TY - JOUR
T1 - Geomagnetic signatures of sudden ionospheric disturbances during extreme solar radiation events
AU - Dmitriev, A. V.
AU - Yeh, H. C.
N1 - Funding Information:
The authors thank SPIDR NOAA ( http://spidr.ngdc.noaa.gov/spidr/index.jsp ) data resource for providing GOES data about solar radiation fluxes, a team of CELIAS/SEM experiment on the Solar Heliospheric Observatory (SOHO) spacecraft ( http://www.usc.edu/dept/space_science/instrument_pages/sem.htm ) for providing data on EUV fluxes, Kyoto World Data Center for Geomagnetism ( http://swdcwww.kugi.kyoto-u.ac.jp/index.html ) for providing the Dst, ASY/SYM and AE geomagnetic indices, a team of INTERMAGNET data base ( http://www.intermagnet.org/Welcom_e.html ) for convenient access to magnetic records from the worldwide network of magnetometers and a team of Moscow Neutron Monitor ( http://helios.izmiran.rssi.ru/cosray/main.htm ) for providing the GLE data. This work was supported by Grants NSC-94-2811-M-008-039, NSC-95-2811-M-008-020 and NSC96-2923-M-008-001MY3/07-02-92004HHC_a from the National Science Council of Taiwan.
PY - 2008/12
Y1 - 2008/12
N2 - We performed a comparative study of geomagnetic variations, which are associated with sudden ionospheric disturbances (SIDs) caused by great X-class solar flares on July 14, 2000 (Bastille flare) and on October 28, 2003 (Halloween flare). Intense fluxes of solar X-rays and EUV radiation as well as solar energetic particles (SEP) were considered as sources of abundant ionization of the ionosphere and upper atmosphere. Flare-initiated SIDs are revealed as transient geomagnetic variations, which are generated by enhanced electric currents flowing mainly in the bottom-side ionosphere. Those so-called solar flare effects (SFEs) were studied by using of geomagnetic data from INTERMAGNET worldwide network of ground-based magnetometers. In subsolar region the SFE is mainly controlled by the flare X-rays and/or EUV radiation. We found that in the Halloween flare the contribution of X-rays was comparable with the EUV, but in the Bastille flare the EUV flux was dominant. The ionization at high latitudes is generated by the SEP, which energy flux is comparable and even exceeds the solar electromagnetic radiation in that region. It was shown that in the Halloween event the pattern of SFE is formed by a two-vortex current system, which is similar to the quiet day Sq current system. However, during the Bastille flare, the pattern of induced currents is quite different: the northern vortex shifts westward and southern vortex shifts eastward such that the electroject is substantially tilted relative to the geomagnetic equator. From numerical estimations we found that at middle latitudes the SEP-initiated geomagnetic effect becomes comparable with the effects of solar electromagnetic radiation. It was also shown that the SEP contribute to the SFE in the nightside hemisphere. The revealed features of the SEP impact to the ionosphere were found in a good agreement with the theory of energetic particle penetration to the bottom-side magnetosphere.
AB - We performed a comparative study of geomagnetic variations, which are associated with sudden ionospheric disturbances (SIDs) caused by great X-class solar flares on July 14, 2000 (Bastille flare) and on October 28, 2003 (Halloween flare). Intense fluxes of solar X-rays and EUV radiation as well as solar energetic particles (SEP) were considered as sources of abundant ionization of the ionosphere and upper atmosphere. Flare-initiated SIDs are revealed as transient geomagnetic variations, which are generated by enhanced electric currents flowing mainly in the bottom-side ionosphere. Those so-called solar flare effects (SFEs) were studied by using of geomagnetic data from INTERMAGNET worldwide network of ground-based magnetometers. In subsolar region the SFE is mainly controlled by the flare X-rays and/or EUV radiation. We found that in the Halloween flare the contribution of X-rays was comparable with the EUV, but in the Bastille flare the EUV flux was dominant. The ionization at high latitudes is generated by the SEP, which energy flux is comparable and even exceeds the solar electromagnetic radiation in that region. It was shown that in the Halloween event the pattern of SFE is formed by a two-vortex current system, which is similar to the quiet day Sq current system. However, during the Bastille flare, the pattern of induced currents is quite different: the northern vortex shifts westward and southern vortex shifts eastward such that the electroject is substantially tilted relative to the geomagnetic equator. From numerical estimations we found that at middle latitudes the SEP-initiated geomagnetic effect becomes comparable with the effects of solar electromagnetic radiation. It was also shown that the SEP contribute to the SFE in the nightside hemisphere. The revealed features of the SEP impact to the ionosphere were found in a good agreement with the theory of energetic particle penetration to the bottom-side magnetosphere.
KW - Geomagnetic variations
KW - Ionospheric solar flare effects
KW - Solar EUV and X-rays
KW - Solar energetic particles
UR - http://www.scopus.com/inward/record.url?scp=56249131089&partnerID=8YFLogxK
U2 - 10.1016/j.jastp.2008.05.008
DO - 10.1016/j.jastp.2008.05.008
M3 - 期刊論文
AN - SCOPUS:56249131089
SN - 1364-6826
VL - 70
SP - 1971
EP - 1984
JO - Journal of Atmospheric and Solar-Terrestrial Physics
JF - Journal of Atmospheric and Solar-Terrestrial Physics
IS - 15
ER -