Abstract Details
| status: | file name: | submitted: | by: |
|---|---|---|---|
| approved | abs.pdf | 2017-03-17 10:56:07 | Linda Sugiyama |
Abstracts
Author: Linda E. Sugiyama
Requested Type: Pre-Selected Invited
Submitted: 2017-03-17 10:53:26
Co-authors: M. Asgari-Targhi
Contact Info:
M.I.T.
Bldg. 26-557, 77 Massachusetts
Cambridge, MA 02139
U.S.A.
Abstract Text:
Coronal loops on the surface of the sun appear to be magnetic flux ropes containing plasma, driven by hidden processes in the solar interior. Unstable loops can lead to large impulsive events such as coronal mass ejections (CMEs) of energetic particles and solar flares that contribute to the earth's space weather and can affect man-made communications, satellites, and electrical power grids. The first consistent steady state loop
model[1], for a section of a nonaxisymmetric toroidal plasma with ends tied in the photosphere, is based on 3D analytic solution of the MHD momentum equation in small inverse aspect ratio, using ideas from toroidal fusion plasmas. The solar gravity, previously neglected, determines the degree of nonaxisymmetry of the density, through a competition between the MHD gravity parameter G=g a/v_A^2 and the plasma beta, where g is the acceleration due to gravity, a the loop minor radius, and v_A the shear Alfven velocity. Gravity pulls the plasma down along the magnetic field lines towards the sun, while temperature buoys it up. Curved current-carrying plasmas are unstable to expansion in major radius. The opposing gravitational force density, at the loop-top, is -nM G h-hat, where nM is the mass density and vector h-hat the solar vertical direction. The maximum gravity scaling G/beta=(a/R)^1 determines the largest steady state loop height. Powers (a/R)^2 and higher correspond to increasingly axisymmetric loops that resemble partial tokamaks. The fixed loop ends allow the local radial force balance to differ from closed fusion plasmas. The solutions fit the observed range of thin coronal loops (a/R= 0.02) that commonly appear in solar active regions. They are also consistent with properties of the fatter, more rarely observed loops (a/R=0.1-0.2) that can generate solar flares and CMEs.
Comments:
Note: the mathematical symbols in the abstract above were altered slightly from the exact pdf version in order to be legible.