Short-term changes in atmospheric electricity associated with Forbush decreases

Abstract

Atmospheric electric potential gradient data in Hungary (covering about 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 showed, 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 variation changed in the cases of events defined by one of the lists one or two days later or earlier in comparison with the other list; however, the potential gradient responded in the same sense. A further analysis based on an extended list confirmed these results. In spite of the high noise level in surface atmospheric electricity measurements, suitable data selection and treatment helped to detect a decrease of the potential gradient associated with Forbush decreases. Nevertheless, the timing of the events and the criteria used for their selection seem to play an important role as regards the results obtained. The present results are discussed and compared with previously published results in this area. © 1997 Elsevier Science Ltd.