Impact of the extraordinary solar activity of October/ November 2003 on the upper boundary of the Earth-ionosphere cavity resonator

A series of dramatic episodes of solar activity occurred in October and November of 2003 known as “Halloween storms”. The hard solar X-ray flux increased by more than two orders of magnitude already between October 18 and 20 and lasted until November 5 while the 10.7 cm radio flux indicating 2-3-fold variations of EUV radiation maximized only on October 28. The time evolution of the disturbances of these two ionization sources was quite different. At the end of October and the beginning of November 2003 two active regions produced a series of extremely energetic solar eruptions. In connection with the flare on October 28, 2003, a coronal mass ejection was emitted at a high speed directly towards the Earth and caused a dramatic Forbush decrease of the galactic cosmic rays (GCR). The large solar storms also caused very large proton fluxes in the final days of October and early November. The fourth largest proton event in the last 40 years occurred in October 28. All these solar electromagnetic and particle radiations have important roles in the ionization of the D-region which forms the upper boundary of the Earth-ionosphere cavity resonator. The effects of these events have been studied by Schumann resonance (SR) parameters measured at Nagycenk, Hungary and in Mitzpe Ramon, Israel. The SR frequency increased simultaneously with the increase of the hard solar X-ray flux in October 18, 2003 and followed it in case of the 1^st and 2^nd E_Z modes both at Nagycenk and in Mitzpe Ramon until November 5, 2003. Neither the increased EUV radiation with maximum on October 28, 2003 nor the huge Forbush-decrease as well as the giant proton events between October 28 and November 4, 2003 left any signature on SR frequencies. SR intensities seem to be largely unaffected by these solar events. These observational results verify the conclusion by Sátori et. al. [2005] that the hard solar X-ray has an important role in modifying the Earth-ionosphere cavity in the range of heights from ~ 90km -100 km.