Physics of auroral phenomena : proceedings of the 33rd Annual seminar, Apatity, 02 - 05 March, 2010 / [ed.: A.G. Yahnin, A. A. Mochalov]. - Апатиты : Издательство Кольского научного центра РАН, 2011. - 206 с. : ил.

“P hysics o f Auroral P henom ena“, Proc. XXXIII A n n u a l Sem inar, A patity, pp. 1 6 7 -1 7 0 , 2011 © Kola Science Centre, Russian Academy of Science, 2011 Polar Geophysical Institute SUBSTORM EFFECTS IN THE POLAR LATITUDE ATMOSPHERIC ELECTRIC FIELD DISTURBANCES N.G. Kleimenova1, O.V. Kozyreva1, M. Kubicki2, S. Michnowski2 1Institute o f the Earth Physics RAS, Moscow, Russia 2Institute o f Geophysics PAS, Warsaw, Poland Abstract. The variations of the vertical component of the near-Earth atmospheric electric field (Ez), observed at the polar latitude obs. Homsund (Spitsbergen, HOR, Ф=74°) in 2004-2006, caused by substorms have been performed. To avoid local meteorological influences we used Ez data, obtained only under so called “fair weather” conditions, it means the absence o f snow, fog, lower cloudiness, strong wind, negative Ez values. These limitations are o f special importance at polar latitudes. The long lasting “fair weather” periods occur seldom in the polar latitudes. To avoid season effects we analyzed the equinox data, when near-Earth exchange layer is absent and turbulent convection currents are in sig n ific a n t For the analysis we selected 12 morning and 10 evening substorms observed at obs. Homsund. We found that the substorm development both at the auroral latitudes as well as at the polar ones can cause strong perturbations in the atmospheric electric field. These Ez disturbances, measured at Homsund, were positive (Ez values increased) in the local morning and negative (Ez values decreased) in the local evening. The sign of Ez deviations depended on the observatory location relative to the position of the positive or negative plasma convection cells in the polar ionosphere. It is well known that the two cell pattern is most clear during the substorm. In terms of electric fields the evening Ez negative deviations associated with an increasing of the northward directed electric field in the ionosphere and the morning positive Ez variations - with ionosphere electric field directed southward. The observed effects are the result from the penetration of electric fields of an enhanced polar convection to the Earth surface. 1. Introduction The substorm effects in the atmospheric electric field (Ez) variations at auroral latitudes were reported in many previous papers [e.g., Sao, 1967; Olson, 1971; Bandilet et a l, 1986; Michnowski et a l, 1998, Kleimenova et a l, 1998; Belova et a l, 2001, Kozyreva et a l, 2007]. It was shown that at auroral latitudes the bay-like Ez negative deviations are often observed simultaneously with night-time substorm development. Contrary to that, Michnowski et a l, (1991) reported the event observed at the polar latitudes (obs. Homsund) in which there was the positive atmospheric electric field (Ez) variation during the night-time substorm onset. The aim o f the present work was to continue the studying the possible effects of the evening/night and morning substorms in the Ez variations at the polar latitudes. We based our analysis on the ground Ez observations at Homsund observatory at Spitsbergen archipelago (HOR, Ф' = 74.0°, A' = 110.5°). 2. Observations Under magnetically quiet conditions, the observatory Homsund is projected into the polar cap region in the night-time and into the region of the polar cusp in the daytime. Under magnetically disturbed conditions, the auroral oval moves toward lower latitudes, and this observatory appears under the polar cap region projection independently of the local time. In our analysis we used only the Ez data obtained under the so called “fair weather” conditions. This means the absence of a strong wind (the wind velocity is higher than 6 m/s), low cloudiness, precipitation (snow or rain), snowdrift, fog, etc. These limitations are of special importance at the polar latitudes, where motion of snow and ice particles, suspended in an air flow, results in the generation o f considerable electric fluctuations, which significantly exceed the effects of the magnetospheric and ionospheric sources [Guglielmi et a l, 1994; Bums et a l, 1995; Frank-Kamenetsky et a l, 2001]. Not more than 10-15% o f the Ez registration satisfies the “fair weather” conditions at Homsund. An electrostatic fluxmeter, i.e., a rotating dipole (field mill), is used to register Ez variations at Homsund. The equipment was described in detail by Kubicki, (2001). We analyzed the Ez data in 2004—2006 for the near equinoxes (March, October, and November) in order to eliminate the seasonal effects. During these months, in the polar latitudes, the near-Earth exchange layer is absent and turbulent convection currents are insignificant [Park, 1976]. For the detail analysis we selected 12 morning and 10 evening substorms. We found that the substorm development at the auroral latitudes as well as at the polar ones can cause the strong perturbations in the atmospheric electric field at HOR. These Ez disturbances were positive (Ez values increased) in the local morning and negative (Ez values decreased) in the local evening. Two events (03-04.11.2004 and 03-04.09.2006) of morning and evening sustorms are shown in Fig. 1. There are also presented the magnetograms from several stations, located approximately along the same meridian: two polar observatories (NAL, Ф =76°, and HOR, Ф = 74°) and two auroral observatories (SOR, Ф 167