Astronomy and Astrophysics – Astrophysics
Scientific paper
May 1997
adsabs.harvard.edu/cgi-bin/nph-data_query?bibcode=1997phdt.........6g&link_type=abstract
Thesis (PHD). STANFORD UNIVERSITY , Source DAI-B 57/11, p. 6985, May 1997, 100 pages.
Astronomy and Astrophysics
Astrophysics
1
Magnetic Field, Photosphere, Larmor Radius
Scientific paper
Equilibrium states and stability of partially open magentic field structures in the solar corona are studied. Soft X-ray observations of the birth and evolution of a giant coronal helmet streamer suggest that the energy source responsible for the X-ray manifestation of the structure is most probably located in the lower corona. The downward heat flux is the indication that a significant part of the source's energy is transported to the top of the structure and converted there to a disposable form. It is shown that by applying the thermodynamic equilibrium model of the corona to the two-dimensional X-ray data it is possible to reconstruct the three-dimensional form of the coronal helmet. The general significance of the projective geometry effects for the observation of the solar corona is discussed. The hypothesis of thermal pressure increase as the cause of the observed helmet expansion is verified numerically. It is shown that in the solar corona a relatively small variations of the pressure distribution in the closed field region can cause huge variations in the geometry of a coronal helmet streamer. Numerical simulations of the morphology and energy accumulation in helmet-like structures subject to photospheric shear motion show that the magnetic field surrounding a partially open structure can inhibit catastrophic expansion of the structure as its energy grows. Stability of a coronal streamer in the framework of the neutral current sheet model is studied theoretically. It is shown that effects of viscosity and the finite Larmor radius dominate effects of inertial fluid motion in the tearing mode instability of a neutral current sheet. Two new regimes of the instability are discovered. It is proven that in the solar corona the rates of growth of the neutral current sheet instability are much smaller than previously believed. Implications of the obtained results are discussed.
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