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福布斯下降(Forbush decrease,FD)是银河宇宙线(galactic cosmic rays,GCRs)受短期剧烈太阳活动调制的重要现象之一.本文设GCRs进入由行星际日冕物质抛射(interplanetary coronal mass ejection,ICME)及其前沿激波共同形成的扰动区时,其径向扩散系数rr受抑制变为(r)rr(0 (r) 1),且抑制强度与粒子位置处的太阳风等离子体速度正相关.对任意时刻的扰动区,抑制系数(r)在激波处最小为(rsh)),并按指数规律增大,在ICME尾部归一.CME爆发时,(rsh))取全局最小值m.在扰动区向日球层外传播的过程中,(rsh))逐步恢复为1.在此基础上,根据GOES和ACE卫星观测确定模型参数,用一维随机微分方程描述GCRs在日球层内的传播,并采用倒向随机方法模拟了一个由独立Halo ICME调制GCRs引起的2005年5月15日FD事件.计算所得地面中子通量的主相、恢复相及其在CME到达地球前的增加过程,均与Oulu中子探测器观测结果一致.Forbush decrease (FD) event is one of the most important short-term modulations of galactic cosmic rays (GCRs) caused by intense solar activities such as interplanetary coronal mass ejection (ICME). The modulation mechanisms of GCRs by the disturbed interplanetary magnetic fields (IMF) of ICME and the accompanying forward interplanetary shock (IP) are not clear yet. In this work, we present a one-dimensional dynamic model of the GCR barrier driven by ICME. In our model, the time dependent radial diffusion coefficient rr of GCRs is depressed to be (r)rr (0 (r) 1) as they run into the disturbed IMF. The scale factor (r) is inversely proportional to the local solar wind speed away from the Sun. Within the disturbed area at any time, (r) increases exponentially from the local minimum (rsh)) at the IP front to 1 at the end of the ICME tail. In addition, (rsh)) switches gradually from its global minimum m at the bursting of the CME to 1 as the shock moving toward the outer boundary of the heliosphere. The geometrical and dynamic parameters of the ICME and IP are derived from the observations of GOES and ACE satellites. Based on the stochastic transport theory, the one-dimensional backward stochastic differential equation (SDE) method is adopted to simulate the transport of GCRs modulated by single halo ICME. The evolution of the neutron flux at the ground is calculated according to the recently reported proton-neutron yield function. As an example, the FD event on 15 May 2005, caused by the CME event bursting on 13 May 2005, is studied and simulated. The results show that the calculated neutron flux evolution, including not only the main and recovery phases, but also the pre-enhancement before the arriving of the CME at the Earth, is consistent with the observation of Oulu neutron monitor. According to the trajectories of GCRs, it can be found that, the per-enhancement of the neutron flux is a result of the scattering by the forward IP passing 1 AU. Before the IP reaches the switch cutoff Rc, GCRs are evidently confined in the sheath between the IP and CME. After that, the GCRs will stay for longer time in the magnetic cloud of the ICME as a result of the damping of IP strength. The parameterzed one-dimensional GCRs modulation model and the SDE method, as have been confirmed by the neutron monitor observation on the Earth, can be used further to calculate and predict the GCRs fluxes of other places, such as the Mars, in the heliosphere.
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Keywords:
- interplanetary coronal mass ejection /
- Forbush decrease /
- backward stochastic differential method /
- neutron flux
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[2] Blasi P 2013 Astron. Astrophys. Rev. 21 70
[3] Bothmer V, Daglis I A 2007 Space Weather- Physics and Effects (Berlin: Springer) pp103130
[4] Le G M 2002 Ph. D. Dissertation (Beijing: Chinese Academy of Sciences) (in Chinese) [乐贵明2002 博士学位论文(北京: 中国科学院空间科学与应用研究中心)]
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[11] Zhao L L, Zhang H 2016 Astrophys. J. 827 13
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[21] Gil A, Iskra K, Modzelewska R, Alania M V 2005 Adv.Space Res. 35 687
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[27] Dunzlaff P, Strauss R D, Potgieter M S 2015 Comput.Phys. Commun. 192 156
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[34] Parker E N 1965 Planet. Space Sci. 13 9
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[38] Nishida A 1982 J. Geophys. Res. 87 6003
[39] Richardson I G, Cane H V 2010 Sol. Phys. 264 189
[40] Thomas B T, Gall R 1984 J. Geophys. Res. 89 2991
[41] Wang C, Du D, Richardson J D, Liu Y 2005 Proceedings of the Solar Wind 11/SOHO16, Connecting Sun and Heliosphere Conference (ESA SP-592) Whistler,Canada, June 1217, 2005 p781
[42] Verma P L, Patel N K, Prajapati M 2014 J. Phys. Conf.Ser. 511 012057
[43] Ahluwalia H S, Alania M V, Wawrzynczak A, Ygbuhay R C, Fikani M M 2014 Sol. Phys. 289 1763
[44] Mishev A L, Usoskin I G, Kovalstov G A 2013 J. Geophys.Res. 118 2783
[45] Mangeard P S, Ruffolo D, Saiz A, Madlee S, Nutaro T 2016 J. Geophys. Res. 121 7435
[46] Papailiou M, Mavromichalaki H, Belov A, Eroshenko E,Yanke V 2012 Sol. Phys. 276 337
[47] Feng L, Inhester B, Wei Y, Gan W Q, Zhang T L, Wang M Y 2012 Astrophys. J. 751 18
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[1] Rossi B 1964 Cosmic Rays (New York: McGraw-Hill) pp110
[2] Blasi P 2013 Astron. Astrophys. Rev. 21 70
[3] Bothmer V, Daglis I A 2007 Space Weather- Physics and Effects (Berlin: Springer) pp103130
[4] Le G M 2002 Ph. D. Dissertation (Beijing: Chinese Academy of Sciences) (in Chinese) [乐贵明2002 博士学位论文(北京: 中国科学院空间科学与应用研究中心)]
[5] Potgieter M S 2013 Living Rev. Sol. Phys. 10 3
[6] Guo W J, Zhu B Y 1990 Chin. J. Spac. Sci. 10 247 (in Chinese) [郭维吉, 朱邦耀1990 空间科学学报10 247]
[7] Kharayat H, Prasad L, Mathpal R, Garia S, Bhatt B 2016 Sol. Phys. 291 603
[8] Cane H V 2000 Space Sci. Rev. 93 55
[9] Belov A, Abunin A, Abunina M, Eroshenko E, Oleneva V, Yanke V, Papaioannou A, Mavromichalaki H, Gopalswamy N, Yashiro S 2014 Sol. Phys. 289 3949
[10] Yu X X, Lu H, Le G M, Shi F 2010 Sol. Phys. 263 223
[11] Zhao L L, Zhang H 2016 Astrophys. J. 827 13
[12] Le G M, Han Y B 2005 Acta Phys. Sin. 54 467 (in Chinese)[乐贵明, 韩延本2005 物理学报54 467]
[13] Dorman L I 2005 Ann. Geophys. 23 2997
[14] Huang Y L, Fu Y F, Chen J M, Huang G S, Liu X N 2015 Res. Astron. Astrophys. 16 82 (in Chinese) [黄寅亮, 傅元芬, 陈济民, 黄更生, 刘小宁2015 天体物理学报16 82]
[15] Lockwood J A 1971 Space Sci. Rev. 12 658
[16] Jokipii J R, Kota J 1986 J. Geophys. Res. 91 2885
[17] Li G, Webb G M, Roux J A L, Zank G P, Wiedenbeck M E 2007 Numerical Modeling of Space Plasma Flows 385 31
[18] Li G, Webb G M, Roux J A L, Wiedenbeck M, Florinski V, Zank G P 2009 Proceedings of the 31st ICRC Td, Poland, July 715, 2009
[19] Fisk L A 1971 J. Geophys. Res. 76 221
[20] Hattingh M, Burger R A, Potgieter M S, Haasbroeket L J 1997 Adv. Space Res. 19 893
[21] Gil A, Iskra K, Modzelewska R, Alania M V 2005 Adv.Space Res. 35 687
[22] Strauss R D, Potgieter M S, Bsching I, Kopp A 2012 Astrophys. Space Sci. 339 223
[23] Gleeson L 1968 Astrophys. J. 154 1011
[24] Caballero-Lopez R A, Moraal H, Mcdonald F B 2004 J.Geophys. Res. 109 361
[25] Usoskin I G, Bazilevskaya G A, Kovaltsov G A 2011 J.Geophys. Res. 116 1
[26] Usoskin I G, Kovaltsov G A, Adriani O, Barbarino G C,Bazilevskaya G A, Bellotti R 2015 Adv. Space Res. 55 2940
[27] Dunzlaff P, Strauss R D, Potgieter M S 2015 Comput.Phys. Commun. 192 156
[28] Zhang M 1999 Astrophys. J. 513 409
[29] Wawrzynczak A, Modzelewska R, Gil A 2015 J. Phys.Conf. Ser. 574 012078
[30] Pei C, Bieber J W, Breech B, Burger R A, Clem J,Matthaeus W H 2010 J. Geophys. Res. 115 333
[31] Luo X, Zhang M, Rassoul H K, Pogorelov N V 2011 Astrophys. J. 730 13
[32] Luo X, Zhang M, Feng X, Mendoza-Torres J E 2013 J.Geophys. Res. 118 7517
[33] Bobik P, Boella G, Boschini M J, Consolandi C, Della Torre S, Gervasi M, Grandi D, Kudela K, Pensotti S,Rancoita P G, Tacconi M 2012 Astrophys. J. 745 132
[34] Parker E N 1965 Planet. Space Sci. 13 9
[35] Schuss Z 1980 Theory and Applications of Stochastic Differential Equations (New York: John Wiley) pp1095
[36] Wiedenbeck M E, Davis A J, Leske R A, Binna W R,Cohen C M S, Cummings A C, de Nolfo G, Israel M H,Labrador A W, Mewaldt R A, Scott L M, Stone E C,von Rosenvinge T T 2005 Proceedings of the 29th International Cosmic Ray Conference Pune, India, August 310, 2005 p227
[37] Chih P P, Lee M A 1986 J. Geophys. Res. 91 2903
[38] Nishida A 1982 J. Geophys. Res. 87 6003
[39] Richardson I G, Cane H V 2010 Sol. Phys. 264 189
[40] Thomas B T, Gall R 1984 J. Geophys. Res. 89 2991
[41] Wang C, Du D, Richardson J D, Liu Y 2005 Proceedings of the Solar Wind 11/SOHO16, Connecting Sun and Heliosphere Conference (ESA SP-592) Whistler,Canada, June 1217, 2005 p781
[42] Verma P L, Patel N K, Prajapati M 2014 J. Phys. Conf.Ser. 511 012057
[43] Ahluwalia H S, Alania M V, Wawrzynczak A, Ygbuhay R C, Fikani M M 2014 Sol. Phys. 289 1763
[44] Mishev A L, Usoskin I G, Kovalstov G A 2013 J. Geophys.Res. 118 2783
[45] Mangeard P S, Ruffolo D, Saiz A, Madlee S, Nutaro T 2016 J. Geophys. Res. 121 7435
[46] Papailiou M, Mavromichalaki H, Belov A, Eroshenko E,Yanke V 2012 Sol. Phys. 276 337
[47] Feng L, Inhester B, Wei Y, Gan W Q, Zhang T L, Wang M Y 2012 Astrophys. J. 751 18
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