F. Märcz

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.

Whistler ducts and geomagnetic pulsation resonant field line shells near L = 2—are they identical?

Abstract Data from the processing of about 1700 whistlers recorded in Tihany ( L -value of propagation, equatorial electron density and tube content) are compared with geomagnetic pulsation characteristics (mainly of periods) as recorded at the nearby Nagycenk Observatory ( L ∼2). In addition, the number of whistlers recorded at Panska Ves (Czech Republic) for more than ten years (1971–1979, 1987, 1990) are compared with the Nagycenk pulsation activity. Both results can be reconciled with the supposition that whistler ducts and geomagnetic field line shells are closely connected with each other as they appear simultaneously with enhanced probability, and the position of these structures is similar within the magnetosphere.

Pearl-type micropulsations at mid-latitude; their relation to whistlers, solar and geomagnetic activity as well as ionospheric absorption

The occurrence of pearl-type (Pc 1) micropulsations recorded at the mid-latitude station Nagycenk (Hungary) during a half solar cycle showed a quite regular variation on this long time scale. Around solar activity maximum, the number of days with Pc 1 occurrence was rather low, while it began to increase during medium solar activity rising to a maximum around solar activity minimum. Pc 1 pulsations have been analyzed in relation to further parameters and on a shorter time scale, too. Based on data of 2 years with maximum Pc 1 occurrence (around solar activity minimum in 1985 and 1986), a seasonal variation was also found. Additionally, it was confirmed that pearl-type micropulsations might frequently occur, on and after days, with geomagnetic disturbances. At Nagycenk, the selected geomagnetic disturbances were generally associated with an increased ionospheric absorption of radio waves caused by enhanced ionization due to particle precipitation from the magnetosphere into the lower ionosphere. Whistler observations carried out at Panska Ves (a station in the Czech Republic) showed a significant whistler activity connected with these geomagnetic disturbances, however, no after-effect appeared in whistler activity. One of the main goals of the present study was to find a relationship between Pc 1 pulsations and whistlers. Results revealing an increased whistler activity associated with Pc 1 occurrences confirm our previous findings rather convincingly. The latter ones hinted at the probability that certain magnetospheric configurations, e.g. geomagnetic field line shells and whistler ducts are closely connected, as similar positions of the two structures were found within the magnetosphere when characteristics of Pc 3 pulsations and whistlers were analyzed.

Surplus of negative charge flow in point-discharge current as shown by variations on different time scales at Nagycenk station

Abstract Data of point-discharge current measurements at the Nagycenk station covering more than three decades have been used for demonstrating the variations of this atmospheric electric parameter on different time scales. The diurnal variation of the point-discharge current shows an early morning minimum and an afternoon maximum as represented by charges brought down to ground by a metal point (elevated to a height of about 8 m), and this is valid for charges of both signs. On the diurnal time scale, there is a surplus of negative charge flow which peaks in the afternoon. A predominance of negative charge flow was also found on the annual time scale as indicated by the monthly mean values of transported charges of both signs. The monthly mean ratio of negative to positive charge is well above 1.0 from April to October and it is below 1.0 merely in the first three months of the year. Determining an average ratio of negative to positive charge for each individual year between 1961 and 1996, it was shown that the yearly average ratio is usually above 1.0 (except for 4 years). Some comparisons between results of Nagycenk and those obtained simultaneously at other stations showed a certain agreement; however, they also revealed discrepancies between individual values of the transported charges. Notwithstanding, a surplus of negative charge flow was detected even by these comparisons. The results derived on different time scales do confirm that point-discharge current plays an important role in the transfer of charges to the Earth; at the same time a predominance of negative charge flow could be proved.