MAGNETIC STORM EFFECTS IN THE ATMOSPHERIC ELECTRIC FIELD VARIATIONS

The vertical component (Ez) of the atmospheric electric field variations, measured at middle (obs. Swider) and polar (obs. Hornsund) latitudes under “fair-weather” conditions, have been analyzed. The strong effect of sharp daytime Ez increasing (negative Ez anomalies) in the middle latitudes was found during the main phase of the strong and moderate magnetic storms. The negative Ez deviation started simultaneous with the night side geomagnetic substorm onset. The observed effects could be interpreted as a result of the influence of the strong night side ionosphere conductivity increasing, caused by substorm associated particle precipitation, to the global electrical circuit. In the polar latitudes the Ez enhancement effects of the storm initial phase have been found. Sometimes the positive Ez variations have been observed during so called “polar substorm” development. We also found the polar ground-based Ez enhancement coincided with similar IMF Ey variations. Introduction According to the well established concept, the integrated worldwide thunderstorm activity is considered as a main source of the electric fields in the lower atmosphere. Thunderstorm activity draws current upward from the ground. The ionosphere disperses the current globally, and it leaks back to the surface, averaging a variable potential of~100 V/m at ground level under “fair weather” conditions. One can see in Fig. 1 that the magnetosphere and the ionosphere represent the important part of the global electrical circuit. Variability of the vertical component of the atmospheric electric field (Ez) near the Earth surface has been investigated in many studies. The daily Ez variations are created not only by the worldwide thunderstorm activity, but different solar and geophysical phenomena can provide some influence to Ez behavior. It was suggested that solar activity influences due to ionosphere electric field disturbances may significantly control a global electric circuit state [e.g., Sao, 1967; Apsen et al., 1988, Michnowski, 1998; Bering et al., 1998; Rycroft et al., 2000; Frank-Kamenetsky et al., 2001; Nikiforova et al., 2003]. Although the ionosphere electric potential distribution and atmospheric conductivity variations depend strongly on solar wind change the response to them of the lower atmospheric electric field (Ez) and current (Jz) is still rather not known. Fig. 1 The scheme of the global electrical circuit The strongest manifestations of the solar wind interactions with the magnetosphere and ionosphere processes are especially evident at the auroral and polar latitudes. The most studies of these effects have been curried out at high and polar Arctic and Antarctic areas. Practically, magnetic storm influences, which are distinctly manifested in high latitudes, remained unknown on mid-latitude Ez variations. However, some anomalies in the middle latitude Ez behavior were found during the huge magnetic storm on October 30, 2003 [Nikiforova et al., 2005] showing a possibility to find some Ez effects associated with strong magnetic storms. This was only one event that has to be confirmed or ignored. The aim of this paper is to study possible effects of magnetic storm in atmospheric electric field (Ez) disturbances at middle (obs. Swider) and polar (obs. Hornsund) latitudes. Proceedings of the 7th International Conference "Problems of Geocosmos" (St. Petersburg, Russia, 26-30 May 2008)