Astronomy and Astrophysics – Astrophysics
Scientific paper
Nov 1992
adsabs.harvard.edu/cgi-bin/nph-data_query?bibcode=1992stan.reptq....s&link_type=abstract
Annual Technical Report, 1 Oct. 1991 - 1 Oct. 1992 Stanford Univ., CA. Center for Space Science and Astrophysics.
Astronomy and Astrophysics
Astrophysics
Chromosphere, Magnetic Field Configurations, Magnetohydrodynamic Stability, Magnetohydrodynamic Waves, Photosphere, Solar Activity, Solar Corona, Solar Flares, Solar Magnetic Field, Solar X-Rays, Stellar Mass Ejection, Boundary Conditions, Convection, Geopotential Height, Nonlinear Systems, Solar Heating, Turbulence
Scientific paper
This report describes progress toward understanding the theoretical basis for solar activity. One of our key accomplishments has been the insight we have gained into the eruption of coronal magnetic structures. Roumeliotis, Sturrock, and Antiochos have made numerical and analytic calculations which indicate that coronal magnetic fields being sheared by convective motions acting on their photospheric footpoints evolve smoothly until the shear surpasses a certain critical amount. After that, the coronal field exhibits very sensitive dependence on the photospheric boundary conditions, in the sense that small changes in the footpoint displacements produce huge changes in the height of the coronal field. We propose that this nonlinear behavior of sheared magnetic fields is the explanation for eruptive phenomena such as coronal mass ejections and solar flares. We are also developing several approaches for understanding coronal heating. In particular, Sturrock has proposed a model in which turbulent reconnection deep within the chromosphere produces local heating as well as a burst of magnetohydrodynamic waves that propagate upward to heat the corona. Roumeliotis is working on the theory that twisted flux loops in the corona undergo an internal resistive kink instability that unwinds the internal field and releases magnetic energy to heat the loop.
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