Numerical Magnetohydrodynamic Experiments for Testing the Physical Mechanisms of Coronal Mass Ejections Acceleration |
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| Authors: | S T WU T X Zhang E Tandberg-Hanssen Yang Liu Xueshang Feng Arjun Tan |
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| Institution: | (1) Center for Space Plasma and Aeronomic Research, University of Alabama in Huntsville, Huntsville, AL, 35899, U.S.A.;(2) Department of Mechanical and Aerospace Engineering, University of Alabama in Huntsville, Huntsville, AL, 35899, U.S.A.;(3) W. W. Hansen Experimental Physics Laboratory, Stanford University, Stanford, CA, 94305-4085, U.S.A.;(4) Laboratory for Space Weather, Center for Space Science and Applied Research, Chinese Academy of Sciences, Beijing, 100080, P.R. China;(5) Department of Physics, Alabama A & M University, Normal, AL, 35762, U.S.A. |
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| Abstract: | Analysis of observations from both space-borne (LASCO/SOHO, Skylab and Solar Maximum Mission) and ground-based (Mauna Loa Observatory) instruments show that there are two types of coronal mass ejections (CMEs), fast CMEs and slow CMEs. Fast CMEs start with a high initial speed, which remains more or less constant, while slow CMEs start with a low initial speed, but show a gradual acceleration. To explain the difference between the two types of CMEs, Low and Zhang (2002) proposed that it resulted from a difference in the initial topology of the magnetic fields associated with the underlying quiescent prominences, i.e., a normal prominence configuration will lead to a fast CME, while an inverse quiescent prominence results in a slow CME. In this paper we explore a different scenario to explain the existence of fast and slow CMEs. Postulating only an inverse topology for the quiescent prominences, we show that fast and slow CMEs result from different physical processes responsible for the destabilization of the coronal magnetic field and for the initiation and launching of the CME. We use a 2.5-D, time-dependent streamer and flux-rope magnetohydrodynamic (MHD) model (Wu and Guo, 1997) and investigate three initiation processes, viz. (1) injecting of magnetic flux into the flux-rope, thereby causing an additional Lorentz force that will destabilize the streamer and launch a CME (Wu et al., 1997, 1999); (2) draining of plasma from the flux-rope and triggering a magnetic buoyancy force that causes the flux-rope to lift and launch a CME; and (3) introducing additional heating into the flux-rope, thereby simulating an active-region flux-rope accompanied by a flare to launch a CME. We present 12 numerical tests using these three driving mechanisms either alone or in various combinations. The results show that both fast and slow CMEs can be obtained from an inverse prominence configuration subjected to one or more of these three different initiation processes. |
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