MHD wave transmission in the Sun’s atmosphere

Stangalini, M.; Moro, D. Del; Berrilli, F.; Jefferies, S. M.

doi:10.1051/0004-6361/201117356

Cited by 60 publications

(69 citation statements)

References 25 publications

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“…The cutoff frequency can also be lowered by the socalled ramp effect, allowing the propagation of low frequency waves in an inclined magnetic field environment (Jefferies et al 2006). Stangalini et al (2011) found, using the same IBIS data investigated in this work, that the amount of energy transferred toward the upper layers of the Sun depends strongly on the complexity of the magnetic field geometry, through a combination of ramp effect and MHD mode conversion. In addition to this, many authors have reported suspicious high-frequency power enhancements in rings surrounding active regions, both in the photosphere (Brown et al 1992) and the chromosphere (Braun et al 1992).…”

Section: Introductionmentioning

confidence: 53%

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Three-minute wave enhancement in the solar photosphere

Stangalini

Giannattasio

Moro

et al. 2012

A&A

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It is a well-known result that the power of five-minute oscillations is progressively reduced by magnetic fields in the solar photosphere. Many authors have pointed out that this could be due to a complex interaction of many processes: opacity effects, MHD mode conversion, and intrinsically weaker acoustic emissivity in strong magnetic fields. While five-minute oscillations predominate in the photosphere, it has been shown that in the chromosphere three-minute oscillations are more common. Two main theories have been proposed to explain the presence of the latter oscillations based upon resonance filtering in the atmospheric cavity and non-linear interactions. In this work, we show, through the analysis of IBIS observations of a solar pore in the photospheric Fe I 617.3 nm line, that three-minute waves are already present at the height of formation of this line, their amplitude depends on the magnetic field strength, and they are strictly confined to the umbral region.

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Section: Introductionmentioning

confidence: 53%

“…For further details of the data set and the calibration pipeline, we refer to Stangalini et al (2011) and Viticchié et al (2009) respectively.…”

Section: Observationsmentioning

confidence: 99%

Three-minute wave enhancement in the solar photosphere

Stangalini

Giannattasio

Moro

et al. 2012

A&A

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“…Projection effects and the ramp effect should be taken into account in order to compare the transmission coefficient with the observations. To this end, we follow the approach proposed by Stangalini et al (2011) and calculate the modified transmission coefficient:…”

Section: Discussionmentioning

confidence: 99%

“…We use the twodimensional model proposed by Schunker & Cally (2006) and Cally (2007) and the modifications proposed by Stangalini et al (2011) (see Sect. 3).…”

Section: Transmission and Conversion Of Waves On The Magnetic Canopymentioning

confidence: 99%

Transmission and conversion of magnetoacoustic waves on the magnetic canopy in a quiet Sun region

Kontogiannis

Tsiropoula

Tziotziou

2014

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Context. We present evidence for the conversion and transmission of wave modes on the magnetic flux tubes that constitute mottles and form the magnetic canopy in a quiet Sun region. Aims. Our aim is to highlight the details and the key parameters of the mechanism that produces power halos and magnetic shadows around the magnetic network observed in Hα. Methods. We use our previous calculations of the magnetic field vector and the height of the magnetic canopy, and based on simple assumptions, we determine the turning height, i.e., the height at which the fast magnetoacoustic waves reflect at the chromosphere. We compare the variation of 3, 5, and 7 min power in the magnetic shadow and the power halo with the results of a two-dimensional model on mode conversion and transmission. The key parameter of the model is the attack angle, which is related to the inclination of the magnetic field vector at the canopy height. Our analysis takes also into account that 1) there are projection effects on the propagation of waves; 2) the magnetic canopy and the turning height are curved layers; 3) waves with periods longer than 3 min only reach the chromosphere in the presence of inclined magnetic fields (ramp effect); 4) mottles in Hα are canopy structures; and 5) the wings of Hα contain mixed signal from low-and high-β plasma.Results. The dependence of the measured power on the attack angle follows the anticipated by the two-dimensional model very well. Long-period slow waves are channeled to the upper chromospheric layers following the magnetic field lines of mottles, while shortperiod fast waves penetrate the magnetic canopy and are reflected back higher, at the turning height. Conclusions. Although both magnetoacoustic modes contribute to velocity signals, making the interpretation of observations a challenging task, we conclude that conversion and transmission of the acoustic waves into fast and slow magnetoacoustic waves are responsible for forming power halos and magnetic shadows in the quiet Sun region.

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“…This feature had developed a visible penumbra during days preceding our observations and should be therefore classified as naked spot. Nevertheless, for consistency with previous studies that have investigated the physical properties of this same feature (Stangalini et al 2012;Sobotka et al 2012), we will address it as a pore in the following. This choice is also motivated by the fact that the magnetic field of the structure does not exceed 2000 G (see Sect.…”

Section: Introductionmentioning

confidence: 98%

High cadence spectropolarimetry of moving magnetic features observed around a pore

Criscuoli

Moro

Giannattasio

et al. 2012

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Context. Moving magnetic features (MMFs) are small-size magnetic elements that are seen to stream out from sunspots, generally during their decay phase. Several observational results presented in the literature suggest them to be closely related to magnetic filaments that extend from the penumbra of the parent spot. Nevertheless, few observations of MMFs streaming out from spots without penumbra have been reported. The literature still lacks analyses of the physical properties of these features. Aims. We investigate physical properties of monopolar MMFs observed around a small pore that had developed penumbra in the days preceding our observations and compare our results with those reported in the literature for features observed around sunspots.Methods. We analyzed NOAA 11005 during its decay phase with data acquired at the Dunn Solar Telescope in the Fe i 617.3 nm and the Ca ii 854.2 nm spectral lines with IBIS, and in the G-band. The field of view showed monopolar MMFs of both polarities streaming out from the leading negative polarity pore of the observed active region. Combining different analyses of the data, we investigated the temporal evolution of the relevant physical quantities associated with the MMFs as well as the photospheric and chromospheric signatures of these features. Results. We show that the characteristics of the investigated MMFs agree with those reported in the literature for MMFs that stream out from spots with penumbrae. Moreover, observations of at least two of the observed features suggest them to be manifestations of emerging magnetic arches.

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MHD wave transmission in the Sun’s atmosphere

Cited by 60 publications

References 25 publications

Three-minute wave enhancement in the solar photosphere

Three-minute wave enhancement in the solar photosphere

Transmission and conversion of magnetoacoustic waves on the magnetic canopy in a quiet Sun region

High cadence spectropolarimetry of moving magnetic features observed around a pore

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