Combined helioseismic inversions for 3D vector flows and sound-speed perturbations

Korda, David; Švanda, Michal

doi:10.1051/0004-6361/201833000

Cited by 10 publications

(12 citation statements)

References 30 publications

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“…These travel times were then inverted for flows using multichannel subtractive optimally localised averaging method (MC-SOLA; see Jackiewicz et al 2012) when involving the cross-talk minimisation (Švanda et al 2011;Korda & Švanda 2019). When discussing the flows, thanks to the cross-talk minimisation our methodology allows one to not only infer the horizontal velocities (v x in the zonal direction and v y in the meridional direction), but also the vertical component v z .…”

Section: Observations and Simulationmentioning

confidence: 99%

Photospheric downflows observed with SDO/HMI, HINODE, and an MHD simulation

Roudier

Švanda

Malherbe

et al. 2021

A&A

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Downflows on the solar surface are suspected to play a major role in the dynamics of the convection zone, at least in its outer part. We investigate the existence of the long-lasting downflows whose effects influence the interior of the Sun but also the outer layers. We study the sets of Dopplergrams and magnetograms observed with Solar Dynamics Observatory and Hinode spacecrafts and an magnetohydrodynamic (MHD) simulation. All of the aligned sequences, which were corrected from the satellite motions and tracked with the differential rotation, were used to detect the long-lasting downflows in the quiet-Sun at the disc centre. To learn about the structure of the flows below the solar surface, the time-distance local helioseismology was used. The inspection of the 3D data cube (x, y, t) of the 24 h Doppler sequence allowed us to detect 13 persistent downflows. Their lifetimes lie in the range between 3.5 and 20 h with a sizes between 2″ and 3″ and speeds between −0.25 and −0.72 km s−1. These persistent downflows are always filled with the magnetic field with an amplitude of up to 600 Gauss. The helioseismic inversion allows us to describe the persistent downflows and compare them to the other (non-persistent) downflows in the field of view. The persistent downflows seem to penetrate much deeper and, in the case of a well-formed vortex, the vorticity keeps its integrity to the depth of about 5 Mm. In the MHD simulation, only sub-arcsecond downflows are detected with no evidence of a vortex comparable in size to observations at the surface of the Sun. The long temporal sequences from the space-borne allows us to show the existence of long-persistent downflows together with the magnetic field. They penetrate inside the Sun but are also connected with the anchoring of coronal loops in the photosphere, indicating a link between downflows and the coronal activity. A links suggests that EUV cyclones over the quiet Sun could be an effective way to heat the corona.

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Section: Observations and Simulationmentioning

confidence: 99%

Photospheric downflows observed with SDO/HMI, HINODE, and an MHD simulation

Roudier

Švanda

Malherbe

et al. 2021

A&A

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“…The RMS of the maps inverted by our method is smaller than that from JSOC. This discrepancy may be explained as an action of the cross-talk with flows, as demonstrated recently using synthetic data (Korda & Švanda 2019). Random-noise levels are also very important in the inversions for the sound-speed perturbations.…”

Section: Discussionmentioning

confidence: 75%

“…In other words, the averaging kernels describe an area where the inversion is sensitive to the considered quantities. The implementation of this method is described in detail by Korda & Švanda (2019). It can be seen from Eq.…”

Section: The Sola Methodsmentioning

confidence: 99%

“…The significant correlation and larger RMS of the JSOC inversion than of our inversion together with a very similar localisation in the Sun is consistent with the JSOC inversions being contaminated by the positively correlated cross-talk from the other quantities. Korda & Švanda (2019) found that the cross-talk may consist of about one half of the inverted estimate in the case of the inversions for the sound speed. The differences in RMS might be explained by such cross-talk contamination.…”

Section: Jsoc-like Targetmentioning

confidence: 99%

“…In the captions of the figures, this case is labelled OUR2. Except for the selection of the target, the inversion is principally the same as described by Korda & Švanda (2019).…”

Section: Our Inversionsmentioning

confidence: 99%

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Comparison of time–distance inversion methods applied to SDO/HMI Dopplergrams

Korda

Švanda

Zhao

2019

A&A

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Context. The Helioseismic and Magnetic Imager (HMI) onboard the Solar Dynamics Observatory (SDO) satellite has been observing the Sun since 2010. The uninterrupted series of Dopplergrams are ideal for studying the dynamics of the upper solar convection zone. Within the Joint Science Operations Center (JSOC) the time-distance inversions for flows and sound-speed perturbations were introduced. The automatic pipeline has produced flow and sound-speed maps every 8 hours. We verify the results of JSOC inversions by comparing the data products to equivalent results from inverse modelling obtained by an independent inversion pipeline. Aims. We compared the results from the JSOC pipeline for horizontal flow components and the perturbations of the speed of sound at set of depths with equivalent results from an independently implemented pipeline using a different time-distance inversion scheme. Our inversion pipeline allows inversion for all quantities at once while allowing minimisation of the crosstalk between them. This gives us an opportunity to discuss the possible biases present in the JSOC data products. Methods. For the tests we used the subtractive optimally localised averaging (SOLA) method with a minimisation of the cross-talk. We compared three test inversions for each quantity at each target depth. At first, we used the JSOC setup to reproduce the JSOC results. Subsequently, we used the extended pipeline to improve these results by incorporating more independent travel-time measurements but keeping the JSOC-indicated localisation in the Sun. Finally, we inverted for flow components and sound-speed perturbations using a localisation kernel with properties advertised in the JSOC metadata. Results. We successfully reproduced the horizontal flow components. The sound-speed perturbations are strongly affected by the high level of the cross-talk in JSOC products. This leads to larger amplitudes in the inversions for the sound-speed perturbations. Different results were obtained when a target function localised around the target depth was used. This is a consequence of non-localised JSOC averaging kernels. We add that our methodology also allows inversion for the vertical flow. cuses on local perturbations of the Sun with respect to the reference model (Lindsey et al. 1993). Furthermore, local helioseismology has been successfully used in many research studies (see a review by Gizon et al. 2010). Time-distance helioseismologyOne of the local-helioseismic approaches is the time-distance method (Duvall et al. 1993) which is a set of tools devoted to measuring, studying, and interpreting travel times of the waves travelling through the sub-surface layers of the solar convection zone. These waves are randomly excited via vigorous convection near the surface and as they propagate throughout the solar interior, their propagation speeds and paths are affected by deeper anomalies, for example anomalies in density, sound speed, temperature, and plasma flows.The signatures of travelling waves are observed as timedomain oscilla...

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