| 2009 Top |
| 12. | Ming Xiong, Huinan Zheng, and Shui Wang, Magnetohydrodynamic simulation of the interaction between two interplanetary magnetic clouds and its consequent geoeffectiveness: 2. Oblique collision, J. Geophys. Res. - Space Phys., 114, A11101, doi:10.1029/2009JA014079, 2009-11. [ (2.25MB)] | Abstract. The numerical studies of the interplanetary coupling between multiple magnetic clouds (MCs) are continued by a 2.5-dimensional ideal magnetohydrodynamic (MHD) model in the heliospheric meridional plane. The interplanetary direct collision (DC) / oblique collision (OC) between both MCs results from their same/different initial propagation orientations. Here the OC is explored in contrast to the results of the DC (Xiong et al., 2007). Both the slow MC1 and fast MC2 are consequently injected from the different heliospheric latitudes to form a compound stream during the interplanetary propagation. The MC1 and MC2 undergo contrary deflections during the process of oblique collision. Their deflection angles of $|\delta \theta_1|$ and $|\delta \theta_2|$ continuously increase until both MC-driven shock fronts are merged into a stronger compound one. The $|\delta \theta_1|$, $|\delta \theta_2|$, and total deflection angle $\Delta \theta$ ($\Delta \theta = |\delta \theta_1| + |\delta \theta_2|$) reach their corresponding maxima when the initial eruptions of both MCs are at an appropriate angular difference. Moreover, with the increase of MC2's initial speed, the OC becomes more intense, and the enhancement of $\delta \theta_1$ is much more sensitive to $\delta \theta_2$. The $|\delta\theta_1|$ is generally far less than the $|\delta\theta_2|$, and the unusual case of $|\delta\theta_1|\simeq|\delta\theta_2|$ only occurs for an extremely violent OC. But because of the elasticity of the MC body to buffer the collision, this deflection would gradually approach an asymptotic degree. As a result, the opposite deflection between the two MCs, together with the inherent magnetic elasticity of each MC, could efficiently relieve the external compression for the OC in the interplanetary space. Such deflection effect for the OC case is essentially absent for the DC case. Therefore, besides the magnetic elasticity, magnetic helicity, and reciprocal compression, the deflection due to the OC should be considered for the evolution and ensuing geoeffectiveness of interplanetary interaction among successive coronal mass ejections (CMEs).
This work was supported by the National Natural Science Foundation of China (40774077), the National Key Basic Research Special Foundation of China (2006CB806304). M. Xiong was also supported by the China Postdoctoral Science Foundation (both special and general sponsorships) and the K. C.Wong Education Foundation of Hong Kong. |
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| 11. | Z. P. Su, Ming Xiong, Huinan Zheng, and S. Wang, Propagation of interplanetary shock and its consequent geoeffectiveness, Chinese J. Geophys., 52, 2009-03. [(1.76MB)] | |
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| 10. | Z. P. Su, Huinan Zheng, and Ming Xiong, Dynamic evolution of outer radiation belt electrons due to whistler-mode chorus, Chinese Phys. Lett., 26, 039401, 2009-03. [(1.55MB)] | |
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| 9. | Ming Xiong, Zhong Peng, Youqiu Hu, and Huinan Zheng, Response of the Earth's Magnetosphere and Ionosphere to Solar Wind Driver and Ionosphere Load: Results of Global MHD Simulations, Chinese Phys. Lett., 26, 015202, 2009-01. [(221.2KB)] | Abstract. Three-dimensional global magnetohydrodynamic simulations of the solar wind-magnetosphere-ionosphere system are carried out to explore the dependence of the magnetospheric reconnection voltage, the ionospheric transpolar potential, and the field aligned currents (FACs) on the solar wind driver and ionosphere load for the cases with pure southward interplanetary magnetic field (IMF). It is shown that the reconnection voltage and the transpolar potential increase monotonically with decreasing Pedersen conductance (ΣP), increasing southward IMF strength (Bs) and solar wind speed (vsw). Moreover, both regions 1 and 2 FACs increase when Bs and vsw increase, whereas the two currents behave differently in response to ΣP. As ΣP increases, the region 1 FAC increases monotonically, but region 2 FAC shows a non-monotonic response to the increase of ΣP: it first increases in the range of (0,5) Siemens and then decreases for ΣP > 5 Siemens.
Supported by the National Natural Science Foundation of China under Grant Nos 40831060, 40621003 and 40774077, the China Postdoctoral Science Foundation (20070420725), and K. C. Wong Education Foundation of Hong Kong. |
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| 2008 Top |
| 8. | Huinan Zheng, Z. P. Su, and Ming Xiong, Pitch angle distribution evolution of energetic electrons by whistler-mode chorus, Chinese Phys. Lett., 25, 3515-3518, 2008-09. [(531.6KB)] | |
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| 2007 Top |
| 7. | Ming Xiong, Numerical MHD Simulation of the Dynamics and Geoeffectiveness of Some Interplanetary Compound Structures, Ph.D Dissertation, , 2007-06. [(21.81MB)] | Abstract. The interplanetary (IP) space is a key node of the cause-effect chain for the space weather, as a pivot linking the Sun and the Earth. “Multiple magnetic cloud” (Multi-MC) and “shock overtaking MC” are two particular types of IP compound structures, and are both proved by observations of spacecraft and ground-based observatories to be two important IP sources of large geomagnetic storms. A comprehensive investigation of “Multi-MC” and “shock overtaking MC” is carried out by numerical MHD simulation. It is focused on dynamics and ensuing geoeffectiveness, closely combined with spacecraft observations. The main conclusions can be summarized as the following three points:
1. The construction of a heliospheric numerical magnetohydrodynamic code for space weather prediction of interplanetary MC disturbances
In order to simulate the physical process of shock entering MC, a source code is constructed on basis of a compound scheme of shock-capturing methods. The numerical model can numerically solve the mathematical problem of interaction between a sharp discontinuity and a complicated smooth structure, guarantee the divergence-free condition of magnetic field in numerical computation. Thus it provides an indispensable premise and powerful platform for the research of physical problems.
2. The numerical simulation of the “direct collision” and “oblique collision” for “shock overtaking MC”
An incidental shock first catches up with a preceding MC, then penetrates through the MC, and finally merges with the MC-driven shock into a stronger compound shock. The MC body is highly compressed by the shock front along its normal. After the shock passage, the previously compressed MC body is gradually restored to an oblate morphology under the action of its inherent magnetic elasticity. The compression and rotation of the magnetic field serve as an efficient mechanism to cause a large geomagnetic storm. Moreover, when a shock penetrates an MC at the different depth, the resulting geomagnetic storm is also different. Regardless of the shock orientation, the shock penetration location regarding the maximum geoeffectiveness is right at MC core on the condition of very strong shock intensity. Quantified by the Dst index, the simulation results reveal that the geoeffectiveness of an individual MC is largely enhanced with 80% increment in maximum by an incidental shock. Furthermore, it is found that the oblique penetration of a shock through an MC leads to the MC deflection. The opposite deflections of MC body and shock aphelion in the MC-shock oblique collision occur simultaneously through the process of shock penetrating MC. The dependence of such deflection on the initial shock intensity and orientation is also explored. An appropriate angular difference between the initial eruption of an MC and an overtaking shock leads to the maximum deflection of the MC body. The larger the shock intensity is, the greater is the deflection angle. Therefore, the interaction of MCs with other disturbances could be a cause of deflected propagation of interplanetary coronal mass ejection (ICME).
3. The numerical simulation of a Multi-MC formed by the “direct collision” of two MCs
Both slow preceding MC (MC1) and fast following MC (MC2) are initially launched along the heliospheric equator, one after another with different time interval. The coupling of two MCs involves the comprehensive interaction among the MC1 body, MC1-driven shock, MC2 body, and MC2-driven shock. After the passage of MC2-driven shock front, magnetic field lines in MC1 medium previously compressed by MC2-driven shock are prevented from being restored by the MC2 body pushing. As the evolution proceeds, the MC1 body suffers from the larger and larger compression, and its original vulnerable magnetic elasticity becomes stiffer and stiffer. So there exists a maximum compressibility of the Multi-MC when the accumulated elasticity can balance the external compression. This cutoff limit of compressibility mainly decides the maximally available geoeffectiveness of a Multi-MC, because the geoeffectiveness enhancement of MCs interacting is ascribed to the compression. The intense compression accompanying the southward magnetic field (Bs) event is responsible for the geoeffectiveness enhancement of “Multi-MC” and “shock overtaking MC”. The magnetic elasticity, magnetic helicity of each MC, and compression between each other are the key physical factors for the formation, propagation, evolution, and resulting geoeffectiveness of the interplanetary Multi-MC. |
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| 6. | Ming Xiong, Huinan Zheng, S. T. Wu, Yuming Wang, and Shui Wang, Magnetohydrodynamic simulation of the interaction between two interplanetary magnetic clouds and its consequent geoeffectiveness, J. Geophys. Res. - Space Phys., 112, A11103, doi:10.1029/2007JA012320, 2007-05. [(12.95MB)] | Abstract. Numerical studies of the interplanetary ``multiple magnetic clouds (Multi-MC)'' are performed by a 2.5-dimensional ideal magnetohydrodynamic (MHD) model in the heliospheric meridional plane. Both slow MC1 and fast MC2 are initially emerged along the heliospheric equator, one after another with different time intervals. The coupling of two MCs could be considered as the comprehensive interaction between two systems, each comprising of an MC body and its driven shock. The MC2-driven shock and MC2 body are successively involved into interaction with MC1 body. The momentum is transferred from MC2 to MC1. After the passage of MC2-driven shock front, magnetic field lines in MC1 medium previously compressed by MC2-driven shock are prevented from being restored by the MC2 body pushing. MC1 body undergoes the most violent compression from the ambient solar wind ahead, continuous penetration of MC2-driven shock through MC1 body, and persistent pushing of MC2 body at MC1 tail boundary. As the evolution proceeds, the MC1 body suffers from larger and larger compression, and its original vulnerable magnetic elasticity becomes stiffer and stiffer. So there exists a maximum compressibility of Multi-MC when the accumulated elasticity can balance the external compression. This cutoff limit of compressibility mainly decides the maximally available geoeffectiveness of Multi- MC because the geoeffectiveness enhancement of MCs interacting is ascribed to the compression. Particularly, the greatest geoeffectiveness is excited among all combinations of each MC helicity, if magnetic field lines in the interacting region of Multi-MC are all southward. Multi-MC completes its final evolutionary stage when the MC2-driven shock is merged with MC1-driven shock into a stronger compound shock. With respect to Multi-MC geoeffectiveness, the evolution stage is a dominant factor, whereas the collision intensity is a subordinate one. The magnetic elasticity, magnetic helicity of each MC, and compression between each other are the key physical factors for the formation, propagation, evolution, and resulting geoeffectiveness of interplanetary Multi-MC.
This work was supported by the National Key Basic Research Special Foundation of China (2006CB806304), the Chinese Academy of Sciences grant KZCX3-SW-144, the National Natural Science Foundation of China (40336052, 40404014, 40525014, 40574063, and 40774077), and the Chinese Academy of Sciences (startup fund). S. T. Wu was supported by an NSF grant (ATM03-16115). |
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| 2006 Top |
| 5. | Ming Xiong, Huinan Zheng, Yuming Wang, and Shui Wang, Magnetohydrodynamic simulation of the interaction between interplanetary strong shock and magnetic cloud and its consequent geoeffectiveness: 2. Oblique collision, J. Geophys. Res. - Space Phys., 111, A11102, doi:10.1029/2006JA011901, 2006-11. [(4.51MB)] | Abstract. Numerical studies of the interplanetary ``shock overtaking magnetic cloud (MC)'' event are continued by a 2.5-dimensional magnetohydrodynamic (MHD) model in heliospheric meridional plane. Interplanetary direct collision (DC)/oblique collision (OC) between an MC and a shock results from their same/different initial propagation orientations. For radially erupted MC and shock in solar corona, the orientations are only determined respectively by their heliographic locations. OC is investigated in contrast with the results in DC (Xiong, 2006). The shock front behaves as a smooth arc. The cannibalized part of MC is highly compressed by the shock front along its normal. As the shock propagates gradually into the preceding MC body, the most violent interaction is transferred sideways with an accompanying significant narrowing of the MC's angular width. The opposite deflections of MC body and shock aphelion in OC occur simultaneously through the process of the shock penetrating the MC. After the shock's passage, the MC is restored to its oblate morphology. With the decrease of MC-shock commencement interval, the shock front at 1 AU traverses MC body and is responsible for the same change trend of the latitude of the greatest geoeffectiveness of MC-shock compound. Regardless of shock orientation, shock penetration location regarding the maximum geoeffectiveness is right at MC core on the condition of very strong shock intensity. An appropriate angular difference between the initial eruption of an MC and an overtaking shock leads to the maximum deflection of the MC body. The larger the shock intensity is, the greater is the deflection angle. The interaction of MCs with other disturbances could be a cause of deflected propagation of interplanetary coronal mass ejection (ICME).
This work was supported by the National Natural Science Foundation of China (40336052, 40404014, 40525014, and 40574063), the Chinese Academy of Sciences (startup fund), and the National Key Basic Research Special Foundation of China (2006CB806304). M. Xiong was also supported by Innovative Fund of University of Science and Technology of China for Graduate Students (KD2005030). |
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| 4. | Ming Xiong, Huinan Zheng, Yuming Wang, and Shui Wang, Magnetohydrodynamic simulation of the interaction between interplanetary strong shock and magnetic cloud and its consequent geoeffectiveness, J. Geophys. Res. - Space Phys., 111, A08105, doi:10.1029/2005JA011593, 2006-08. [(4.88MB)] | Abstract. Numerical studies have been performed to interpret the observed ``shock overtaking magnetic cloud (MC)'' event by a 2.5 dimensional magnetohydrodynamic (MHD) model in the heliospheric meridional plane. Results of an individual MC simulation show that the MC travels with a constant bulk flow speed. The MC is injected with a very strong inherent magnetic field over that in the ambient flow and expands rapidly in size initially. Consequently, the diameter of the MC increases in an asymptotic speed while its angular width contracts gradually. Meanwhile, simulations of MC-shock interaction are also presented, in which both a typical MC and a strong fast shock emerge from the inner boundary and propagate along the heliospheric equator, separated by an appropriate interval. The results show that the shock first catches up with the preceding MC, then penetrates through the MC, and finally merges with the MC-driven shock into a stronger compound shock. The morphologies of shock front in interplanetary space and MC body behave as a central concave and a smooth arc, respectively. The compression and rotation of the magnetic field serve as an efficient mechanism to cause a large geomagnetic storm. The MC is highly compressed by the overtaking shock. Contrarily, the transport time of the incidental shock influenced by the MC depends on the interval between their commencements. Maximum geoeffectiveness results from when the shock enters the core of preceding MC, which is also substantiated to some extent by a corresponding simplified analytic model. Quantified by the $Dst$ index, the specific result is that the geoeffectiveness of an individual MC is largely enhanced with 80\% increment in maximum by an incidental shock.
This work was supported by the National Natural Science Foundation of China (40274050, 40404014, 40336052 and 40525014), and the Chinese Academy of Sciences (startup fund). M. Xiong was also supported by Innovative Fund of University of Science and Technology of China for Graduate Students (KD2005030). |
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| 2005 Top |
| 3. | Ming Xiong, Hui-Nan Zheng, Yu-Ming Wang, Xiang-Rong Fu, Shui Wang, and Xian-Kang Dou, A numerical simulation on the solar-terrestrial transit time of successive CMEs during November 4-5, 1998, Chinese J. Geophys., 48, 805-813, 2005-07. [(382.4KB), (596KB)] | Abstract. The solar-terrestrial transit process of three successive coronal mass ejections (CMEs) during November 4-5, 1998 has been investigated numerically in one-dimensional spherical geometry. These CMEs interact with each other while they are propagating in interplanetary space and finally form a “Complex Ejecta”. A Harten’s total variation diminishing (TVD) scheme is applied to solve magnetohydrodynamic (MHD) equations numerically, starting from an ambient solar wind equilibrium, with appropriate dimensionless gravity parameter, plasma beta, and gas polytropic index . The equilibrium is consistent in solar wind speed vr, proton number density Np, and the ratio of proton thermal pressure to magnetic pressure with the observation of ACE spacecraft at Lagrange point (L1). Merely velocity pulse is introduced in the numerical computation, whose amplitude and duration are determined by observation data of Lasco/C2, GOES, LEAR combined with CME’s “Cone Model” proposed by Michalek et al. The results show that the differences of two shock arrival times (SATs) between the numerical calculation and ACE observation are 3 and 4 hours respectively. Therefore the numerical model proposed in this paper can estimate SAT and rough shock intensity formed by successive CMEs evolving in interplanetary space and suggests a potential application in SAT prediction for space weather.
This work was supported by the National Natural Science Foundation of China (40274050, 40336052, 40404014), the Ministry of Science and Technology of China (NKBRSF G2000078405) and the Chinese Academy of Sciences (KZCX2-SW-136). The authors also acknowledge the use of observation data from SOHO, ACE, GOES spacecrafts and LEAR observatory with gratitude. |
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| 2. | X. H. Xue, Yuming Wang, P. Z. Ye, S. Wang, and M. Xiong, Analysis on the interplanetary causes of the great magnetic storms in solar maximum (2000–2001), Planet. & Space Sci., 53, 443-457, 2005-03. [(2.48MB)] | |
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| 2003 Top |
| 1. | Y. M. Wang, P. Z. Ye, S. Wang, and M. Xiong, Theoretical analysis on the geoeffectiveness of a shock overtaking a preceding magnetic cloud, Sol. Phys., 216, 295-310, 2003-06. [(268KB)] | |
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