Photospheric Dynamics of CMEs: Alfvenic Relaxation

Physics

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7513 Coronal Mass Ejections, 7519 Flares, 7524 Magnetic Fields, 7529 Photosphere

Scientific paper

Recently, a new theoretical framework for the physics of solar eruptions has been proposed in which poloidal magnetic flux of existing structures (flux tubes and flux ropes) is increased immediately preceding and during the eruption. A theoretical model of flux-rope type CMEs based on the alternative hypothesis (Chen 1996; Krall et al. 2000) has proven successful in explaining a range of observed CMEs. This scenario corresponds to different generic physics from that of the traditional storage-release paradigm. In the new paradigm, the coronal magnetic field structures are assumed to be connected to the solar dynamo in the convection zone. The magnetic energy in excess of the existing equilibrium generated by the dynamo propagates along the magnetic structure outward, ultimately through the photosphere and into the corona. The medium responds at the local Alfvenic/magnetosonic time scales. In the conventional paradigm, the radially outward electromagnetic energy flux (the Poynting flux) is zero (quasi-static) at the photosphere, while in the new paradigm, the Poynting flux is radially upward. The photosphere is merely a passive opitical (not electromagnetic) boundary, and the implied photospheric motion is of the order of the local Alfven speed. Moreover, the eruption itself is the response to the emerging magnetic flux at the coronal Alfven speed. Thus, eruptions are coronal manifestations of Alfvenic relaxation of coronal magnetic structures in response to the magnetic energy from the dynamo. The distinction of ``slow'' photopheric motion and the ``fast'' coronal motion is merely the difference in the characteristic speeds of the disparate media. We discuss and contrast the different physical systems implied by the two paradigms and possible observational consequences in the photosphere. We conclude that the injection of poloidal flux as a mechanisim for CMEs is more physically compatible with solar eruptions than the traditional paradigm. Chen, J. 1996, JGR, 101, 27499 l Krall, J. et al. 2000, ApJ, 539, 964 Work supported by ONR.

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