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Correlated dynamics of hot and cool plasmas in the main phase of a solar flare  

Bernhard Kliem   Submitted: 2002-03-04 11:58

We report far-ultraviolet observations of a solar limb flare obtained by the Solar Ultraviolet Measurements of Emitted Radiation (SUMER) spectrometer. At a fixed pointing of the slit above the limb, spectra were simultaneously obtained in several emission lines that covered a wide temperature range from approx!104 to approx!107 K. The temporal evolution of the spectra revealed, for the first time, a high degree of correlation between the dynamical behavior of hot (Tsim107 K) and cool (Tsim104 K) coronal material during the main phase of a flare. We note that the data did not show any indication of the presence of a prominence. Hot and cool plasmas brightened at nearly the same location. Their Doppler shifts, which were opposite to each other, reached peak values simultaneously. Thereafter, the two components showed anti-correlated, rapidly damped, and oscillatory Doppler shifts and a very similar decay of the line widths, but with the cool plasma reaching maximum brightness before the hot plasma. This behavior points to an active role for cool plasma in the dynamics of this flare, different from the usual picture of passive cooling after the impulsive phase. We suggest a model in which the localized cooling of coronal plasma by the thermal instability triggers magnetic reconnection through the resulting enhanced resistivity, the combined processes leading to the correlated dynamics of hot and cool plasmas in a loop-loop interaction geometry.

Authors: B. Kliem, I. E. Dammasch, W. Curdt, and K. Wilhelm
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Publication Status: ApJ Lett (in press)
Last Modified: 2002-03-04 11:58
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Solar flare radio pulsations as a signature of dynamic magnetic reconnection  

Bernhard Kliem   Submitted: 2000-06-22 21:04

Decimetric radio observations of the impulsive solar flare on October 5, 1992, 09: 25 UT show a long series of quasi-periodic pulsations deeply modulating a continuum in the 0.6-2 GHz range that is slowly drifting toward lower frequencies. We propose a model in which the pulsations of the radio flux are caused by quasi-periodic particle acceleration episodes that result from a dynamic phase of magnetic reconnection in a large-scale current sheet. The reconnection is dominated by repeated formation and subsequent coalescence of magnetic islands (known as ``secondary tearing'' or ``impulsive bursty'' regime of reconnection), while a continuously growing plasmoid is fed by newly coalescing islands. Such a model, involving a current sheet and a growing plasmoid, is consistent with the Yohkoh observations of the same flare (Ohyama & Shibata 1998). We present two-dimensional MHD simulations of dynamic magnetic reconnection that support the model. Within the framework of the proposed interpretation, the radio observations reveal details of plasmoid formation in flares.

Authors: Kliem, B., Karlický, M., Benz, A. O.
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Publication Status: A&A (in press)
Last Modified: 2000-06-22 21:04
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Three-dimensional spontaneous magnetic reconnection in neutral current sheets  

Bernhard Kliem   Submitted: 2000-06-22 21:04

Magnetic reconnection in an antiparallel uniform Harris current sheet equilibri- equilibrium, which is initially perturbed by a region of enhanced resistivity limited in all three dimensions, is investigated through compressible magnetohy- magnetohydrodynamic simulations. Variable resistivity, coupled to the dynamics of the plasma by an electron-ion drift velocity criterion, is used during the evolution. A phase of magnetic reconnection amplifying with time and leading to eruptive energy release is triggered only if the initial perturbation is strongly elongated in the direction of current flow or if the threshold for onset of anomalous resistivity is significantly lower than in the corresponding two-dimensional case. A Petschek-like configuration is then built up for sim102 Alfvén times, but remains localized in the third dimension. Subsequently, a change of topology to an O-line at the center of the system (``secondary tearing'') occurs. This leads to enhanced and time-variable reconnection, to a second pair of outflow jets directed along the O-line, and to expansion of the reconnection process into the third dimension. High parallel current density components are created mainly near the region of enhanced resistivity.

Authors: Schumacher, J., Kliem, B., Seehafer, N.
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Publication Status: Phys. Plasmas 7, 108 (2000)
Last Modified: 2000-06-22 21:04
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MSU Solar Physics.
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Max Millennium Flare Catalog

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