Natural Hazards and Earth System Science www.nat-hazards-earth-syst-sci.net 1561-8633 1684-9981 9 1 2009 10.5194/nhess-9-53-2009 http://www.nat-hazards-earth-syst-sci.net/9/53/2009/ http://www.nat-hazards-earth-syst-sci.net/9/53/2009/nhess-9-53-2009.html http://www.nat-hazards-earth-syst-sci.net/9/53/2009/nhess-9-53-2009.pdf 53 59 2009-01-19 Day-time variations of foF2 connected to strong earthquakes E. V. Liperovskaya V. V. Bogdanov P.-F. Biagi C.-V. Meister c.v.meister@skmail.ikp.physik.tu-darmstadt.de V. A. Liperovsky M. V. Rodkin Institute of Physics of the Earth of the Russian Academy of Sciences, Bolshaya Gruzinskaya 10, 123995 Moscow, Russia Institute of Cosmophysical Research and Radio Wave Propagation, Far Eastern Branch of the Russian Academy of Sciences, 684034 Petropavlovsk-Kamchatsky, Russia Physics Department, University of Bari, 70126 Bari, Italy Technische Universität Darmstadt, Institut für Kernphysik, Schlossgartenstr. 9, 64289 Darmstadt, Germany Geophysical Centre of the Russian Academy of Sciences, Molodejnaya 3, 117296 Moscow, Russia The statistical analysis of the characteristic frequency foF2 of the Earth's ionosphere averaged over mid-day hours – from 11:00 till 17:00 h LT – is carried out. Disturbances of foF2 connected to earthquakes are considered on the background of seasonal, geomagnetic, 11-years and 27-days solar variations. A special normalized parameter F is introduced, which represents the almost seasonal-independent part of foF2. 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