LOOP DENSITY ENHANCEMENT BY NONLINEAR MAGNETOHYDRODYNAMIC WAVES |
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Leon Ofman Submitted: 2003-11-24 08:13
We study the possibility that waves in coronal loops can produce density
enhancements at their tops. The mechanism involved is the ponderomotive force of
standing magnetohydrodynamic (MHD) waves. We study the effect of large amplitude
waves in loops first by using a simple second order one-dimensional MHD model for which
analytical expressions are available, second by solving the time dependent
nonlinear MHD equations in a two-dimensional curved loop model, and finally by
solving the MHD equations in a three-dimensional flux tube configuration. Waves are
launched by an initial transverse velocity profile in the loop with footpoints
fixed in the photosphere. We find that large initial disturbances produce
pressure imbalance along the loop, which results in an upflow from its legs. The
accumulation of mass at the top of the oscillating loop can produce significant
density enhancements for typical coronal conditions. In a later stage, the
pressure gradient becomes dominant and inhibits the concentration of mass at the
loop top. We find that oscillating loops observed by the extreme ultraviolet (EUV)
telescope on board the Transition Region and
Coronal Explorer (TRACE) on 1998 July 14 exhibit emission measure
enhancements consistent with this mechanism.
Authors: J. Terradas, L. Ofman
Projects: TRACE
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Publication Status: submitted to ApJ
Last Modified: 2003-11-24 08:13
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