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Top-Side Ionosphere Response to Extreme Solar Events

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Top-Side Ionosphere Response to Extreme Solar Events Ann. Geophys., 24, 1469–1477, 2006 www.ann-geophys.net/24/1469/2006/ Annales © European Geosciences Union 2006 Geophysicae 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 Received: 17 August 2005 – Revised: 27 January 2006 – Accepted: 14 Febraury 2006 – Published: 3 July 2006 Part of Special Issue “The 11th International Symposium on Equatorial Aeronomy (ISEA-11), Taipei, May 2005” Abstract. Strong X-flares and solar energetic particle (SEP) particles (SEP), with energies up to hundreds and thousands fluxes are considered as sources of topside ionospheric dis- of MeV. The solar radiation impacts the Earth’s ionosphere turbances observed by the ROCSAT-1/IPEI instrument dur- almost immediately. The impact depends on the spectrum ing the Bastille Day event on 14 July 2000 and the Halloween and contents of the radiation (e.g. Mitra, 1974). event on 28 October–4 November 2003. It was found that The present study regards two outstanding events which within a prestorm period in the dayside ionosphere at alti- occurred in the 23 solar cycle: Bastille Day on 14 July tudes of ∼600 km the ion density increased up to ∼80% in 2000 and the Halloween event on 28 October–4 Novem- response to flare-associated enhancements of the solar X-ray ber 2003. The Bastille Day solar flare on 14 July had a emission. Ionospheric response to the SEP events was re- class X5.7/3B such that the GOES-10 detected the peak in- vealed both at sunlit and nightside hemispheres, where the tensity of 1-min X-ray flux in the 1–8 Angstrom (A)˚ range ion density increased up to ∼40% and 100%, respectively. of about 6·10−4 Watts/m2. The response of the ionospheric We did not find any prominent response of the ion tem- total electron contents (TEC) at sunlit hemisphere to that perature to the X-ray and SEP enhancements. The largest flare is reported to be about 5 TECU (Zhang et al., 2002a; X-ray and SEP impacts were found for the X17 solar flare Liu et al., 2004; Tsurutani et al., 2005), which corresponds on 28 October 2003, which was characterized by the most to an ∼7% increase above the background of ∼69 TECU intense fluxes of solar EUV (Tsurutani et al., 2005) and rela- (1 TECU=1012 electrons/cm−2). The Halloween event was tivistic solar particles (Veselovsky et al., 2004). Solar events accompanied by several extremely strong solar flares. The on 14 July 2000 and 29 October 2003 demonstrate weaker 28 October flare was class X17/4B and the GOES-10 X-ray impacts with respect to their X-ray and SEP intensities. The peak intensity reached up to 18·10−4 Watts/m2. Its iono- weakest ionospheric response is observed for the limb X28 spheric impact, estimated by Tsurutani et al. (2005), and solar flare on 4 November 2003. The topside ionosphere re- Zhang and Xiao (2005) was, respectively, ∼25 TECU and sponse to the extreme solar events is interpreted in terms of 17.6 TECU or ∼30% and ∼21% above the background. The the short-duration impact of the solar electromagnetic radia- X10/3B flare on 29 October (GOES-10 X-ray peak intensity tion and the long-lasting impact of the SEP. of ∼10·10−4 Watts/m2) produced an ∼5 TECU (∼6%) en- Keywords. Ionosphere (Solar radiation and cosmic ray hancement (Tsurutani et al., 2005). The largest in the NOAA ∼ effects: Ionospheric disturbances) – Solar physics, astro- records X28/3B class flare on 4 November caused an 5–7 ∼ physics and astronomy (Energetic particles) ( 5–7%) TECU enhancement (Tsurutani et al., 2005). Note that the X-class of the 4 November 2003 flare was estimated only approximately because of saturation of the GOES X-ray detector in the 1–8 A˚ range. Thus, based on the ionospheric 1 Introduction D-region response, Thomson et al. (2005) estimated for that flare a peak magnitude of X45±5. Extreme solar events are characterized by anomalous en- Two questions arise from above: 1. Why did the relatively hancements of solar hard electromagnetic emission in a fre- weaker flare on 28 October causes the largest TEC enhance- quency range of up to gamma rays and/or of solar energetic ment? 2. Why did the extraordinary flare on 4 November Correspondence to: A. V. Dmitriev produce practically the same TEC enhancement as the rela- ([email protected]) tively moderate flares on 14 July and 29 October? Tsurutani Published by Copernicus GmbH on behalf of the European Geosciences Union. 1470 A. V. Dmitriev et al.: Top-side ionosphere response to extreme solar events ) ) 2 2 1E- 3 1E- 4 m m / / 1E- 4 W W 1E- 5 ( ( 1E- 5 y y 1E- 6 a a r r - - 1E- 7 1E- 6 X X 1 1 - - 1 E+4 1E+ 4 ) ) r r 1 E+3 s 1E+ 3 s 1 E+2 s s 1E+ 2 2 2 1 E+1 m 1E+ 1 m 1 E+0 c c ( ( 1E+ 0 1E- 1 p p I 1E- 1 I 1E- 2 ) ) 3.2 T T ( ( 3.1 g g o o l l 3.1 3.0 3.0 5.8 5.8 5.6 5.6 ) ) 5.4 5.4 D D ( ( 5.2 5.2 g g o o l l 5.0 5.0 4.8 4.8 4.6 4.6 ) ) s s / / 100 0 m m ( ( 0 -50 p p -100 u -100 u V V 90 90 0 0 t t 60 -1 00 6 0 - 100 p s p s K D K D - 200 -2 00 30 30 - 300 -3 00 0 0 11 12 13 14 15 16 27 28 29 30 July 2000 October 2003 Fig. 1. Solar radiation, ionospheric and geomagnetic conditions Fig. 2. The same as in Fig. 1 but for the Halloween event on Figurepreceding 1. the Solar Bastille radiation, Day from 11ionospheric to 15 July 2000 and (from geomagnetic top to Figure27–29 conditions October 2. The 2003. precedingsame as in the Figure Bastille 1 but Day for the Halloween event on October 27-29, 2003. bottom): solar X-ray fluxes with wavelength 0.5–4 A˚ (gray line) fromand 1–8 11A˚ (blackto 15 line); July, integral 2000 fluxes (from of the top interplanetary to bottom): protons solar X-ray fluxes with wavelength 0.5-4 Å (graywith energies line) and>5 MeV 1-8 (black Å (black line), >line);30 MeV integral (dashed line)fluxes and of themagnetic interplanetary emission while protons their gradualwith energies changes are different. >100 MeV (gray line); average temperature (K), density (cm−3), Hence, an additional factor should be considered to explain >5and MeV vertical (black ion drift line), velocity >30 measured MeV in (dashed the top-side line) ionosphere and >100the MeV difference (gray betweenline); average the gradual temperature dynamics of the solar by the ROCSAT-1/ IPEI during sunlit (gray circles) and night- emission and ionospheric response. Tsurutani et al. (2005) -3 (K),side passesdensity (black (cm triangles);), and geomagnetic vertical indicesion drift Kp (dashedvelocity his- measuredsuggested in thatthe thetop long-lasting-side ionosphere TEC variations by the are controlled togram, right axis) and 1-min Dst (solid line). significantly by slow (several hours) electron loss via direct ROCSAT-1/ IPEI during sunlit (gray circles) andrecombination nightside atpasses altitudes (black below 200 triangles); km. geomagnetic indices Kp (dashed histogram, right axis) andAnother 1-min possible Dst (solid factor line). affecting the ionosphere is the so- et al. (2005) revealed that the EUV spectrum of the 28 Octo- lar energetic particles (Reid, 1965). In contrast to the fast ber flare is much different from the other flares, namely in the (∼1 h) flare emission, the SEP enhancements are character- wavelength range 260–340 A˚ that flare is larger by more than ized by gradual variations with characteristic times of several a factor of two. The relatively weak EUV emission of the hours. Moreover, the SEP affect high and middle latitudes limb flare on 4 November is due to a strong center-to-limb ef- around the whole globe. Hence, the ionospheric impact of fect for the EUV (Donnelly, 1976) and, thus, the ionospheric the SEP can be easily distinguished at nightside hemisphere, impact of the limb flare should also be smaller (Zhang et al., where effects from the hard electromagnetic emission are mi- 2002b). nor (e.g. Zhang and Xiao, 2005). One more interesting feature reported by Tsurutani et The solar flares on 14 July 2000 and 28 and 29 October al. (2005) is the remarkable difference between the TEC 2003 generated extremely intensive fluxes of the relativis- enhancements and EUV (as well as X-ray) time profiles. tic SEP, which ground level enhancements (GLE) were mea- Firstly, the TEC peaks are slightly (∼10 min) delayed from sured by neutron monitors, while the limb flare on 4 Novem- the flare peaks. Secondly, the duration of TEC enhancements ber did not produce GLE (Veselovsky et al., 2004). The GLE ∼ is lasting several hours, that is much longer than the flare du- on 28 October was larger (maximum effect of 45%) than ∼ ration. On the other hand, a high correlation was found be- those of the other two GLEs with maximum effects of 35%.
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