Yufen Zhou

Three‐dimensional MHD simulation of two coronal mass ejections' propagation and interaction using a successive magnetized plasma blobs model

A three-dimensional (3-D), time-dependent, numerical magnetohydrodynamic (MHD) model is used to investigate the evolution and interaction of two coronal mass ejections (CMEs) in the nonhomogeneous ambient solar wind. The background solar wind is constructed on the basis of the self-consistent source surface with observed line of sight of magnetic field and density from the source surface of 2.5 R(s) to Earths orbit (215 R(s)) and beyond. The two successive CMEs occurring on 28 March 2001 and forming a multiple magnetic cloud in interplanetary space are chosen as a test case, in which they are simulated by means of a two high-density, high-velocity, and high-temperature magnetized plasma blobs model, and are successively ejected into the nonhomogeneous background solar wind medium along different initial launch directions. The dynamical propagation and interaction of the two CMEs between 2.5 and 220 R(s) are investigated. Our simulation results show that, although the two CMEs are separated by 10 h, the second CME is able to overtake the first one and cause compound interactions and an obvious acceleration of the shock. At the L1 point near Earth the two resultant magnetic clouds in our simulation are consistent with the observations by ACE. In this validation study we find that this 3-D MHD model, with the self-consistent source surface as the initial boundary condition and the magnetized plasma blob as the CME model, is able to reproduce and explain some of the general characters of the multiple magnetic clouds observed by satellite.

Using a 3‐D spherical plasmoid to interpret the Sun‐to‐Earth propagation of the 4 November 1997 coronal mass ejection event

We present the time-dependent propagation of a Sun-Earth connection event that occurred on 4 November 1997 using a three-dimensional (3-D) numerical magnetohydrodynamics (MHD) simulation. A global steady state solar wind for this event is obtained by a 3-D SIP-CESE MHD model with Parkers 1-D solar wind solution and measured photospheric magnetic fields as the initial values. Then, superposed on the quiet background solar wind, a spherical plasmoid is used to mimic the 4 November 1997 coronal mass ejection (CME) event. The CME is assumed to arise from the evolution of a spheromak magnetic structure with high-speed, high-pressure, and high-plasma-density plasmoid near the Sun. Moreover, the axis of the initial simulated CME is put at S14W34 to conform to the observed location of this flare/ CME event. The result has provided us with a relatively satisfactory comparison with the Wind spacecraft observations, such as southward interplanetary magnetic field and large-scale smooth rotation of the magnetic field associated with the CME.

MHD numerical study of the latitudinal deflection of coronal mass ejection

In this paper, we analyze and quantitatively study the deflection of coronal mass ejection (CME) in the latitudinal direction during its propagation from the Corona to interplanetary (IP) space using a three-dimensional (3-D) numerical magnetohydrodynamics (MHD) simulation. To this end, 12 May 1997 CME event during the Carrington rotation 1922 is selected. First, we try to reproduce the physical properties for this halo CME event observed by the WIND spacecraft. Then, we study the deflection of CME, and quantify the effect of the background magnetic field and the initiation parameters (such as the initial magnetic polarity and the parameters of the CME model) on the latitudinal deflection of CMEs. The simulations show that the initial magnetic polarity substantially affects the evolution of CMEs. The “parallel” CMEs (with the CMEs initial magnetic field parallel to that of the ambient field) originating from high latitude show a clear Equatorward deflection at the beginning and then propagate almost parallel to heliospheric current sheet and the “antiparallel” CMEs (with the CMEs initial magnetic field opposite to that of the ambient field) deflect toward the pole. Our results demonstrate that the latitudinal deflection extent of the “parallel” CMEs is mainly controlled not only by the background magnetic field strength but also by the initial magnetic field strength of the CMEs. There is an anticorrelation between the latitudinal deflection extent and the CME average transit speed and the energy ratio Ecme/Esw.

SIP-CESE MHD model of solar wind with adaptive mesh refinement of hexahedral meshes

Solar-interplanetary space involves many features, such as discontinuities and heliospheric current sheet, with spatial scales many orders of magnitude smaller than the system size. The scalable, massively parallel, block-based, adaptive-mesh refinement (AMR) promises to resolve different temporal and spatial scales on which solar-wind plasma occurs throughout the vast solar-interplanetary space with even less cells but can generate a good enough resolution. Here, we carry out the adaptive mesh refinement (AMR) implementation of our Solar-Interplanetary space-time conservation element and solution element (CESE) magnetohydrodynamic model (SIP-CESE MHD model) using a six-component grid system (Feng et al., 2007, 2010). The AMR realization of the SIP-CESE MHD model is naturalized directly in hexahedral meshes with the aid of the parallel AMR package PARAMESH available at http://sourceforge.net/projects/paramesh/. At the same time, the topology of the magnetic field expansion factor and the minimum angular separation (at the photosphere) between an open field foot point and its nearest coronal-hole boundary are merged into the model in order to determine the volumetric heating source terms. Our numerical results for the validation study of the solar-wind background of Carrington rotation 2060 show overall good agreements in the solar corona and in interplanetary space with the observations from the Solar and Heliospheric Observatory (SOHO) and spacecraft data from OMNI

Using a 3‐D MHD simulation to interpret propagation and evolution of a coronal mass ejection observed by multiple spacecraft: The 3 April 2010 event

The coronal mass ejection (CME) event on 3 April 2010 is the first fast CME observed by STEREO Sun Earth Connection Coronal and Heliospheric Investigation/Heliospheric Imager for the full Sun-Earth line. Such an event provides us a good opportunity to study the propagation and evolution of CME from the Sun up to 1 AU. In this paper, we study the time-dependent evolution and propagation of this event from the Sun to Earth using the 3-D SIP-CESE (Solar-InterPlanetary Conservation Element and Solution Element) MHD model. The CME is initiated by a simple spherical plasmoid model: a spheromak magnetic structure with high-speed, high-pressure, and high-plasma density plasmoid. The simulation performs a comprehensive study on the CME by comparing the simulation results with STEREO and Wind observations. It is confirmed from the comparison with observations that the MHD model successfully reproduces many features of both the fine solar coronal structure and the typical large-scale structure of the shock propagation and gives the shock arrival time at Earth with an error of similar to 2 h. Then we analyze in detail the several factors affecting the CMEs geo-effectiveness: the CMEs propagation trajectory, span angle, and velocity.

A NEW THREE-DIMENSIONAL SOLAR WIND MODEL IN SPHERICAL COORDINATES WITH A SIX-COMPONENT GRID

In this paper, we introduce a new three-dimensional magnetohydrodynamics numerical model to simulate the steady state ambient solar wind from the solar surface to 215 R-s or beyond, and the model adopts a splitting finite-volume scheme based on a six-component grid system in spherical coordinates. By splitting the magnetohydrodynamics equations into a fluid part and a magnetic part, a finite volume method can be used for the fluid part and a constrained-transport method able to maintain the divergence-free constraint on the magnetic field can be used for the magnetic induction part. This new second-order model in space and time is validated when modeling the large-scale structure of the solar wind. The numerical results for Carrington rotation 2064 show its ability to produce structured solar wind in agreement with observations.

A data-constrained three-dimensional magnetohydrodynamic simulation model for a coronal mass ejection initiation

In this study, we present a three-dimensional magnetohydrodynamic model based on an observed eruptive twisted flux rope (sigmoid) deduced from solar vector magnetograms. This model is a combination of our two very well tested MHD models: (i) data-driven 3-D magnetohydrodynamic (MHD) active region evolution (MHD-DARE) model for the reconstruction of the observed flux rope and (ii) 3-D MHD global coronal-heliosphere evolution (MHD-GCHE) model to track the propagation of the observed flux rope. The 6 September 2011, AR11283, event is used to test this model. First, the formation of the flux rope (sigmoid) from AR11283 is reproduced by the MHD-DARE model with input from the measured vector magnetograms given by Solar Dynamics Observatory/Helioseismic and Magnetic Imager. Second, these results are used as the initial boundary condition for our MHD-GCHE model for the initiation of a coronal mass ejection (CME) as observed. The model output indicates that the flux rope resulting from MHD-DARE produces the physical properties of a CME, and the morphology resembles the observations made by STEREO/COR-1.

Numerical study of the propagation characteristics of coronal mass ejections in a structured ambient solar wind: THE CME PROPAGATION CHARACTERISTICS

Using a three-dimensional (3-D) magnetohydrodynamics (MHD) model, we analyze and study the propagation characteristics of coronal mass ejections (CMEs) launched at different positions in a realistic structured ambient solar wind. Here the ambient solar wind structure during the Carrington rotation 2095 is selected, which is the characteristics of activity rising phase. CMEs with a simple spherical plasmoid structure are initiated at different solar latitudes with respect to the heliospheric current sheet (HCS) and the Earth in the same ambient solar wind. Then, we numerically obtained the evolution process of the CMEs from the Sun to the interplanetary space. When the Earth and the CME launch position are located on the same side of the HCS, the arrival time of the shock at the Earth is faster than that when the Earth and the CME launch position are located on the opposite side of the HCS. The disturbance amplitudes for the same side event are also larger than those for the opposite side event. This may be due to the fact that the HCS between the CME and the Earth for the opposite side event hinders its propagation and weaken it. The CMEs tend to deflect toward the HCS in the latitudinal direction near the corona and then propagate almost parallel to the HCS in the interplanetary space. This deflecting tendency may be caused by the dynamic action of near-Sun magnetic pressure gradient force on the ejected coronal plasma.