Could Switchbacks Originate in the Lower Solar Atmosphere? I. Formation Mechanisms of Switchbacks

Context. We present new insight into the long-standing problem of plasma heating in the lower solar atmosphere in terms of collisional dissipation caused by two-fluid Alfvén waves. Aims. Using numerical simulations, we study Alfvén wave propagation and dissipation in a magnetic flux tube and their heating effect. Methods. We set up 2.5-dimensional numerical simulations with a semi-empirical model of a stratified solar atmosphere and a force-free magnetic field mimicking a magnetic flux tube. We consider a partially ionized plasma consisting of ion + electron and neutral fluids, which are coupled by ion-neutral collisions. Results. We find that Alfvén waves, which are directly generated by a monochromatic driver at the bottom of the photosphere, experience strong damping. Low-amplitude waves do not thermalize sufficient wave energy to heat the solar atmospheric plasma. However, Alfvén waves with amplitudes greater than 0.1 km s−1 drive through ponderomotive force magneto-acoustic waves in higher atmospheric layers. These waves are damped by ion-neutral collisions, and the thermal energy released in this process leads to heating of the upper photosphere and the chromosphere. Conclusions. We infer that, as a result of ion-neutral collisions, the energy carried initially by Alfvén waves is thermalized in the upper photosphere and the chromosphere, and the corresponding heating rate is large enough to compensate radiative and thermal-conduction energy losses therein.

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Mode conversion of two-fluid shocks in a partially-ionised, isothermal, stratified atmosphere

Astronomy and Astrophysics ◽

10.1051/0004-6361/202037848 ◽

2020 ◽

Vol 637 ◽

pp. A97

Author(s):

B. Snow ◽

A. Hillier

Keyword(s):

Solar Atmosphere ◽

Mode Conversion ◽

Frictional Heating ◽

Fast Mode ◽

Compressional Waves ◽

Pressure Scale ◽

Velocity Drift ◽

Two Fluid ◽

Lower Solar Atmosphere

Context. The plasma of the lower solar atmosphere consists of mostly neutral particles, whereas the upper solar atmosphere is mostly made up of ionised particles and electrons. A shock that propagates upwards in the solar atmosphere therefore undergoes a transition where the dominant fluid is either neutral or ionised. An upwards propagating shock also passes a point where the sound and Alfvén speed are equal. At this point the energy of the acoustic shock can separated into fast and slow components. The way the energy is distributed between the two modes depends on the angle of magnetic field. Aims. We aim to investigate the separation of neutral and ionised species in a gravitationally stratified atmosphere. The role of two-fluid effects on the structure of the shocks post-mode-conversion and the frictional heating is quantified for different levels of collisional coupling. Methods. Two-fluid numerical simulations were performed using the (PIP) code of a wave steepening into a shock in an isothermal, partially-ionised atmosphere. The collisional coefficient was varied to investigate the regimes where the plasma and neutral species are weakly, strongly, and finitely coupled. Results. The propagation speeds of the compressional waves hosted by neutral and ionised species vary and, therefore, velocity drift between the two species is produced as the plasma attempts to propagate faster than the neutrals. This is most extreme for a fast-mode shock. We find that the collisional coefficient drastically impacts the features present in the system, specifically the mode conversion height, type of shocks present, and the finite shock widths created by the two-fluid effects. In the finitely-coupled regime, fast-mode shock widths can exceed the pressure scale height, which may lead to a new potential observable of two-fluid effects in the lower solar atmosphere.

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Generation of solar spicules and subsequent atmospheric heating

Science ◽

10.1126/science.aaw2796 ◽

2019 ◽

Vol 366 (6467) ◽

pp. 890-894 ◽

Cited By ~ 24

Author(s):

Tanmoy Samanta ◽

Hui Tian ◽

Vasyl Yurchyshyn ◽

Hardi Peter ◽

Wenda Cao ◽

...

Keyword(s):

Solar Atmosphere ◽

Opposite Polarity ◽

Solar Observatory ◽

Magnetized Plasma ◽

Solar Chromosphere ◽

Solar Dynamics Observatory ◽

Polarity Magnetic Field ◽

Solar Dynamics ◽

Solar Spicules ◽

Lower Solar Atmosphere

Spicules are rapidly evolving fine-scale jets of magnetized plasma in the solar chromosphere. It remains unclear how these prevalent jets originate from the solar surface and what role they play in heating the solar atmosphere. Using the Goode Solar Telescope at the Big Bear Solar Observatory, we observed spicules emerging within minutes of the appearance of opposite-polarity magnetic flux around dominant-polarity magnetic field concentrations. Data from the Solar Dynamics Observatory showed subsequent heating of the adjacent corona. The dynamic interaction of magnetic fields (likely due to magnetic reconnection) in the partially ionized lower solar atmosphere appears to generate these spicules and heat the upper solar atmosphere.

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Collisions, magnetization, and transport coefficients in the lower solar atmosphere

Astronomy and Astrophysics ◽

10.1051/0004-6361/201220738 ◽

2013 ◽

Vol 554 ◽

pp. A22 ◽

Cited By ~ 53

Author(s):

J. Vranjes ◽

P. S. Krstic

Keyword(s):

Solar Atmosphere ◽

Transport Coefficients ◽

Lower Solar Atmosphere

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Magnetic coupling of waves and oscillations in the lower solar atmosphere: can the tail wag the dog?

Philosophical Transactions of The Royal Society A Mathematical Physical and Engineering Sciences ◽

10.1098/rsta.2005.1703 ◽

2005 ◽

Vol 364 (1839) ◽

pp. 351-381 ◽

Cited By ~ 59

Author(s):

Robert Erdélyi

Keyword(s):

Magnetic Fields ◽

Solar Atmosphere ◽

Acoustic Waves ◽

Large Scale ◽

Magnetic Coupling ◽

Small Scale ◽

Coupling Mechanism ◽

Frequency Shifts ◽

Characteristic Features ◽

Lower Solar Atmosphere

Can the ubiquitously magnetic solar atmosphere have any effect on solar global oscillations? Traditionally, solar atmospheric magnetic fields are considered to be somewhat less important for the existence and characteristic features of solar global oscillations ( p , f and the not-yet-observed g -modes). In this paper, I demonstrate the importance of the presence of magnetism and plasma dynamics for global resonant oscillations in the solar atmosphere. In particular, in the lower part of the solar atmosphere there are both coherent and random components of magnetic fields and velocity fields, each of which contribute on its own to the line widths and frequency variations of solar global acoustic waves. Changes in the coherent large-scale atmospheric magnetic fields cause frequency shifts of global oscillations over a solar cycle. The random character of the continuously emerging, more localized, magnetic carpet (i.e. small-scale, possibly even sub-resolution, loops) gives rise to additional frequency shifts. On the other hand, random and organized surface and sub-surface flows, like surface granulation, meridional flows or differential rotation, also affect the coupling mechanism of global oscillations to the lower magnetic atmosphere. The competition between magnetic fields and flows is inevitable. Finally, I shall discuss how solar global oscillations can resonantly interact with the overlaying inhomogeneous lower solar atmosphere embedded in a magnetic carpet. Line width broadening and distorsion of global acoustic modes will be discussed. The latter is suggested to be tested and measured by using ring-analysis techniques.

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