Structure and Flows in Coronal Loops
- C. T. Russell,
- E. R. Priest and
- L. C. Lee
Published Online: 21 MAR 2013
Copyright 1990 by the American Geophysical Union.
Physics of Magnetic Flux Ropes
How to Cite
Antiochos, S. K. (1990) Structure and Flows in Coronal Loops, in Physics of Magnetic Flux Ropes (eds C. T. Russell, E. R. Priest and L. C. Lee), American Geophysical Union, Washington, D. C.. doi: 10.1029/GM058p0203
- Published Online: 21 MAR 2013
- Published Print: 1 JAN 1990
Print ISBN: 9780875900261
Online ISBN: 9781118663868
- Solar photosphere;
- Magnetic flux;
The canonical model for the structure of the solar coronal plasma is a collection of loops. Each loop is believed to correspond to a magnetic flux tube in which the field dominates the plasma. In this review we discuss plasma flows in solar loops. The field is approximated as completely rigid since the plasma beta in the corona is very low, and the observed time scales of the motions are typically much longer than the Alfven time scales.
First, a brief overview of observations is presented; in particular the redshifts observed in UV emission lines. Next we review the work on steady-state flows in coronal loops. An important point is that static models, although widely used, are not totally valid since any asymmetry in the loop geometry, in the coronal heating, or in the chromospheric boundary conditions will result in a “siphon” flow along the loop. We discuss whether such flows can account for the observed redshifts, and conclude that the siphon flow models require extreme and contrived assumptions on the heating process in order to fit the data. We also discuss the possible importance of non-equilibrium ionization in these models, and conclude that the velocities deduced from the observed line shifts imply ionization non-equilibrium in the lower transition region, T < 105 K. Finally, we review work on flows due to impulsive heating in coronal loops. We argue that implusive heating may be able to account for the observed redshifts, but conclude that much more work is needed in order to verify or disprove this conjecture.