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.
Märcz F, Sátori G, Zieger B 1997: Ann. Geophysicae, 15, 1604--1614.