scholarly journals High frequency generation in the corona: Resonant cavities

2018 ◽  
Vol 611 ◽  
pp. A10 ◽  
Author(s):  
I. C. Santamaria ◽  
T. Van Doorsselaere
Keyword(s):  
Magnetic Field ◽  
Shock Wave ◽  
Acoustic Waves ◽  
High Frequency ◽  
Spatial Scales ◽  
Wave Train ◽  
Null Point ◽  
Solar Chromosphere ◽  
High Frequency Region ◽  
Frequency Wave

Aims. Null points are prominent magnetic field singularities in which the magnetic field strength strongly decreases in very small spatial scales. Around null points, predicted to be ubiquitous in the solar chromosphere and corona, the wave behavior changes considerably. Null points are also responsible for driving very energetic phenomena, and for contributing to chromospheric and coronal heating. In previous works we demonstrated that slow magneto-acoustic shock waves were generated in the chromosphere propagate through the null point, thereby producing a train of secondary shocks escaping along the field lines. A particular combination of the shock wave speeds generates waves at a frequency of 80 MHz. The present work aims to investigate this high frequency region around a coronal null point to give a plausible explanation to its generation at that particular frequency. Methods. We carried out a set of two-dimensional numerical simulations of wave propagation in the neighborhood of a null point located in the corona. We varied both the amplitude of the driver and the atmospheric properties to investigate the sensitivity of the high frequency waves to these parameters. Results. We demonstrate that the wave frequency is sensitive to the atmospheric parameters in the corona, but it is independent of the strength of the driver. Thus, the null point behaves as a resonant cavity generating waves at specific frequencies that depend on the background equilibrium model. Moreover, we conclude that the high frequency wave train generated at the null point is not necessarily a result of the interaction between the null point and a shock wave. This wave train can be also developed by the interaction between the null point and fast acoustic-like magneto-acoustic waves, that is, this interaction within the linear regime.

High-frequency acoustic waves are not sufficient to heat the solar chromosphere

Nature ◽  
2005 ◽  
Vol 435 (7044) ◽  
pp. 919-921 ◽  
Author(s):  
Astrid Fossum ◽  
Mats Carlsson
Keyword(s):  
Acoustic Waves ◽  
High Frequency ◽  
Solar Chromosphere

New model for acoustic waves propagating through a vortical flow

2017 ◽  
Vol 823 ◽  
pp. 658-674 ◽  
Author(s):  
Jim Thomas
Keyword(s):  
Asymptotic Analysis ◽  
Wave Field ◽  
Time Scale ◽  
Acoustic Waves ◽  
High Frequency ◽  
Spatial Scales ◽  
Amplitude Equation ◽  
Vortical Flow ◽  
Reduced Model ◽  
Scale Separation

A new amplitude equation is derived for high-frequency acoustic waves propagating through an incompressible vortical flow using multi-time-scale asymptotic analysis. The reduced model is derived without an explicit spatial-scale separation ansatz between the wave and vortical fields. As a consequence, the model is seen to capture very well the features of the wave field in the regime where the spatial scales of the wave and vortical fields are comparable, a regime for which an optimal reduced model does not seem to be available.

scholarly journals Photospheric high-frequency acoustic power excess in sunspot umbra: signature of magneto-acoustic modes

2013 ◽  
Vol 31 (8) ◽  
pp. 1357-1364 ◽  
Author(s):  
S. Zharkov ◽  
S. Shelyag ◽  
V. Fedun ◽  
R. Erdélyi ◽  
M. J. Thompson
Keyword(s):  
Magnetic Field ◽  
Acoustic Waves ◽  
High Frequency ◽  
Acoustic Power ◽  
Solar Photosphere ◽  
Heliospheric Observatory ◽  
Magnetohydrodynamic Waves ◽  
Sunspot Umbra ◽  
Doppler Imager ◽  
Power Enhancement

Abstract. We present observational evidence for the presence of MHD (magnetohydrodynamic) waves in the solar photosphere deduced from SOHO/MDI (Solar and Heliospheric Observatory/Michelson Doppler Imager) Dopplergram velocity observations. The magneto-acoustic perturbations are observed as acoustic power enhancement in the sunspot umbra at high-frequency bands in the velocity component perpendicular to the magnetic field. We use numerical modelling of wave propagation through localised non-uniform magnetic field concentration along with the same filtering procedure as applied to the observations to identify the observed waves. Guided by the results of the numerical simulations we classify the observed oscillations as magneto-acoustic waves excited by the trapped sub-photospheric acoustic waves. We consider the potential application of the presented method as a diagnostic tool for magnetohelioseismology.

Numerical modelling of MHD waves in the solar chromosphere

2005 ◽  
Vol 364 (1839) ◽  
pp. 395-404 ◽  
Author(s):  
Mats Carlsson ◽  
Thomas J Bogdan
Keyword(s):  
Magnetic Field ◽  
Acoustic Waves ◽  
Mode Conversion ◽  
Three Dimensions ◽  
Mhd Waves ◽  
Solar Chromosphere ◽  
Fast Mode ◽  
Reflected Waves ◽  
The Waves ◽  
The Magnetic Field

Acoustic waves are generated by the convective motions in the solar convection zone. When propagating upwards into the chromosphere they reach the height where the sound speed equals the Alfvén speed and they undergo mode conversion, refraction and reflection. We use numerical simulations to study these processes in realistic configurations where the wavelength of the waves is similar to the length scales of the magnetic field. Even though this regime is outside the validity of previous analytic studies or studies using ray-tracing theory, we show that some of their basic results remain valid: the critical quantity for mode conversion is the angle between the magnetic field and the k-vector: the attack angle. At angles smaller than 30° much of the acoustic, fast mode from the photosphere is transmitted as an acoustic, slow mode propagating along the field lines. At larger angles, most of the energy is refracted/reflected and returns as a fast mode creating an interference pattern between the upward and downward propagating waves. In three-dimensions, this interference between waves at small angles creates patterns with large horizontal phase speeds, especially close to magnetic field concentrations. When damping from shock dissipation and radiation is taken into account, the waves in the low–mid chromosphere have mostly the character of upward propagating acoustic waves and it is only close to the reflecting layer we get similar amplitudes for the upward propagating and refracted/reflected waves. The oscillatory power is suppressed in magnetic field concentrations and enhanced in ring-formed patterns around them. The complex interference patterns caused by mode-conversion, refraction and reflection, even with simple incident waves and in simple magnetic field geometries, make direct inversion of observables exceedingly difficult. In a dynamic chromosphere it is doubtful if the determination of mean quantities is even meaningful.

scholarly journals Acoustic oscillations in a field-free cavity under solar small-scale bipolar magnetic canopy

2008 ◽  
Vol 26 (10) ◽  
pp. 2983-2989 ◽  
Author(s):  
D. Kuridze ◽  
T. V. Zaqarashvili ◽  
B. M. Shergelashvili ◽  
S. Poedts
Keyword(s):  
Magnetic Field ◽  
Acoustic Waves ◽  
Canopy Structure ◽  
Active Regions ◽  
Acoustic Power ◽  
Lower Atmosphere ◽  
Wave Number ◽  
Small Scale ◽  
Acoustic Oscillations ◽  
Frequency Wave

Abstract. Observations show the increase of high-frequency wave power near magnetic network cores and active regions in the solar lower atmosphere. This phenomenon can be explained by the interaction of acoustic waves with a magnetic field. We consider small-scale, bipolar, magnetic field canopy structure near the network cores and active regions overlying field-free cylindrical cavities of the photosphere. Solving the plasma equations we get the analytical dispersion relation of acoustic oscillations in the field-free cavity area. We found that the m=1 mode, where m is azimuthal wave number, cannot be trapped under the canopy due to energy leakage upwards. However, higher (m≥2) harmonics can be easily trapped leading to the observed acoustic power halos under the canopy.

scholarly journals High frequency oscillations in the solar chromosphere and their connection with heating

2007 ◽  
Vol 3 (S247) ◽  
pp. 312-315 ◽  
Author(s):  
Aleksandra Andic ◽  
M. Mathioudakis ◽  
F. P. Keenan ◽  
D. B. Jess ◽  
D. S. Bloomfield
Keyword(s):  
Magnetic Fields ◽  
Acoustic Waves ◽  
High Frequency ◽  
Solar Observatory ◽  
Solar Chromosphere ◽  
Frequency Interval ◽  
Solar Telescope ◽  
National Solar Observatory ◽  
High Frequency Oscillations ◽  
Using Data

AbstractHigh frequency acoustic waves have been suggested as a source of mechanical heating in the quiet solar chromosphere. To investigate this, we have observed intensity oscillations of several lines in the frequency interval 1.64-70mHz using data from the VTT Tenerife and the Dunn Solar Telescope at the National Solar Observatory. Our analysis of Fe i 543.45 nm, Fe i 543.29 nm and the G-band, indicate that the majority of oscillations are connected with the magnetic fields and do not provide sufficient mechanical flux for the heating of the chromosphere. This correlation is also observed in quiet Sun areas.

scholarly journals High-frequency Wave Power Observed in the Solar Chromosphere with IBIS and ALMA

2021 ◽  
Vol 920 (2) ◽  
pp. 125
Author(s):  
Momchil E. Molnar ◽  
Kevin P. Reardon ◽  
Steven R. Cranmer ◽  
Adam F. Kowalski ◽  
Yi Chai ◽  
...  
Keyword(s):  
High Frequency ◽  
Wave Power ◽  
Solar Chromosphere ◽  
Frequency Wave ◽  
High Frequency Wave

High-frequency magnetic field on crystal field diluted S = 1 Ising system: magnetic relaxation near continuous phase transition points

2018 ◽  
Vol 96 (12) ◽  
pp. 1321-1332 ◽  
Author(s):  
Gül Gülpınar ◽  
Rıza Erdem
Keyword(s):  
Magnetic Field ◽  
Crystal Field ◽  
High Frequency ◽  
Low Frequency ◽  
Continuous Phase ◽  
Irreversible Thermodynamics ◽  
Critical Temperatures ◽  
High Frequency Region ◽  
Magnetization Relaxation ◽  
Transition Points

Magnetization relaxation and the steady state response of the S = 1 Ising model with random crystal field to a time varying magnetic field with a frequency ω is modelled and studied here by a method that combines the statistical equilibrium theory with the theory of irreversible thermodynamics. The method offers information on the relaxation time (τ) of the system as well as the temperature (θ) and ω dependencies of the complex (AC or dynamical) susceptibility (i.e., χ(ω) = χ′(ω) − iχ″(ω)). The so-called low- and high-frequency regions are separated by τ because τ−1 → 0 as θ approaches the critical temperatures (θc). One can choose to keep the frequency ω fixed and observe the low-frequency behaviors followed by the high-frequency behaviors when θ → θc. It is shown that χ(ω) exhibits different behaviors in low- and high-frequency regimes that are separated by the quantity ωτ: χ′(ω) converges to static susceptibility and χ″(ω) → 0 for ωτ ≪ 1. However, in the high-frequency region where ωτ ≫ 1, χ′(ω) vanishes and χ″(ω) displays a peak at the critical temperature (θc). Besides the above, the logarithm of the susceptibility components versus log(ω) is also plotted. From these plots, one plateau (a step-like) region and a shifted peak with rising temperature is observed for the real and imaginary parts, respectively.

scholarly journals The Heating of the Quiet Solar Chromosphere

1990 ◽  
Vol 142 ◽  
pp. 197-206
Author(s):  
Wolfgang Kalkofen
Keyword(s):  
Magnetic Field ◽  
Field Strength ◽  
Acoustic Waves ◽  
Solar Chromosphere ◽  
Temperature Structure ◽  
Cell Interior ◽  
Long Period ◽  
Low Field ◽  
Magnetic Elements ◽  
Short Period

The quiet solar chromosphere shows three distinct regions. Ordered according to the strength of the emission from the low and middle chromosphere they are (1) the magnetic elements on the boundary of supergranulation cells, (2) the bright points in the cell interior, and (3) the truly quiet chromosphere, also in the cell interior. The magnetic elements on the cell boundary are associated with intense magnetic fields and are heated by waves with very long periods, ranging from six to twelve minutes; the bright points are associated with magnetic elements of low field strength and are heated by (long-period) waves with periods near the acoustic cutoff period of three minutes; and the quiet cell interior, which is free of magnetic field, may be heated by short-period acoustic waves, with periods below one minute. This paper reviews mainly the heating of the bright points and concludes that the large-amplitude, long-period waves heating the bright points dissipate enough energy to account for their chromospheric temperature structure.

scholarly journals Heating and dynamics of the quiet solar chromosphere

2007 ◽  
Vol 3 (S247) ◽  
pp. 93-98
Author(s):  
Wolfgang Kalkofen
Keyword(s):  
Acoustic Waves ◽  
Energy Exchange ◽  
Spatial Scales ◽  
Quantitative Measure ◽  
Hydrodynamical Model ◽  
Radiative Energy ◽  
Solar Chromosphere ◽  
Spatial Averaging ◽  
Heating Mechanism ◽  
Open Question

AbstractThe quiet solar chromosphere in regions with negligible magnetic field is believed to be heated by acoustic waves. But their energy flux, measured in the upper photosphere with the Transition Region And Coronal Explorer (TRACE), has been found to be insufficient to account for the radiative emission from the chromosphere. Wedemeyer-Böhm et al. (2007) and Cuntz et al. (2007), employing a 3D hydrodynamical model by Wedemeyer et al. (2004), have proposed that the spatial resolution of TRACE is inadequate to resolve intensity fluctuations that occur on small spatial scales. This paper accepts the principle of spatial averaging by TRACE as a qualitative explanation for the low acoustic flux but finds that the hydrodynamical model is too much simplified in the treatment of radiative energy exchange to provide a quantitative measure of the suppression of the fluctuations. The heating mechanism of the chromosphere thus remains an open question.

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