Statistics – Computation
Scientific paper
Apr 1994
adsabs.harvard.edu/cgi-bin/nph-data_query?bibcode=1994a%26a...284..985s&link_type=abstract
Astronomy and Astrophysics (ISSN 0004-6361), vol. 284, no. 3, p. 985-999
Statistics
Computation
8
Acoustic Propagation, Chromosphere, Coronal Loops, Magnetohydrodynamics, Shock Waves, Sun, Boundary Conditions, Cartesian Coordinates, Computation, Cylindrical Coordinates, Isothermal Processes, Numerical Analysis, Siphoning, Two Dimensional Models
Scientific paper
We present general two-dimensional solutions for low-beta and subalfvenic stationary MHD flow. Our method of solution applies to any type of boundary conditions. It solves for the perturbation of the magnetic configuration brought about by flows and by the development of shock waves in it. Solutions in cartesian and cylindrical geometries are presented to model flows in coronal loops and counter-Evershed flows above spots. In symmetrical magnetic configurations, when the distribution of pressure at the foot points is symmetrical, the flow is necessarily subsonic. Otherwise it can become supersonic at the summit of the magnetic field line and then passes through a shock. Such shocks cna be very inclined to the magnetic field and the shocked material may form a dense hot sheet around a cooler core, a situation which seems to be observed in cool loops. For asymmetrical magnetic configurations, the flow accelerates towards the low gas pressure foot point and could be subsonic or trans-sonic depending on the pressure difference between the foot points. Loops can have a significant density contrast against their environment only if their energy flux differs markedly from the background one. In asymmetrical loops one leg can be much less dense than the other and poorly visible. Near spots, the sign of the difference of pressure between the two foot points is such as to drive a reverse Evershed flow towards the spot. Additional effects would be needed to drive a direct Evershed flow.
Démoulin Pascal
Heyvaerts Jean
Sauty Christophe
Surlantzis G.
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