Several recent studies show the possibility of an important connection between the Earth's rotational motion and the number of earthquakes (Stavinschi and Souchay 2001, Shanker et al. 2001). We discuss the long-term periodic variations (30 years and 60 years) in these two geophysical processes, as well in solar activity and the Sun's celestial orbit. The similarities in such periodicities suggest that solar system dynamics may contribute to both solar and geophysical phenomena.
This is a summary of the activities of the Geophysics Department of the Geodetic and Geophysical Institute in the framework of the Scientific School Earth Electromagnetism. Ten reports cover the most important topics and emphasize interconnections between the different phenomena. The topics include interplanetary space, magnetosphere and ionosphere, electromagnetic waves in a wide spectrum, and electromagnetic induction, also within a wide range of frequencies and applications. Geomagnetism, especially the Széchenyi István Geophysical Observatory Nagycenk with a lot of different recordings of electromagnetic parameters play important roles in most topics.
The paper describes research in geomagnetism and aeronomy carried out in the framework of a project organized by the Geodetic and Geophysical Research Institute of the Hungarian Academy of Sciences. It includes the development of the instrumentation of the Nagycenk Geophysical Observatory (geomagnetic measuring systems, ionosonde), moreover other instrumental and methodological developments, too. Observatory data are available in a database. Based on results of the Nagycenk and Tihany observatories and on data of permanent and temporal networks, long-term trends of different electromagnetic parameters were investigated. Thus geomagnetic activity was found secularly increasing, a decrease of the atmospheric electric potential gradient and a 11-year modulation of the winter/December attenuation of the geomagnetic pulsation activity were confirmed. Several possibilities (pulsations, whistlers, modelling) were used to improve knowledge about structure and parameters of the magnetosphere. Electromagnetic precursors of earthquakes were looked for. A significant increase of understanding was obtained in connection with Schumann resonances and electromagnetic transients caused by lightning. It was shown that see-coasts influence characteristically changes in ionospheric trends (
F2). When looking for the effect of the global climate changes in the subsurface electric resistivity, an example was discovered for the decrease of the resistivity due to infiltrating water from precipitation. Electromagnetic exploration of tectonically conditioned weak zones was continued, too.