The Seasonal Variation of the Direct Current Global Electric Circuit: 1. A New Analysis Based on Long-Term Measurements in Antarctica

It has long been noted that the seasonal behavior of the global electric circuit (GEC) is difficult to reliably determine from measurements of atmospheric electrical parameters, largely owing to prominent annual cycles of aerosols affecting the conductivity in most continental locations. Here we discuss earlier studies in this direction and present further analysis of this problem using the results of potential gradient (PG) measurements at the Vostok station in Antarctica during 2006–2020. Collected at the high and remote Antarctic Plateau, Vostok PG values form a unique continuous data set indicating the variation of atmospheric electricity on different timescales; on the annual timescale the uniformity and consistency of the data turn out to be especially important (in particular, seasonal behavior of GEC parameters at specific UTC hours may be substantially different from the respective diurnal mean variation). PG measurements at Vostok indicate the highest and lowest values of the diurnal mean GEC intensity during the Northern Hemisphere summer and winter, respectively; this variation generally agrees with the available results of air—Earth current measurements. The seasonal variation of the GEC has been previously linked to the annual cycle of insolation; our findings further support this relationship, as it can provide a physical explanation not only for the summer PG maximum observed at Vostok but also for a small local minimum inside this maximum. The dominance of the Northern Hemisphere in the resulting variation is apparently related to the latitudinally asymmetrical distribution of land over the Earth's surface.