Local helioseismology using ring diagram analysis

Antia, H. M.; Basu, Sarbani

doi:10.1002/asna.200610727

Cited by 17 publications

(19 citation statements)

References 44 publications

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“…Fourier-Hankel analysis was developed to study the relationship between ingoing and outgoing waves around a sunspot (Braun et al 1987;Braun 1995). Ring-diagram analysis consists of analysing the frequencies of solar acoustic waves over small patches of the solar surface (Hill 1988;Antia and Basu 2007). Time-distance helioseismology (TD) measures the travel times of wave packets moving through the solar interior (Duvall Jr. et al 1993).…”

Section: Introductionmentioning

confidence: 99%

“…, Duvall Jr. et al 1996;Jensen et al 2001;Kosovichev et al 2000;Zhao et al 2001;Couvidat et al 2006). Ring-diagram analysis has a coarser horizontal resolution and is used to study the subsurface structure of entire active regions (e.g., Basu et al 2004;Antia and Basu 2007;Bogart et al 2008). While these methods and their variants appear to be quite robust, it has not been demonstrated that they are consistent.…”

Section: Introductionmentioning

confidence: 99%

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Helioseismology of Sunspots: A Case Study of NOAA Region 9787

et al. 2008

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Various methods of helioseismology are used to study the subsurface properties of the sunspot in NOAA Active Region 9787. This sunspot was chosen because it is axisymmetric, shows little evolution during 20-28 January 2002, and was observed continuously by the MDI/SOHO instrument. AR 9787 is visible on helioseismic maps of the farside of the Sun from 15 January, i.e. days before it crossed the East limb.Oscillations have reduced amplitudes in the sunspot at all frequencies, whereas a region of enhanced acoustic power above 5.5 mHz (above the quiet-Sun acoustic cutoff) is seen outside the sunspot and the plage region. This enhanced acoustic power has been suggested to be caused by the conversion of acoustic waves into magneto-acoustic waves that are refracted back into the interior and re-emerge as acoustic waves in the quiet Sun. Observations show that the sunspot absorbs a significant fraction of the incoming p and f modes around 3 mHz. A numerical simulation of MHD wave propagation through a simple model of AR 9787 confirmed that wave absorption is likely to be due to the partial conversion of incoming waves into magneto-acoustic waves that propagate down the sunspot. Wave travel times and mode frequencies are affected by the sunspot. In most cases, wave packets that propagate through the sunspot have reduced travel times. At short travel distances, however, the sign of the travel-time shifts appears to depend sensitively on how the data are processed and, in particular, on filtering in frequency-wavenumber space. We carry out two linear inversions for wave speed: one using travel-times and phase-speed filters and the other one using mode frequencies from ring analysis. These two inversions give subsurface wave-speed profiles with opposite signs and different amplitudes.The travel-time measurements also imply different subsurface flow patterns in the surface layer depending on the filtering procedure that is used. Current sensitivity kernels are unable to reconcile these measurements, perhaps because they rely on imperfect models of the power spectrum of solar oscillations. We present a linear inversion for flows of ridge-filtered travel times. This inversion shows a horizontal outflow in the upper 4 Mm that is consistent with the moat flow deduced from the surface motion of moving magnetic features.From this study of AR 9787, we conclude that we are currently unable to provide a unified description of the subsurface structure and dynamics of the sunspot.

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Section: Introductionmentioning

confidence: 99%

Section: Introductionmentioning

confidence: 99%

Helioseismology of Sunspots: A Case Study of NOAA Region 9787

et al. 2008

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“…There have been such studies with data that cover only a part of the solar cycle (Chou & Dai 2001;Haber et al 2002;Basu & Antia 2003;González Hernández et al 2006Zaatri et al 2006;etc.). All these studies have found significant temporal variations in the meridional flows, though they are not always in complete agreement with each other (see Antia & Basu 2007). Among the results that stand out is that the meridional flow speed is slower at maximum activity than at the minimum (Chou & Dai 2001;subsequently confirmed by Hathaway & Rightmire 2010).…”

Section: Introductionmentioning

confidence: 91%

Characteristics of Solar Meridional Flows During Solar Cycle 23

Basu

Antia

2010

ApJ

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We have analyzed available full-disc data from the Michelson Doppler Imager (MDI) on board SoHO using the "ring diagram" technique to determine the behavior of solar meridional flows over solar cycle 23 in the outer 2% of the solar radius. We find that the dominant component of meridional flows during solar maximum was much lower than that during the minima at the beginning of cycles 23 and 24. There were differences in the flow velocities even between the two minima. The meridional flows show a migrating pattern with highervelocity flows migrating towards the equator as activity increases. Additionally, we find that the migrating pattern of the meridional flow matches those of sunspot butterfly diagram and the zonal flows in the shallow layers. A high latitude band in meridional flow appears around 2004, well before the current activity minimum. A Legendre polynomial decomposition of the meridional flows shows that the latitudinal pattern of the flow was also different during the maximum as compared to that during the two minima. The different components of the flow have different time-dependences, and the dependence is different at different depths.

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“…These travel times are measured from the temporal cross-covariances between the Doppler observations at pairs of points on the solar surface (see Gizon & Birch 2005, for a review). Ring-diagram analysis (Hill 1988;Antia & Basu 2007) measures the Doppler shift of acoustic and surface-gravity oscillation modes in the local power spectra and uses these Doppler shifts to infer local flows in the solar interior. To compute the local power spectra, the solar surface is divided into a number of spatial tiles.…”

Section: Introductionmentioning

confidence: 99%

An improved multi-ridge fitting method for ring-diagram helioseismic analysis

Nagashima

Birch

Schou

et al. 2020

A&A

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Context. There is a wide discrepancy in current estimates of the strength of convection flows in the solar interior obtained using different helioseismic methods applied to observations from the Helioseismic and Magnetic Imager (HMI) onboard the Solar Dynamics Observatory (SDO). The cause for these disparities is not known. Aims. As one step in the effort to resolve this discrepancy, we aim to characterize the multi-ridge fitting code for ring-diagram helioseismic analysis that is used to obtain flow estimates from local power spectra of solar oscillations. Methods. We updated the multi-ridge fitting code developed by Greer et al. (2014, Sol. Phys., 289, 2823 to solve several problems we identified through our inspection of the code. In particular, we changed the 1) merit function to account for the smoothing of the power spectra, 2) model for the power spectrum, and 3) noise estimates. We used Monte Carlo simulations to generate synthetic data and to characterize the noise and bias of the updated code by fitting these synthetic data.Results. The bias in the output fit parameters, apart from the parameter describing the amplitude of the p-mode resonances in the power spectrum, is below what can be measured from the Monte-Carlo simulations. The amplitude parameters are underestimated; this is a consequence of choosing to fit the logarithm of the averaged power. We defer fixing this problem as it is well understood and not significant for measuring flows in the solar interior. The scatter in the fit parameters from the Monte-Carlo simulations is well-modeled by the formal error estimates from the code. Conclusions. We document and demonstrate a reliable multi-ridge fitting method for ring-diagram analysis. The differences between the updated fitting results and the original results are less than one order of magnitude and therefore we suspect that the changes will not eliminate the aforementioned orders-of-magnitude discrepancy in the amplitude of convective flows in the solar interior. Key words. Sun: helioseismology -Methods: data analysis Schou et al. 2012) onboard the Solar Dynamics Observatory (SDO; Pesnell et al. 2012) are automatically computed by the SDO/HMI ring-diagram pipeline (Bogart et al. 2011a,b) on a daily basis since the SDO launch in 2010.The HMI ring pipeline codes separately fit each single ridge (single radial order n) in the power in slices at constant horizontal wavenumber or slices in temporal frequency. Greer et al. (2014) developed an alternative approach based on simultaneously fitting multiple ridges (multiple radial orders) at each horizontal wavenumber. Greer et al. (2015) introduced another in-Article number, page 1 of 18

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Local helioseismology using ring diagram analysis

Cited by 17 publications

References 44 publications

Helioseismology of Sunspots: A Case Study of NOAA Region 9787

Helioseismology of Sunspots: A Case Study of NOAA Region 9787

Characteristics of Solar Meridional Flows During Solar Cycle 23

An improved multi-ridge fitting method for ring-diagram helioseismic analysis

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