower reaches of the ionosphere. If thunderstorm development is affecled by its electrical environment, then solar modulation of the geoelectric field provides a viable solar-variability-climate mechanism (see, e.g., Tinsley 1996). The high, dry Antarctic plateau provides an ideal site for demonstrating that solar variability can influence the geoelectric field. in this paper, we present evidence that the geoelectric field at Vostok is modulated by the duskward component of the Interplanetary Magnetic Field (IMF By) when Vostok rotates under the region magnetically linked to the dayside interaction region between the solar wind and the Earth's magnetic field.