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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

Publication Status: submitted to ApJ
Last Modified: 2003-11-24 08:13
Go to main E-Print page  Evidence of Rapid Flux Emergence Associated with the M8.7 Flare on 2003 July 26  Helicity of magnetic clouds and their associated active regions  Edit Entry  Download Preprint  Delete Entry 

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