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Ann. Geophys., 24, 1469-1477, 2006
www.ann-geophys.net/24/1469/2006/
© European Geosciences Union 2006
Top-side ionosphere response to extreme solar events
A. V. Dmitriev1,2, H.-C. Yeh1, J.-K. Chao1, I. S. Veselovsky2,3, S.-Y. Su1, and C. C. Fu1
1Institute of Space Science, National Central University, Chung-Li, Taiwan
2Skobeltsyn Institute of Nuclear Physics Moscow State University, Moscow, Russia
3Space Research Institute (IKI) Russian Academy of Sciences, Moscow, Russia
Abstract. Strong X-flares and solar energetic particle (SEP) fluxes are considered as
sources of topside ionospheric disturbances observed by the ROCSAT-1/IPEI
instrument during the Bastille Day event on 14 July 2000 and the Halloween
event on 28 October–4 November 2003. It was found that within a prestorm
period in the dayside ionosphere at altitudes of ~600 km the ion
density increased up to ~80% in response to flare-associated
enhancements of the solar X-ray emission. Ionospheric response to the SEP
events was revealed both at sunlit and nightside hemispheres, where the ion
density increased up to ~40% and 100%, respectively. We did not
find any prominent response of the ion temperature to the X-ray and SEP
enhancements. The largest X-ray and SEP impacts were found for the X17 solar
flare on 28 October 2003, which was characterized by the most intense
fluxes of solar EUV (Tsurutani et al., 2005) and relativistic solar
particles (Veselovsky et al., 2004). Solar events on 14 July 2000 and
29 October 2003 demonstrate weaker impacts with respect to their X-ray and
SEP intensities. The weakest ionospheric response is observed for the limb
X28 solar flare on 4 November 2003. The topside ionosphere response to the
extreme solar events is interpreted in terms of the short-duration impact of the
solar electromagnetic radiation and the long-lasting impact of the SEP.
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