Other
Scientific paper
May 2009
adsabs.harvard.edu/cgi-bin/nph-data_query?bibcode=2009spd....40.3705c&link_type=abstract
American Astronomical Society, SPD meeting #40, #37.05; Bulletin of the American Astronomical Society, Vol. 41, p.870
Other
Scientific paper
We present global two-dimensional axisymmetric isothermal MHD simulations of the dynamic evolution of a coronal helmet streamer, driven at the lower boundary by the emergence of a twisted flux rope. By varying both the amount of the toroidal magnetic flux as well as the amount of the detached poloidal flux in the emerged flux rope, we obtain solutions that either settle to a new steady state of a stable helmet streamer containing a flux rope, or result in a loss of equilibrium of the helmet with the underlying flux rope being expelled in a CME-like eruption. We find that the transition from a stable to an eruptive end state does not occur at a single critical value of the total relative magnetic helicity, but depends on the profile of the underlying flux rope. Cases where the detached flux rope contains a higher amount of self helicity, i.e. higher internal twist, are found to become eruptive at a significantly lower total helicity. However, in all of the cases studied, we find that the transition from a stable to eruptive end state takes place at a magnetic energy that is very close to the Aly open field energy. For the eruptive cases, we find that the eruption is not driven by magnetic reconnections behind the flux rope, but is a result of a lack of equilibrium between the upwards directed magnetic pressure and the downwards directed magnetic tension and the gravitational force. For the stable helmets we do not find the formation of significant cavities due to the isothermality and the imposed constant pressure at the lower boundary. However during the eruptions we clearly see the 3-part structure of a CME.
Cottaar Michiel
Fan Ying
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