MHD mode conversion in a stratified atmosphere

McDougall, Alistair; Hood, A. W.

doi:10.1017/s1743921308014993

Cited by 4 publications

(3 citation statements)

References 5 publications

Supporting

Mentioning

Contrasting

Order By: Relevance

“…Linear mode conversion on the other hand is more universal for magnetosonic waves [see e.g. Zhugzhda (1979); Zhugzhda & Dzhalilov (1981, 1982a; Cally (2001); McDougall & Hood (2007a,b, 2009 for similar linear mode conversion for magnetogravity waves at the magnetic canopy in solar chromosphere]. Finally, resonance can happen for Alfvén mode, where the well-known Alfvén resonance can generate secondary Slow and Fast waves [see Hollweg (1971) or Appendix-A, and simulation in Figure 3].…”

Section: Discussionmentioning

confidence: 99%

Conservation of Total Wave Action in the Expanding Solar Wind

Huang,

Shi,

Velli

et al. 2022

Preprint

View full text Add to dashboard Cite

The conservation of wave action in moving plasmas has been well-known for over half a century. However, wave action is not conserved when multiple wave modes propagate and coexist close to degeneration condition (Sound speed equals Alfvén speed, i.e. plasma β ∼ 1). Here we show that the violation of conservation is due to wave mode conversion, and that the total wave action summed over interacting modes is still conserved. Though the result is general, we focus on MHD waves and identify three distinctive mode conversion mechanisms, i.e. degeneracy, linear mode conversion, and resonance, and provide an intuitive physical picture for the mode conversion processes. We use 1D MHD simulations with the Expanding Box Model to simulate the nonlinear evolution of monochromatic MHD waves in the expanding solar wind. Simulation results validate the theory; total wave action therefore remains an interesting diagnostic for studies of waves and turbulence in the solar wind.

show abstract

Section: Discussionmentioning

confidence: 99%

Conservation of Total Wave Action in the Expanding Solar Wind

Huang,

Shi,

Velli

et al. 2022

Preprint

View full text Add to dashboard Cite

show abstract

“…In future we plan to extend the Cairns and Lashmore-Davies [3] method to two dimensions, allowing the quantity of conversion and transmission to be calculated, as has been done for an isothermal [2], and non-isothermal [4], one-dimensional model.…”

Section: Discussionmentioning

confidence: 99%

“…This method has the advantage that an exact analytical solution need not be known. This was extended to include a non-isothermal atmosphere [4], where it was found that the same conversion and transmission coefficients apply. Mode conversion around a two-dimensional, magnetic null point has also been investigated [5].…”

Section: Introductionmentioning

confidence: 99%

MHD Mode Conversion around a 2D Magnetic Null Point

McDougall¹,

Hood²

2009

AIP Conference Proceedings

View full text Add to dashboard Cite

Abstract.Mode conversion occurs when a wave passes through a region where the sound and Alfvén speeds are equal. At this point there is a resonance, which allows some of the incident wave to be converted into a different mode. We study this phenomenon in the vicinity of a twodimensional, coronal null point. As a wave approaches the null it passes from low-to high-β plasma, allowing conversion to take place. We simulate this numerically by sending in a slow magnetoacoustic wave from the upper boundary; as this passes through the conversion layer a fast wave can clearly be seen propagating ahead. Numerical simulations combined with an analytical WKB investigation allow us to determine and track both the incident and converted waves throughout the domain.

show abstract

Oscillatory Response of the 3D Solar Atmosphere to the Leakage of Photospheric Motion

2009

View full text Add to dashboard Cite

The direct propagation of acoustic waves, driven harmonically at the solar photosphere, into the three-dimensional solar atmosphere is examined numerically in the framework of ideal magnetohydrodynamics. It is of particular interest to study the leakage of 5-minute global solar acoustic oscillations into the upper, gravitationally stratified and magnetised atmosphere, where the modelled solar atmosphere possesses realistic temperature and density stratification. This work aims to complement and bring further into the 3D domain our previous efforts (by Erdélyi et al., 2007, Astron. Astrophys. 467, 1299 on the leakage of photospheric motions and running magnetic-field-aligned waves excited by these global oscillations. The constructed model atmosphere, most suitable perhaps for quiet Sun regions, is a VAL IIIC derivative in which a uniform magnetic field is embedded. The response of the atmosphere to a range of periodic velocity drivers is numerically investigated in the hydrodynamic and magnetohydrodynamic approximations. Among others the following results are discussed in detail: i) High-frequency waves are shown to propagate from the lower atmosphere across the transition region, experiencing relatively low reflection, and transmitting most of their energy into the corona; ii) the thin transition region becomes a wave guide for horizontally propagating surface waves for a wide range of driver periods, and particularly at those periods that support chromospheric standing waves; iii) the magnetic field acts as a waveguide for both high-and low-frequency waves originating from the photosphere and propagating through the transition region into the solar corona. Electronic supplementary materialThe online version of this article (http://dx.doi.org/10.1007/s11207-009-9407-9) contains supplementary material, which is available to authorized users.V. Fedun ( ) · R. Erdélyi · S. Shelyag

show abstract

MHD mode conversion in a stratified atmosphere

Cited by 4 publications

References 5 publications

Conservation of Total Wave Action in the Expanding Solar Wind

Conservation of Total Wave Action in the Expanding Solar Wind

MHD Mode Conversion around a 2D Magnetic Null Point

Oscillatory Response of the 3D Solar Atmosphere to the Leakage of Photospheric Motion

Contact Info

Product

Resources

About