34th Solar Physics Division Meeting, June 2003
Session 4 Corona II
Poster, Monday, June 16, 2003, 3:30-5:00pm, Mezzanine

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[4.02] Coronal Loops as Van der Pol Oscillators: Theory and Observations

M. P. Ryutova (LLNL/IGPP)

We study formation and dynamics of coronal loops associated with various magnetic fields in the underlying photosphere, from an isolated sunspot penumbra to plage regions with newly emerged magnetic fluxes. We use coordinated observations from Swedish Vacuum Solar Telescope (SVST) on La Palma, the TRACE satellite and the MDI instrument on SOHO. High resolution MDI magnetograms are assembled in a 6-hour movie and co-aligned with TRACE Fe IX/X 171 Å images of the corona, H-alpha filtergrams showing plasma motions at the chromospheric level. This allowed us to follow the process of loop formation from its very early stage and establish links between different stages of the process and corresponding changes in underlying atmosphere. We found that the dynamics of coronal loops, e.g. whether the loops exhibit a ``steady'', oscillatory or flaring behavior, strongly depends on the underlying photospheric magnetic pattern. We propose a mechanism to explain magneto-hydrodynamic coupling between the photospheric magnetic fields and various types of coronal structures based on the time-dependent electric circuit analogue. In nonlinear regime the LRC equation acquires the form of Van der Pol oscillator with dissipation and external driving force. Plasma conditions in the overlying chromosphere and corona determine the main components of the circuit. Depending on these components and the character of the energy source (e.g. electro-mechanical driver in the photosphere) the formed circuit may exhibit various regimes including the meta-stable oscillatory behavior, explosive disruption and others. This work is supported by NASA through the MDI project at Stanford & Lockheed Martin (NAG510483).

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Bulletin of the American Astronomical Society, 35 #3
© 2003. The American Astronomical Soceity.