Abstract
Abstract. The 11 August 1999 total solar eclipse had been studied using a large array of stations in Central Europe (Bencze et al., 2005). According to the result of this study, the amplitudes of the field line resonance (FLR)-type pulsations decreased in and around the dark spot by about a factor of 2, and this decrease moved with the velocity of the dark spot in the same direction. This decrease was interpreted as a switch-off of the FLR-type pulsations, due to a change in the eigenperiod of the field line as a consequence of a change in the charged particle distribution along the field line. An effect was also found in the phase of the (magnetic or electric) perpendicular components. At the Nagycenk (NCK) observatory lying in the zone of totality, both magnetic and electric records were available. The magnetotelluric (MT) sounding curve computed by the usual method for the eclipse interval (08:00-14:00 UT) fits the previously known standard curve extremely well. During the eclipse, however, impedance values in the FLR period range were highly scattered. The scatter remained as long as the eclipse lasted. Coherence values between magnetic and electric components decreased significantly. In contrast, an earlier similar switch-off of the FLR-type activity on the same day did not cause a similar scatter, in spite of a comparably low coherence. Thus, the lack of FLR-type activity disturbed the usual MT connection between the magnetic and electric components during the eclipse. The induction vector (tipper), especially its real part, shows a clear effect of the eclipse in the FLR period range (24-29 s), too. Both at NCK and at Bad Bergzabern (BBZ, westernmost station and longest FLR period), a definite decrease in the real tipper was ascertained during the totality. The average direction of the tipper did not change. Concerning both parameters, a random effect cannot fully explain the observed phenomena. The scatter of the EM induction parameters is most likely due to the switch-off of the FLR activity. The possibility of such an effect should be considered in induction studies. Pilipenko and Fedotov (1993) supposed an opposite effect and emphasised lower quality data, if resulting from FLR-type pulsations, while we claim high quality data just from such an activity.
Highlights
A total solar eclipse swept over Central Europe, including Hungary, on 11 August 1999 between about 10:00 and 12:00 UT
As the density of the geomagnetic observatories is highest here, and many temporary stations were operated during that time, a unique opportunity was given to study the effect of the eclipse on geomagnetic variations
A similar processing yielded for BBZ low and stable val- The aim of the present study was to investigate the effect of ues for the tipper in the field line resonance (FLR) range
Summary
A total solar eclipse swept over Central Europe, including Hungary, on 11 August 1999 between about 10:00 and 12:00 UT. A part of the upstream waves (UW) penetrates without significant modification into the magnetosphere and reaches the surface, causing UW-type activity there with identical periods at all latitudes Another part excites resonance of the geomagnetic field lines and correspondingly its period increases with increasing geomagnetic latitude (or L-value). This resonance is sensitive to changes in the primary UW spectrum (Veroet al., 1998) and by it, to changes in the IMF. Pilipenko and Fedotov (1993) tried, at first, to separate MT values from UW and FLR activities They assured an opposite effect and emphasised lower quality data, if resulting from FLR-type pulsations, while we claim high quality data just from such an activity.
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