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.

NUMERICAL MODELING OF THE ALASKA 1964 EARTHQUAKE IONOSPHERIC PRECURSORS “P hysics o f Auroral P henom ena", Proc. XXXIII A n n u a l Sem inar, A patity, pp. 1 1 3 -1 1 6 , 2011 © Kola Science Centre, Russian Academy of Science, 2011 Polar Geophysical Institute M.V. K lim enko1’2, V .V . K lim enko2, V .V . B ryukhanov1, and S.A. Pulinets3,4 1Kaliningrad State Technical University, Kaliningrad, Russia, e-mail: vvk_48@mail.ru 2West Department ofN . V. Pushkov IZMIRAN, Kaliningrad, Russia 3Fedorov Institute o fApplied Geophysics, Moscow, Russia 4Institute o f Space Research, RAS, Moscow, Russia Abstract. In this research, we used the numerical experiments for reproduction o f observed changes in the ionosphere prior to strong high-latitude earthquake on Alaska in 1964. As formation mechanism of such ionosphere disturbances, we consider the penetration of the vertical electric field of seismogenic origin from below into the ionosphere, which is connected with occurrence in the ionosphere of electric potential irregularity in the near­ epicenter area. The numerical experiments have shown, that the account of such electric potential irregularity in the ionosphere in near-epicenter area allows reproducing the morphology of ionospheric disturbances observed in the period o f seismic activity. foF2, MHz Introduction Earlier in (Klimenko and Klimenko, 2009) we had been presented the model calculation results of the ionospheric disturbances prior to the strong Alaska Good Friday earthquake of 1964. As formation mechanism of such ionosphere disturbances, we considered the zonal electric field and small- scale internal gravity waves with small amplitude in the near-epicenter area. This earthquake occurred on Friday, March 27 (local time). It happened at a point with coordinates 61.1° N and 147.6° W, had a magnitude Mw=9.2 and became one of the first earthquake on which the ionospheric researchers have turned a fixed attention (Davies, Baker, 1965; Leonard, Barnes, 1965). In the given research as formation mechanism of ionosphere disturbances prior to this strong earthquake, we considered the penetration of vertical electric field of seismogenic origin from lithosphere into the Earth’s ionosphere. Formation mechanism of local large-scale ionospheric precursors of earthquakes From the analysis of research results (see reviews e.g. Liperovsky et al., 1992; Pulinets, Boyarchuk, 2004; Hayakawa, 2007; Liperovsky, 2008), submitted by Klimenko and Klimenko (2009), it follows that as formation mechanisms of ionospheric disturbances prior to earthquakes one can be considered only: 1) the penetration o f seismogenic electric fields into the Earth’s ionosphere; 2) the small-scale IGWs with small amplitude. In (Namgaladze, 2007) it has been come out with the assumption, that the most probable formation mechanism of areas o f disturbed NmF2 and Total Electron Content (TEC), observable prior to strong earthquakes, is the vertical transport o f F2-region ionospheric plasma under the zonal electric field action. The geomagnetic conjugacy o f the ionospheric precursors of earthquakes (Pulinets et al., 2003) is strong argument in favor o f this hypothesis. Besides, the analysis o f model calculation results in (Namgaladze et al., 2009; Klimenko and Klimenko, 2009) testifies in favor of this hypothesis. It is necessary to notice, that the direct penetration of UT, h Fig. 1. Top - diurnal variations in the critical frequency foF2 at Anchorage station during March 24-28, 1964 (solid curve) and March 24-28, 1965 (dotted curve). Vertical line (dashes) marks the underground shock instant on the UT axis. Bottom - calculation results. Circles - without seismogenic sources. Thin and thick lines - with penetrated vertical electric field at electric potential irregularity, which equals 10 and 30 kV, relatively. zonal electric fields o f seismogenic origin into the Earth's ionosphere before strong earthquakes does not yet find the experimental acknowledgement. There is a question, how such zonal electric fields can arise in the ionosphere prior to earthquakes? There is a lot of experimental evidences and theoretical estimations of penetration o f vertical electric field from the atmosphere into the ionosphere before earthquakes (Chmyrev et al., 1989; Grimalsky et al., 2003; Pulinets, Boyarchuk, 2004; Pulinets, 2009). Such penetration o f vertical electric field is connected with the formation o f large-scale irregularity of ionosphere potential over the near-epicenter area. In (Harrison, 2002) it is shown that the potential difference from ground 113