Acoustic waves in the solar atmosphere at high spatial resolution

González, N. Bello; Soriano, M. Flores; Kneer, F.; Okunev, O.

doi:10.1051/0004-6361/200912275

Cited by 48 publications

(65 citation statements)

References 45 publications

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“…The number of about 10 kW m −2 falls in line with the energy fluxes between 3 to 12 kW m −2 at a height of about 250 km determined from velocity oscillations in, e.g. Bello González et al (2009González et al ( , 2010 or Malherbe et al (2012;MA12). The latter authors also determined the total energy contained in what they call "acoustic events", i.e.…”

Section: Energy Content Of Bright Grains and Related Energy Fluxsupporting

confidence: 77%

The energy of waves in the photosphere and lower chromosphere

Beck

Rezaei

Puschmann

2013

A&A

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Context. Most semi-empirical static one-dimensional (1D) models of the solar atmosphere in the magnetically quiet Sun (QS) predict an increase in temperature at chromospheric layers. Numerical simulations of the solar chromosphere with a variable degree of sophistication, i.e. from 1D to three-dimensional (3D) simulations; assuming local thermal equilibrium (LTE) or non-LTE (NLTE), on the other hand, only yielded an increase in the brightness temperature without any stationary increase in the gas temperature.Aims. We investigate the thermal structure in the solar chromosphere as derived from an LTE inversion of observed Ca ii H spectra in QS and active regions (ARs).Methods. We applied an inversion strategy based on the SIR (Stokes inversion by response functions) code to Ca ii H spectra to obtain 1D temperature stratifications. We investigated the temperature stratifications on differences between magnetic and field-free regions in the QS, and on differences between QS and ARs. We determined the energy content of individual calcium bright grains (BGs) as specific candidates of chromospheric heating events. We compared observed with synthetic NLTE spectra to estimate the significance of the LTE inversion results. Results. The fluctuations of observed intensities yield a variable temperature structure with spatio-temporal rms fluctuations below 100 K in the photosphere and between 200 and 300 K in the QS chromosphere. The average temperature stratification in the QS does not exhibit a clear chromospheric temperature rise, unlike the AR case. We find a characteristic energy content of about 7 × 10 18 J for BGs that repeat with a cadence of about 160 s. The precursors of BGs have a vertical extent of about 200 km and a horizontal extent of about 1 Mm. The comparison of observed with synthetic NLTE profiles partly confirms the results of the LTE inversion that the solar chromosphere in the QS oscillates between an atmosphere in radiative equilibrium and one with a moderate chromospheric temperature rise. Two-dimensional x − z temperature maps exhibit nearly horizontal canopy-like structures with an extent of a few Mm around photospheric magnetic field concentrations at a height of about 600 km. Conclusions. The large difference between QS regions and ARs and the better match of AR and NLTE reference spectra suggest that magnetic heating processes are more important than commonly assumed. The temperature fluctuations in QS derived by the LTE inversion do not suffice on average to maintain a stationary chromospheric temperature rise. The spatially and vertically resolved information on the temperature structure allows one to investigate in detail the topology and evolution of the thermal structure in the lower solar atmosphere.

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Section: Energy Content Of Bright Grains and Related Energy Fluxsupporting

confidence: 77%

The energy of waves in the photosphere and lower chromosphere

Beck

Rezaei

Puschmann

2013

A&A

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“…2), their characteristic similarities and differences from RPWs, and the possible reconstruction of the magnetic field topology using the wave characteristics in sunspots. To verify the existence of photospheric RPWs, we suggest further observations with high spatial and temporal resolution using photospheric spectral lines that are magnetic insensitive (with a Landé-factor g = 0), for example Fe  557.6 nm (Bello González et al 2009) or Fe  543.4 nm (Bello González et al 2010). For the latter, we have also found RPW signatures.…”

Section: Discussionmentioning

confidence: 70%

Signatures of running penumbral waves in sunspot photospheres

Löhner-Böttcher¹,

González²

2015

A&A

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Context. The highly dynamic atmosphere above sunspots exhibits a wealth of magnetohydrodynamic waves. Recent studies suggest a coupled nature of the most prominent phenomena: umbral flashes and running penumbral waves (RPWs). Aims. From an observational point of view, we perform a height-dependent study of RPWs, compare their wave characteristics, and aim to track down these so far only chromospherically observed phenomena to photospheric layers to prove the upward propagating field-guided nature of RPWs. Methods. We analyze a time series (58 min) of multiwavelength observations of an isolated circular sunspot (NOAA11823) taken at high spatial and temporal resolution in spectroscopic mode with the Interferometric BIdimensional Spectro-polarimeter (IBIS/DST). By means of a multilayer intensity sampling, velocity comparisons, wavelet power analysis, and sectorial studies of time slices, we retrieve the power distribution, characteristic periodicities, and propagation characteristics of sunspot waves at photospheric and chromospheric levels. Results. Signatures of RPWs are found at photospheric layers. Those continuous oscillations occur preferably at periods between 4-6 min starting at the inner penumbral boundary. The photospheric oscillations all have a slightly delayed, more defined chromospheric counterpart with larger relative velocities, which are linked to preceding umbral flash events. In all of the layers, the power of RPWs follows a filamentary fine-structure and shows a typical ring-shaped power distribution increasing in radius for larger wave periods. The analysis of time slices reveals apparent horizontal velocities for RPWs at photospheric layers of ≈51 km s −1 , which decrease to ≈37 km s −1 at chromospheric heights. Conclusions. The observations strongly support the scenario of RPWs being upward propagating slow-mode waves guided by the magnetic field lines. Clear evidence for RPWs at photospheric layers is given. The inverse proportionality of the peak period and cutoff period on the field inclination is supported by the observations. The larger apparent horizontal velocities at photospheric heights hint at the more horizontal penumbral field inclination.

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“…This is mainly due to the missing information about waves with frequencies higher than 9.6 mHz and the unknown transfer function TF (ν) in the chromosphere that we set to one. Fossum & Carlsson (2006) and Bello González et al (2009González et al ( , 2010 studied the propagation of acoustic waves in quiet regions and from their results it follows that the relative contribution of waves with frequencies larger than 10 mHz is of about 50-100 % of the acoustic flux measured in the range 5-10 mHz. On the other hand, our results indicate that in active regions, this relative contribution probably decreases with increasing activity, from model VAL D to FAL H (Sect.…”

Section: Discussionmentioning

confidence: 99%

Chromospheric Heating by Acoustic Waves Compared to Radiative Cooling

Sobotka

Heinzel

Švanda

et al. 2016

ApJ

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Acoustic and magnetoacoustic waves are among the possible candidate mechanisms that heat the upper layers of solar atmosphere. A weak chromospheric plage near a large solar pore NOAA 11005 was observed on October 15, 2008 in the lines Fe I 617.3 nm and Ca II 853.2 nm with the Interferometric Bidimemsional Spectrometer (IBIS) attached to the Dunn Solar Telescope. Analyzing the Ca II observations with spatial and temporal resolutions of 0. ′′ 4 and 52 s, the energy deposited by acoustic waves is compared with that released by radiative losses. The deposited acoustic flux is estimated from power spectra of Doppler oscillations measured in the Ca II line core. The radiative losses are calculated using a grid of seven 1D hydrostatic semi-empirical model atmospheres. The comparison shows that the spatial correlation of maps of radiative losses and acoustic flux is 72 %. In quiet chromosphere, the contribution of acoustic energy flux to radiative losses is small, only of about 15 %. In active areas with photospheric magnetic field strength between 300 G and 1300 G and inclination of 20 • -60 • , the contribution increases from 23 % (chromospheric network) to 54 % (a plage). However, these values have to be considered as lower limits and it might be possible that the acoustic energy flux is the main contributor to the heating of bright chromospheric network and plages.

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Acoustic waves in the solar atmosphere at high spatial resolution

Cited by 48 publications

References 45 publications

The energy of waves in the photosphere and lower chromosphere

The energy of waves in the photosphere and lower chromosphere

Signatures of running penumbral waves in sunspot photospheres

Chromospheric Heating by Acoustic Waves Compared to Radiative Cooling

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