Benchmarking Fast-to-Alfvén Mode Conversion in a Cold MHD Plasma. Ii. How to Get Alfvén Waves Through the Solar Transition Region

Hansen, Shelley Candice; Cally, Paul Stuart

doi:10.1088/0004-637x/751/1/31

Cited by 47 publications

(35 citation statements)

References 48 publications

(80 reference statements)

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“…The MBPs under study here do have small magnetic field inclinations with respect to the lineofsight (with an average value of 9 ± 4°), similar to those studied by Jafarzadeh et al (2014). If the reflection point of fast waves reaches the transition region, up to 30% of the fast wave's energy flux can be carried across the transition region by the Alfvén waves due to the fast-to-Alfvén mode conversion (Hansen & Cally 2012). Thus, fast waves may contribute to the heating of the outer atmospheric layers.…”

Section: Comparisons and Discussionsupporting

confidence: 67%

High-frequency Oscillations in Small Magnetic Elements Observed with Sunrise/SuFI

Jafarzadeh¹,

Solanki²,

Stangalini³

et al. 2017

ApJS

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We characterize waves in small magnetic elements and investigate their propagation in the lower solar atmosphere from observations at high spatial and temporal resolution. We use the wavelet transform to analyze oscillations of both horizontal displacement and intensity in magnetic bright points found in the 300nm and the CaIIH 396.8nm passbands of the filter imager on board the SUNRISE balloon-borne solar observatory. Phase differences between the oscillations at the two atmospheric layers corresponding to the two passbands reveal upward propagating waves at high frequencies (up to 30 mHz). Weak signatures of standing as well as downward propagating waves are also obtained. Both compressible and incompressible (kink) waves are found in the smallscale magnetic features. The two types of waves have different, though overlapping, period distributions. Two independent estimates give a height difference of approximately 450±100km between the two atmospheric layers sampled by the employed spectral bands. This value, together with the determined short travel times of the transverse and longitudinal waves provide us with phase speeds of 29±2km s −1 and 31±2km s −1 , respectively. We speculate that these phase speeds may not reflect the true propagation speeds of the waves. Thus, effects such as the refraction of fast longitudinal waves may contribute to an overestimate of the phase speed.

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Section: Comparisons and Discussionsupporting

confidence: 67%

High-frequency Oscillations in Small Magnetic Elements Observed with Sunrise/SuFI

Jafarzadeh¹,

Solanki²,

Stangalini³

et al. 2017

ApJS

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“…Indeed, observations suggest that Alfvénic-type waves can carry sufficient energy to heat the solar atmosphere and accelerate the solar wind (see, e.g., De Pontieu et al 2007;Tomczyk et al 2007;McIntosh et al 2011;Hahn & Savin 2014). However, there are still many open questions under debate, e.g., the source of excitation or driver of the waves (e.g., Fedun et al 2011a;Morton et al 2013;Mumford et al 2015), the reflection and transmission properties of the waves as they propagate through the various atmospheric layers (e.g., Hollweg 1978;Leroy 1980;Similon & Zargham 1992;Cranmer & van Ballegooijen 2005), the conversion and coupling between the different MHD wave modes (e.g., Hansen & Cally 2012;Khomenko & Cally 2012), and the physical mechanisms that may lead to the efficient dissipation of wave energy (e.g., Khodachenko et al 2004;Antolin & Shibata 2010;Goodman 2011;van Ballegooijen et al 2011;Tu & Song 2013;Soler et al 2015b;Arber et al 2016), to name a few.…”

Section: Introductionmentioning

confidence: 99%

Propagation of Torsional Alfvén Waves from the Photosphere to the Corona: Reflection, Transmission, and Heating in Expanding Flux Tubes

Soler

Terradas

Oliver

et al. 2017

ApJ

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It has been proposed that Alfvén waves play an important role in the energy propagation through the solar atmospheric plasma and its heating. Here we theoretically investigate the propagation of torsional Alfvén waves in magnetic flux tubes expanding from the photosphere up to the low corona and explore the reflection, transmission, and dissipation of wave energy. We use a realistic variation of the plasma properties and the magnetic field strength with height. Dissipation by ion-neutral collisions in the chromosphere is included using a multifluid partially ionized plasma model. Considering the stationary state, we assume that the waves are driven below the photosphere and propagate to the corona, while they are partially reflected and damped in the chromosphere and transition region. The results reveal the existence of three different propagation regimes depending on the wave frequency: low frequencies are reflected back to the photosphere, intermediate frequencies are transmitted to the corona, and high frequencies are completely damped in the chromosphere. The frequency of maximum transmissivity depends on the magnetic field expansion rate and the atmospheric model, but is typically in the range of 0.04-0.3Hz. Magnetic field expansion favors the transmission of waves to the corona and lowers the reflectivity of the chromosphere and transition region compared to the case with a straight field. As a consequence, the chromospheric heating due to ion-neutral dissipation systematically decreases when the expansion rate of the magnetic flux tube increases.

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“…Fast magnetic waves are generated from the conversion of acoustic waves at the region where the sound and Alfvén speed are similar (Schunker & Cally 2006). These waves are reflected back to the photosphere due to the gradient in the Alfvén speed (Khomenko & Collados 2006), or are partially converted into upgoing and downgoing Alfvén waves (Hansen & Cally 2012;Khomenko & Cally 2012;Felipe 2012). Downward propagating fast and Alfvén waves may leave a trace on the travel-time perturbations measured from local helioseismology techniques (Cally & Moradi 2013).…”

Section: Introductionmentioning

confidence: 99%

Helioseismic Holography of Simulated Sunspots: Magnetic and Thermal Contributions to Travel Times

Felipe

Braun

Crouch

et al. 2016

ApJ

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Wave propagation through sunspots involves conversion between waves of acoustic and magnetic character. In addition, the thermal structure of sunspots is very different than that of the quiet Sun. As a consequence, the interpretation of local helioseismic measurements of sunspots has long been a challenge. With the aim of understanding these measurements, we carry out numerical simulations of wave propagation through sunspots. Helioseismic holography measurements made from the resulting simulated wavefields show qualitative agreement with observations of real sunspots. We use additional numerical experiments to determine, separately, the influence of the thermal structure of the sunspot and the direct effect of the sunspot magnetic field. We use the ray approximation to show that the travel-time shifts in the thermal (non-magnetic) sunspot model are primarily produced by changes in the wave path due to the Wilson depression rather than variations in the wave speed. This shows that inversions for the subsurface structure of sunspots must account for local changes in the density. In some ranges of horizontal phase speed and frequency there is agreement (within the noise level in the simulations) between the travel times measured in the full magnetic sunspot model and the thermal model. If this conclusion proves to be robust for a wide range of models, it would suggest a path towards inversions for sunspot structure.

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Benchmarking Fast-to-Alfvén Mode Conversion in a Cold MHD Plasma. Ii. How to Get Alfvén Waves Through the Solar Transition Region

Cited by 47 publications

References 48 publications

High-frequency Oscillations in Small Magnetic Elements Observed with Sunrise/SuFI

High-frequency Oscillations in Small Magnetic Elements Observed with Sunrise/SuFI

Propagation of Torsional Alfvén Waves from the Photosphere to the Corona: Reflection, Transmission, and Heating in Expanding Flux Tubes

Helioseismic Holography of Simulated Sunspots: Magnetic and Thermal Contributions to Travel Times

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