SHORT-TERM CHANGES IN ATMOSPHERIC ELECTRICITY ASSOCIATED WITH FORBUSHDECREASES

Atmospheric electric potential gradient data in Hungary (covering abou t three decades) have been analysed by the superposed epoch method at times of Forbush decrease events. At first, key days were selected on the basis of two lists published recently. The potential gradient show ed, on average, a minimum on the key days if the two lists defined an event on the same day. The character of the potential gradient variati on changed in the cases of events defined by one of the lists one or t wo days later or earlier in comparison with the other list; however, t he potential gradient responded in the same sense. A further analysis based on an extended list confirmed these results. In spite of the hig h noise level in surface atmospheric electricity measurements, suitabl e data selection and treatment helped to detect a decrease of the pote ntial gradient associated with Forbush decreases. Nevertheless, the ti ming of the events and the criteria used for their selection seem to p lay an important role as regards the results obtained. The present res ults are discussed and compared with previously published results in t his area. (C) 1997 Elsevier Science Ltd.