Solar prominences: 'double, double . . . boil and bubble' |
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Chun Xia Submitted: 2015-05-21 01:49
Observations revealed rich dynamics within prominences, the cool (10,000 K), macroscopic (sizes of order 100 Mm) 'clouds' in the million degree solar corona. Even quiescent prominences are continuously perturbed by hot, rising bubbles. Since prominence matter is hundredfold denser than coronal plasma, this bubbling is related to Rayleigh-Taylor instabilities. Here we report on true macroscopic simulations well into this bubbling phase, adopting a magnetohydrodynamic description from chromospheric layers up to 30 Mm height. Our virtual prominences rapidly establish fully non-linear (magneto)convective motions where hot bubbles interplay with falling pillars, with dynamical details including upwelling pillars forming within bubbles. Our simulations show impacting Rayleigh-Taylor fingers reflecting on transition region plasma, ensuring that cool, dense chromospheric material gets mixed with prominence matter up to very large heights. This offers an explanation for the return mass cycle mystery for prominence material. Synthetic views at extreme ultraviolet wavelengths show remarkable agreement with observations, with clear indications of shear-flow induced fragmentations.
Authors: Rony Keppens and Chun Xia
Projects: None
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Publication Status: ApJ Letter accepted
Last Modified: 2015-05-25 09:30
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Simulating the in situ condensation process of solar prominences |
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Chun Xia Submitted: 2014-08-21 14:38
Prominences in the solar corona are hundredfold cooler and denser than their surroundings, with a total mass of 1.e13 up to 1.e15 g. Here we report on the first comprehensive simulations of three-dimensional, thermally and gravitationally stratified magnetic flux ropes, where in situ condensation to a prominence happens due to radiative losses. After a gradual thermodynamic adjustment, we witness a phase where runaway cooling happens while counter-streaming shearing flows drain off mass along helical field lines. After this drainage, a prominence-like condensation resides in concave upward field regions, and this prominence retains its overall characteristics for more than two hours. While condensing, the prominence establishes a prominence-corona transition region, where magnetic field-aligned thermal conduction is operative during the runaway cooling. The prominence structure represents a force-balanced state in a helical flux rope. The simulated condensation demonstrates a right-bearing barb, as a remnant of the drainage. Synthetic images at extreme ultraviolet wavelengths follow the onset of the condensation, and confirm the appearance of horns and a three-part structure for the stable prominence state, as often seen in erupting prominences. This naturally explains recent Solar Dynamics Observatory views with the Atmospheric Imaging Assembly on prominences in coronal cavities demonstrating horns.
Authors: Chun Xia, Rony Keppens, Patrick Antolin, Oliver Porth
Projects: None
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Publication Status: accepted in ApJ Letter
Last Modified: 2014-08-27 12:58
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Simulations of Prominence Formation in the Magnetized Solar Corona by Chromospheric Heating |
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Chun Xia Submitted: 2012-02-28 19:13
Starting from a realistically sheared magnetic arcade connectingchromospheric, transition region to coronal plasma, we simulate thein-situformation and sustained growth of a quiescent prominence in the solarcorona.Contrary to previous works, our model captures all phases of theprominenceformation, including the loss of thermal equilibrium, its successivegrowth inheight and width to macroscopic dimensions, and the gradual bending ofthearched loops into dipped loops, as a result of the mass accumulation.Our2.5-dimensional, fully thermodynamically and magnetohydrodynamicallyconsistentmodel mimics the magnetic topology of normal-polarity prominencesabove aphotospheric neutral line, and results in a curtain-like prominenceabove theneutral line through which the ultimately dipped magnetic field linesprotrudeat a finite angle. The formation results from concentrated heating inthechromosphere, followed by plasma evaporation and later rapidcondensation inthe corona due to thermal instability, as verified by linear instabilitycriteria. Concentrated heating in the lower atmosphere evaporatesplasma frombelow to accumulate at the top of coronal loops and supply mass to thelaterprominence constantly. This is the first evaporation-condensationmodel studywhere we can demonstrate how the formed prominence stays in a forcebalancedstate, which can be compared to the Kippenhahn-Schluter typemagnetohydrostaticmodel, all in a finite low-beta corona.
Authors: Chun Xia, P. F. Chen, and Rony Keppens
Projects: None
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Publication Status: ApJ Letter (accepted)
Last Modified: 2012-02-29 08:25
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Formation of Solar Filaments by Steady and Nonsteady Chromospheric Heating |
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Chun Xia Submitted: 2011-05-31 23:38
It has been established that cold plasma condensations can form in a magneticloop subject to localized heating of the footpoints. In this paper, we usegrid-adaptive numerical simulations of the radiative hydrodynamic equations toparametrically investigate the filament formation process in a pre-shaped loopwith both steady and finite-time chromospheric heating. Compared to previousworks, we consider low-lying loops with shallow dips, and use a more realisticdescription for the radiative losses. We demonstrate for the first time thatthe onset of thermal instability satisfies the linear instability criterion.The onset time of the condensation is roughly sim 2 hr or more after thelocalized heating at the footpoint is effective, and the growth rate of thethread length varies from 800 km hr-1 to 4000 km hr-1, depending on theamplitude and the decay length scale characterizing this localizedchromospheric heating. We show how single or multiple condensation segments mayform in the coronal portion. In the asymmetric heating case, when two segmentsform, they approach and coalesce, and the coalesced condensation later drainsdown into the chromosphere. With a steady heating, this process repeats with aperiodicity of several hours. While our parametric survey confirms and augmentsearlier findings, we also point out that steady heating is not necessary tosustain the condensation. Once the condensation is formed, it can keep growingalso when the localized heating ceases. Finally, we show that the condensationcan survive continuous buffeting by perturbations resulting from thephotospheric p-mode waves.
Authors: C. Xia, P. F. Chen, R. Keppens, A. J. van Marle
Projects:
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Publication Status: ApJ(accepted)
Last Modified: 2011-06-01 21:19
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