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Abstract:
Notwithstanding that the annual cycle of summer and winter is the largest cause of climate variations on Earth, the seasonal variation of the global electric circuit (GEC) is still not known reliably. Both simulations and measurements indicate the existence of a stable universal annual trend in the GEC intensity (just as the Carnegie curve is a stable universal trend on the diurnal timescale), but the trend itself is very difficult to determine.It is hard to infer the annual trend in the GEC from surface potential gradient (PG) measurements at land stations, since they usually show a pronounced maximum during the local winter (and thus imply different results depending on the hemisphere), probably owing to the annual cycle of aerosols, which influence air conductivity. There have been several attempts to deduce the seasonal variation of the GEC by measuring the air—Earth current (rather than the PG), but they also did not yield a comprehensive answer.Here we present further analysis of this problem on the basis of simulations with the WRF weather forecasting model and the INMCM climate model. Simulations clearly demonstrate that the contribution of the equatorial region to the GEC has two maxima in April–May and in November–December, while northern and southern non-equatorial contributions have one maximum during local summer. The resulting annual variation of the GEC, being the sum of three clear trends offsetting each other, is rather subtle, and its prediction in simulations varies depending on the model and parameterisation.
