AAS 200th meeting, Albuquerque, NM, June 2002
Session 16. Atmospheric Heating and Dynamics I
Oral, Monday, June 3, 2002, 10:00-11:30am, Ballroom C

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[16.08] Why Coronal Flux Tubes Have Axially Invariant Cross-section

P. Bellan (Caltech)

When a steady current flows along a flux tube with a bulging middle, nonlinear, non-conservative forces develop which axially pump fluid from the ends to the middle. Remarkably, this ingestion of fluid into the flux tube causes the flux tube volume to decrease in a manner such that the flux tube develops an axially uniform cross-section as observed in coronal loops. The pumping process produces counter-rotating, counter-streaming bulk motion consistent with observations. Collision between axially counterstreaming fluid elements at a stagnation layer provides bulk heating. A small number of tail particles trapped between approaching axially counterstreaming fluid elements can be Fermi accelerated to very high energies. The dependence of loop bulging on current is calculated using an analytic solution of the Grad-Shafranov relevant to loop geometry and a quantitative criterion is established showing that a rather modest current is required for a loop to attain an axially uniform equilibrium.

Supported by USDOE.

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Bulletin of the American Astronomical Society, 34
© 2002. The American Astronomical Soceity.