Dynamics of plasmoids formed by the current sheet tearing |
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Miroslav Barta Submitted: 2008-09-30 03:01
Context: Moving blob-like features observed in the soft X-ray and EUV range above flare-loops are often interpreted as signatures of plasmoids formed by the current sheet tearing in the flare-associated reconnection process. Aims: We investigate the evolution of the flare-associated current sheet numerically in order to analyse the kinematics and dynamics of plasmoids. The goal is to explain the broad diversity of kinematical properties of the plasmoid signatures recorded by various observational techniques. Methods: We performed a 2-dimensional resistive-MHD numerical simulation of the reconnection starting from the Harris-type current sheet. After identifying the plasmoids, we followed their motion to determine basic kinematical parameters (velocity and acceleration), and we analysed the associated magnetic field topology. Results: The simulation reveals a broad variety of the kinematical/dynamical properties of plasmoids - after formation, a plasmoid can move upward, downward, or can even change its direction of propagation. The highest velocities, in the range of the ambient Alfvén speed, are found in the case of upward propagating plasmoids. The acceleration is determined by the net magnetic field tension of the reconnected field lines. Downwardly propagating plasmoids achieve only a fraction of the ambient Alfvén speed. They strongly decelerate during the coalescence with low-lying flare-loops, when distinct energy-release peaks occur and loop system oscillations are excited. Conclusions: The presented results explain, qualitatively and quantitatively, the broad spectrum of kinematical properties of various observational features attributed to the current-sheet plasmoids.
Authors: Bárta, M.; Vr?nak, B.; Karlický, M.
Projects: None
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Publication Status: A&A 477, Issue 2, January II 2008, pp.649-655
Last Modified: 2008-09-30 09:31
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Interference patterns in solar radio spectra: high-resolution structural analysis of the corona |
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Miroslav Barta Submitted: 2006-01-04 05:47
The relationship between the spectral features of various types of
solar radio bursts and the physical properties of their sources have
been extensively studied by many authors. On the other hand, it is
plausible to accept that the spectral properties of the solar
radio radiation received on the Earth are - besides the physics of the radio
source - influenced by an inter-laying medium that radio waves
propagate through. In particular, the regular structures in the solar
corona - such as coronal
waves, oscillations in shock fronts, the fine structures of coronal loops,
streamer current sheets, etc. - might efficiently filter transferred
radio radiation just as (broad-band) X-rays are filtered by a periodic
atomic structure of crystals; the difference is only in the spatial
scale.
Using the wave optics
methods, we investigate the
prospective influence of
considered coronal structures on the propagating radio
waves originating in an external remote source.
Preliminary results have shown
that the resulting modelled radio emission may recall the spectra of
observed zebra
patterns for the simple 1D density structure considered here and for
a reasonable set of parameters. Conversely, it is
suggested that the
spectra of the zebra patterns might be used for an analysis of those coronal
structures that made these traces on the radiation by methods
similar to those used in crystallography. The possibility of the presence
of such regular small scale
structures in the solar corona is demonstrated. For completeness, a
brief review
of contemporary models of the zebra patterns is provided.
Authors: Barta, M., Karlický, M.
Projects: None
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Publication Status: A&A (accepted)
Last Modified: 2006-01-04 05:47
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