Solar Physics Division Poster Award
Miami, Florida, 2010
"Partial Torus Instability"
by Oscar Olmedo and Jie Zhang
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Abstract
Flux ropes are now generally accepted to be the magnetic configuration of Coronal Mass Ejections (CMEs), which may
be formed prior to during solar eruptions. In this study, we model the flux rope as a current-carrying partial torus
loop with its two footpoints anchored in the photosphere, and investigate its stability in the context of the torus
instability (TI). Previous studies on TI have focused on the configuration oc a cicular torus and revealed the existence
of a critical decay index of the overlying constraining magnetic field. Our study reveals that the critical index in a
function of the fractional number of the partial torus, defined by the ratio between the arc length of the partial torus
above the photosphere and the circumference of a circular torus of equal radius. We refer to this finding the partial
torus instability (PTI). It is found that a partial torus with a smaller fractional number has a smaller critical index,
thus requiring a more graadually decreasing magnetic field to stabilize the flux rope. On the other hand, the partial
torus with a larger fractional number has a larger critical index. In the limit of a circular torus when the fractional
number approaches one, the critical index goes to a maximum value that depends on the distribution of the external
magnetic field. We demonstrate that the partial torus instability helps us to understand the confinement, growth, and
eventual eruption of a flux rope CME.
Olmedo (right) and Dr. Zhang (left) standing in front of the poster at the 2010 SPD meeting