Meridional Flow in the Solar Convection Zone. I. Measurements From Gong Data

Kholikov, S.; Serebryanskiy, A.; Jackiewicz, Jason

doi:10.1088/0004-637x/784/2/145

Cited by 50 publications

(46 citation statements)

References 37 publications

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“…Above and below this layer, the flows are mostly poleward, indicating a doublecell circulation in both hemispheres. Following a similar analysis procedure but using GONG observations, Kholikov et al (2014) and Jackiewicz et al (2015) reported that the poleward flow turns to equatorward at about the same depth as reported by Zhao et al (2013) but did not find a persistent poleward flow beneath the layer of equatorward flow. Later, through inverting timedistance measurements that are obtained from the HMI's 4 years continuous observations, with the radial flow component included and a mass-conservation condition applied, Rajaguru & Antia (2015) reported that the equatorward flow was found only beneath 0.77 R ⊙ , consistent with a single-cell circulation.…”

Section: Introductionmentioning

confidence: 75%

A Comprehensive Method to Measure Solar Meridional Circulation and the Center-to-limb Effect Using Time–Distance Helioseismology

Chen

Zhao

2017

ApJ

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Meridional circulation is a crucial component of the Sun's internal dynamics, but its inference in the deep interior is complicated by a systematic center-to-limb effect in helioseismic measurement techniques. Previously, an empirical method, removing travel-time shifts measured for east-west traveling waves in the equatorial area from those measured for north-south traveling waves in the central meridian area, was used, but its validity and accuracy need to be assessed. Here we develop a new method to separate the center-to-limb effect, δτ CtoL , and meridional-flow-induced travel-time shifts, δτ MF , in a more robust way. Using 7-yr observations of the SDO/HMI, we exhaustively measure travel-time shifts between two surface locations along the solar disk's radial direction for all azimuthal angles and all skip distances. The measured travel-time shifts are a linear combination of δτ CtoL and δτ MF , which can be disentangled through solving the linear equation set. The δτ CtoL is found isotropic relative to the azimuthal angle, and the δτ MF are then inverted for the meridional circulation. Our inversion results show a three-layer flow structure, with equatorward flow found between about 0.82 and 0.91 R ⊙ for low latitude areas and between about 0.85 and 0.91 R ⊙ for higher latitude areas. Poleward flows are found below and above the equatorward flow zones, indicating a double-cell circulation in each hemisphere.

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Section: Introductionmentioning

confidence: 75%

A Comprehensive Method to Measure Solar Meridional Circulation and the Center-to-limb Effect Using Time–Distance Helioseismology

Chen

Zhao

2017

ApJ

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“…This is done both to minimize any systematic effects in the frequency measurements having to do with surface magnetism (e.g., Hindman et al 2000;Howe et al 2008) and to avoid the effects that strong localized magnetic fields may have on the flows themselves (e.g., Gizon et al 2001;Haber et al 2002;Hindman et al 2009;Featherstone 2011). In order to remove the well-known center-to-limb systematic bias (e.g., Zhao et al 2012;Greer et al 2013;Kholikov et al 2014;Jackiewicz et al 2015), we subtract the mean Doppler shift (as measured over the eleven analysis periods) from each wave mode at each disk position. This effectively removes both the center-to-limb systematic as well as the long-term global flow patterns associated with the rotation and meridional circulation.…”

Section: Measurement Of Horizontal Convective Flows Using Ring Analysismentioning

confidence: 99%

Helioseismic Imaging of Supergranulation Throughout the Sun’s Near-Surface Shear Layer

Greer

Hindman

Toomre

2016

ApJ

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We present measurements of the Sun's sub-surface convective flows and provide evidence that the pattern of supergranulation is driven at the surface. The pattern subsequently descends slowly throughout the near-surface shear layer in a manner that is inconsistent with a 3D cellular structure. The flow measurements are obtained through the application of a new helioseismic technique based on traditional ring analysis. We measure the flow field over the course of eleven days and perform a correlation analysis between all possible pairs of depths and temporal separations. In congruence with previous studies, we find that the supergranulation pattern remains coherent at the surface for slightly less than two days and the instantaneous surface pattern is imprinted to a depth of 7 Mm. However, these correlation times and depths are deceptive. When we admit a potential time lag in the correlation, we find that peak correlation in the convective flows descends at a rate of 10-40 m s −1 (or equivalently 1-3 Mm per day). Furthermore, the correlation extends throughout all depths of the near-surface shear layer. This pattern-propagation rate is well matched by estimates of the speed of downflows obtained through the anelastic approximation. Direct integration of the measured speed indicates that the supergranulation pattern that first appears at the surface eventually reaches the bottom of the near-surface shear layer a month later. Thus, the downflows have a Rossby radius of deformation equal to the depth of the shear layer and we suggest that this equality may not be coincidental.

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“…Contrary, direct numerical simulations, in most cases, predict the meridional circulation structure with multiple cells (see , Miesch & Hindman 2011;Gastine et al 2013;Guerrero et al 2013;Käpylä et al 2014;Featherstone & Miesch 2015;Hotta et al 2015). The double-cell (or multiple-cell) structure of the meridional circulation has been suggested by recent helioseismology inversions (Schad et al 2013;Zhao et al 2013;Kholikov et al 2014), but is still under debate. For example, Rajaguru & Antia (2015) found that the meridional circulation can be approximated by a single-cell structure with the return flow deeper than 0.77 R e .…”

Section: Introductionmentioning

confidence: 99%

On the Origin of the Double-cell Meridional Circulation in the Solar Convection Zone

Пипин

Kosovichev

2018

ApJ

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Recent advances in helioseismology, numerical simulations and mean-field theory of solar differential rotation have shown that the meridional circulation pattern may consist of two or more cells in each hemisphere of the convection zone. According to the mean-field theory the double-cell circulation pattern can result from the sign inversion of a nondiffusive part of the radial angular momentum transport (the so-called Λ-effect) in the lower part of the solar convection zone. Here, we show that this phenomenon can result from the radial inhomogeneity of the Coriolis number, which depends on the convective turnover time. We demonstrate that if this effect is taken into account then the solar-like differential rotation and the double-cell meridional circulation are both reproduced by the mean-field model. The model is consistent with the distribution of turbulent velocity correlations determined from observations by tracing motions of sunspots and large-scale magnetic fields, indicating that these tracers are rooted just below the shear layer.

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Meridional Flow in the Solar Convection Zone. I. Measurements From Gong Data

Cited by 50 publications

References 37 publications

A Comprehensive Method to Measure Solar Meridional Circulation and the Center-to-limb Effect Using Time–Distance Helioseismology

A Comprehensive Method to Measure Solar Meridional Circulation and the Center-to-limb Effect Using Time–Distance Helioseismology

Helioseismic Imaging of Supergranulation Throughout the Sun’s Near-Surface Shear Layer

On the Origin of the Double-cell Meridional Circulation in the Solar Convection Zone

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