Nonequilibrium ionization and ambipolar diffusion in solar magnetic flux emergence processes

Nóbrega-Siverio, Daniel; Moreno‐Insertis, F.; Martínez-Sykora, Juan; Carlsson, Mats; Szydlarski, Mikołaj

doi:10.1051/0004-6361/201936944

Cited by 36 publications

(37 citation statements)

References 87 publications

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“…However, self-consistent flux emergence simulations show that the plasma density and temperature in an emerged field can be very different from the background stratification, since the adiabatic expansion of the field naturally forms cooler "bubbles" of magnetised plasma (e.g. Archontis et al 2004;Leake & Linton 2013;Nóbrega-Siverio et al 2020). During our numerical experiment, we have not incorporated such an effect.…”

Section: Discussionmentioning

confidence: 99%

A Cancellation Nanoflare Model for Solar Chromospheric and Coronal Heating. III. 3D Simulations and Atmospheric Response

Syntelis

Priest

2020

ApJ

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Inspired by recent observations suggesting that photospheric magnetic flux cancellation occurs much more frequently than previously thought, we analytically estimated the energy released from reconnection driven by photospheric flux cancellation, and proposed that it can act as a mechanism for chromospheric and coronal heating (Priest et al. 2018). Using two-dimensional simulations we validated the analytical estimates and studied the resulting atmospheric response (Syntelis et al. 2019). In the present work, we set up three-dimensional resistive MHD simulations of two cancelling polarities in a stratified atmosphere with a horizontal external field to further validate and improve upon the analytical estimates. The computational evaluation of the parameters associated with the energy release are in good qualitative agreement with the analytical estimates. The computational Poynting energy flux into the current sheet is in good qualitative agreement with the analytical estimates, after correcting the analytical expression to better account for the horizontal extent of the current sheet. The atmospheric response to the cancellation is the formation of hot ejections, cool ejections, or a combination of both hot and cool ejections, which can appear with a time difference and/or be spatially offset, depending on the properties of the cancelling region and the resulting height of the reconnection. Therefore, during the cancellation, a wide spectrum of ejections can be formed, which can account for the variety of multi-thermal ejections associated with Ellerman bombs, UV bursts and IRIS bombs, and also other ejections associated with small-scale cancelling regions and spicules.

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Section: Discussionmentioning

confidence: 99%

A Cancellation Nanoflare Model for Solar Chromospheric and Coronal Heating. III. 3D Simulations and Atmospheric Response

Syntelis

Priest

2020

ApJ

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“…We note that our simulation does not include the effects of ambipolar diffusion, which has been shown to play an important role in 2.5D flux emergence experiments (e.g., Leake & Arber 2006;Martínez-Sykora et al 2020b;Nóbrega-Siverio et al 2020), and it could affect the visibility of different heating events through changes in temperature and density. However, the 2.5D simulation of Martínez-Sykora et al (2020a) that included the effects of ambipolar diffusion and nonequilibrium ionization of helium also suggests that ALMA Band 3 will observe canopy fibrils that originate from strong concentrations of magnetic field, but it predicts low brightness temperatures (∼4500−5000 K) as consequence of expansion of cool dense plasma to much higher heights than in the 3D case (Loukitcheva et al 2015) constituting a cool canopy.…”

Section: Discussionmentioning

confidence: 99%

ALMA observations of transient heating in a solar active region

Santos

Rodríguez

White

et al. 2020

A&A

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Aims. We aim to investigate the temperature enhancements and formation heights of solar active-region brightenings such as Ellerman bombs (EBs), ultraviolet bursts (UVBs), and flaring active-region fibrils (FAFs) using interferometric observations in the millimeter (mm) continuum provided by the Atacama Large Millimeter/submillimeter Array (ALMA). Methods. We examined 3 mm signatures of heating events identified in Solar Dynamics Observatory observations of an active region and compared the results with synthetic spectra from a 3D radiative magnetohydrodynamic simulation. We estimated the contribution from the corona to the mm brightness using differential emission measure analysis. Results. We report the null detection of EBs in the 3 mm continuum at ∼1.2″ spatial resolution, which is evidence that they are sub-canopy events that do not significantly contribute to heating the upper chromosphere. In contrast, we find the active region to be populated with multiple compact, bright, flickering mm-bursts – reminiscent of UVBs. The high brightness temperatures of up to ∼14 200 K in some events have a contribution (up to ∼7%) from the corona. We also detect FAF-like events in the 3 mm continuum. These events show rapid motions of > 10 kK plasma launched with high plane-of-sky velocities (37 − 340 km s−1) from bright kernels. The mm FAFs are the brightest class of warm canopy fibrils that connect magnetic regions of opposite polarities. The simulation confirms that ALMA should be able to detect the mm counterparts of UVBs and small flares and thus provide a complementary diagnostic for localized heating in the solar chromosphere.

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“…The physical mechanisms resulted by interactions between neutrals and ionized plasmas such as the non-equilibrium ionization, ambipolar diffusion and so on are rarely included in these simulations. Though there are several works about numerical simulations of magnetic flux emergency [140][141][142], MHD waves [60] and local dynamo [143], which have considered the effects of ambipolar diffusion and nonequilibrium ionization. Because of the limited resolution, the artificially assumed magnetic diffusion or numerical diffusion are usually applied to trigger reconnection and heat plasmas.…”

Section: (B) Theories and Numerical Simulationsmentioning

confidence: 99%

Magnetic reconnection in partially ionized plasmas

Murphy

et al. 2020

Proc. R. Soc. A.

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Magnetic reconnection has been intensively studied in fully ionized plasmas. However, plasmas are often partially ionized in astrophysical environments. The interactions between the neutral particles and ionized plasmas might strongly affect the reconnection mechanisms. We review magnetic reconnection in partially ionized plasmas in different environments from theoretical, numerical, observational and experimental points of view. We focus on mechanisms which make magnetic reconnection fast enough to compare with observations, especially on the reconnection events in the low solar atmosphere. The heating mechanisms and the related observational evidence of the reconnection process in the partially ionized low solar atmosphere are also discussed. We describe magnetic reconnection in weakly ionized astrophysical environments, including the interstellar medium and protostellar discs. We present recent achievements about fast reconnection in laboratory experiments for partially ionized plasmas.

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Nonequilibrium ionization and ambipolar diffusion in solar magnetic flux emergence processes

Cited by 36 publications

References 87 publications

A Cancellation Nanoflare Model for Solar Chromospheric and Coronal Heating. III. 3D Simulations and Atmospheric Response

A Cancellation Nanoflare Model for Solar Chromospheric and Coronal Heating. III. 3D Simulations and Atmospheric Response

ALMA observations of transient heating in a solar active region

Magnetic reconnection in partially ionized plasmas

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