Ionospheric behaviour over Europe during the solar eclipse of 3 October 2005

Kurzfassung

An annular eclipse occurred over Europe in the morning hours of 3 October 2005. The well-defined obscuration function of the solar radiation during the eclipse provided a good opportunity to study the ionospheric/thermospheric response to solar radiation changes. Since the electron density peak behaviour of the ionospheric F2 layer follows the local balance of plasma production, loss and transport, the ionospheric plasma redistribution processes significantly affect the shape of the electron density profile. These processes are discussed here based on a comparison of vertical sounding and vertical total electron content (TEC) data above selected ionosonde stations in Europe. The equivalent slab thickness, derived with a time resolution of 10 minutes, provides relatively good information on the variation of the electron density profile shape during the eclipse. The computations reveal an increased width of the ionosphere before the maximum phase. As indicated by the available measurements over Spain, the photo production is significantly reduced during the event leading to a slower increase of the total ionization in comparison with the neighbouring days. The supersonic motion of the Moon’s cool shadow through the atmosphere may generate atmospheric gravity waves that propagate upward and are detectable as travelling ionospheric disturbances in ionospheric heights. High frequency (HF) Doppler shift spectrograms were recorded during the eclipse showing a distinct disturbance in the band of maximum eclipse. However, it is almost not distinguishable outside this band, which is a different result obtained from previous eclipses. Whereas ionosonde and HF Doppler measurements show enhanced wave activity, the TEC data analysis doesn’t, indicating that the wave amplitudes are too small for detecting. The total ionization reduces up to about 30%. Comparisons with similar observations from the solar eclipse of 11 August 1999 revealed quite different horizontal distribution of the depletion which is assumed to be related to differences in the meridional thermospheric wind system.