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Based on continuous measurements of the atmospheric electric potential gradient (PG) in the Geophysical Observatory at Nagycenk (Hungary), selected data of the interval 1993-2003 have been analysed. The analyses were particularly aimed at the confirmation of global signatures found by a previous study using PG data of a shorter period. The present results have proved that the seasonal variation of PG (generally showing a winter maximum and a summer minimum at land stations) might really be modified at Nagycenk by a secondary maximum appearing in summer-time of certain years. Further analyses have also been carried out by using data derived from measurements with two different apparatus, however, covering a shorter period. Moreover, a  connection between the occasional summer peaks of PG and the occurrences of warm El Niño periods might also be suggested on the basis of results derived from selected PG data and appropriate MEI Indices showing the time history of the ENSO phenomenon for the interval 1993-2003.

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Acta Geodaetica et Geophysica Hungarica
Authors:
A. Ádám
,
P. Bencze
,
F. Märcz
,
D. Martini
,
G. Sátori
,
L. Szarka
,
J. Verő
,
V. Wesztergom
, and
B. Zieger

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.

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Acta Geodaetica et Geophysica Hungarica
Authors:
A. Ádám
,
P. Bencze
,
J. Bór
,
B. Heilig
,
Á. Kis
,
A. Koppán
,
K. Kovács
,
I. Lemperger
,
F. Märcz
,
D. Martini
,
A. Novák
,
G. Sátori
,
S. Szalai
,
L. Szarka
,
J. Verő
,
V. Wesztergom
, and
B. Zieger

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 ( h m 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.

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