Solar-Cycle Variation of Subsurface Meridional Flow Derived with Ring-Diagram Analysis

Komm, R.; Hernández, I. Gonzälez; Howe, R.; Hill, F.

doi:10.1007/s11207-015-0729-5

Cited by 44 publications

(39 citation statements)

References 45 publications

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“…Notice that the radial dependence of the stream function is raised to (r − r mc ) 2.5 , compared with (r − r mc ) 2 in Jouve et al (2008) and Paper I. This can give a higher ratio of maximum flow v θ at the surface with respect to that of the base of the convection zone, which in turn results in a 22-year magnetic cycle dynamo model with a surface flow ∼ 20 ms −1 (Yeates et al 2008), consistent with the observed solar surface flow (Ulrich 2010;Basu & Antia 2010;Komm et al 2015). The expansion coefficients d k,l (t) are modulated in time so that the flow is time dependent.…”

Section: Appendix the Babcock-leighton Flux Transport Mean Field Dynasupporting

confidence: 65%

“…In particular, we present the surface flow in Fig. 4 (a), and note again that similar time variability is also reported in the Sun (eg., Ulrich & Boyden 2005;Komm et al 2015). The plots show the asymmetry of the flow about the equator.…”

Section: Methodsmentioning

confidence: 99%

“…Again, this study assumed a steady meridional circulation. In reality, the solar cycle is significantly modulated, and the meridional flow is fluctuating (Ulrich 2010;Basu & Antia 2010;Komm et al 2015), (for more about observations of meridional flow, see Haber et al 2002aHaber et al , 2003Zhao et al 2004Zhao et al , 2012Zhao et al , 2013aŠvanda et al 2007Schad et al 2013;Upton & Hathaway 2014), so the next step of development is to verify the applicability of the method to capture the variability of the modulated activity.…”

Section: Solar Prediction and Data Assimilation Methodsmentioning

confidence: 99%

See 2 more Smart Citations

Variational Estimation of the Large-scale Time-dependent Meridional Circulation in the Sun: Proofs of Concept with a Solar Mean Field Dynamo Model

Hung

Brun

Fournier

et al. 2017

ApJ

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We present in this work the development of a solar data assimilation method based on an axisymmetric mean field dynamo model and magnetic surface data, our mid-term goal is to predict the solar quasi cyclic activity. Here we focus on the ability of our algorithm to constrain the deep meridional circulation of the Sun based on solar magnetic observations. To that end, we develop a variational data assimilation technique. Within a given assimilation window, the assimilation procedure minimizes the differences between data and the forecast from the model, by finding an optimal meridional circulation in the convection zone, and an optimal initial magnetic field, via a quasi-Newton algorithm. We demonstrate the capability of the technique to estimate the meridional flow by a closed-loop experiment involving 40 years of synthetic, solar-like data. By assimilating the synthetic magnetic proxies annually, we are able to reconstruct a (stochastic) time-varying meridional circulation which is also slightly equatorially asymmetric. We show that the method is robust in estimating a flow whose level of fluctuation can reach 30% about the average, and that the horizon of predictive capability of the method is of the order of 1 cycle length.

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Section: Appendix the Babcock-leighton Flux Transport Mean Field Dynasupporting

confidence: 65%

Section: Methodsmentioning

confidence: 99%

Section: Solar Prediction and Data Assimilation Methodsmentioning

confidence: 99%

See 1 more Smart Citation

Variational Estimation of the Large-scale Time-dependent Meridional Circulation in the Sun: Proofs of Concept with a Solar Mean Field Dynamo Model

Hung

Brun

Fournier

et al. 2017

ApJ

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“…For cycle 24, the polar branch is significantly weaker than it was in the previous cycles (Zhao et al 2014;Komm et al 2014;Kosovichev & Zhao 2016). Additionally, recent helioseismology observations showed that the TO correlate with the variations of the meridional flows (Zhao et al 2014;Komm et al 2015). The evident dependence of the TO on the solar activity cycle provides a unique opportunity to explore the interaction between large-scale magnetic field and flows.…”

Section: Introductionmentioning

confidence: 92%

Understanding Solar Torsional Oscillations From Global Dynamo Models

Gómez

Smolarkiewicz

Pino

et al. 2016

ApJL

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The phenomenon of solar "torsional oscillations" (TO) represents migratory zonal flows associated with the solar cycle. These flows are observed on the solar surface and, according to helioseismology, extend through the convection zone. We study the origin of the TO using results from a global MHD simulation of -2 -the solar interior that reproduces several of the observed characteristics of the mean-flows and magnetic fields. Our results indicate that the magnetic tension (MT) in the tachocline region is a key factor for the periodic changes in the angular momentum transport that causes the TO. The torque induced by the MT at the base of the convection zone is positive at the poles and negative at the equator. A rising MT torque at higher latitudes causes the poles to speed-up, whereas a declining negative MT torque at the lower latitudes causes the equator to slow-down. These changes in the zonal flows propagate through the convection zone up to the surface. Additionally, our results suggest that it is the magnetic field at the tachocline that modulates the amplitude of the surface meridional flow rather than the opposite as assumed by flux-transport dynamo models of the solar cycle.

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“…Furthermore, Komm et al (2015) showed that the inflows are part of the extended solar cycle, beginning at mid-latitudes (about 40 degrees). The inflows then propagate equatorward together with the activity belts.…”

Section: Inflows Maintaining the Activity Beltsmentioning

confidence: 99%

The turbulent diffusion of toroidal magnetic flux as inferred from properties of the sunspot butterfly diagram

Cameron

Schüßler

2016

A&A

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Context. In order to match observed properties of the solar cycle, flux-transport dynamo models require the toroidal magnetic flux to be stored in a region of low magnetic diffusivity, typically located at or below the bottom of the convection zone. Aims. We infer the turbulent magnetic diffusivity affecting the toroidal field on the basis of empirical data. Methods. We considered the time evolution of mean latitude and width of the activity belts of solar cycles 12-23 and their dependence on cycle strength. We interpreted the decline phase of the cycles as a diffusion process. Results. The activity level of a given cycle begins to decline when the centers of its equatorward propagating activity belts come within their (full) width (at half maximum) from the equator. This happens earlier for stronger cycles because their activity belts are wider. From that moment on, the activity and the belt width decrease in the same manner for all cycles, independent of their maximum activity level. In terms of diffusive cancellation of opposite-polarity toroidal flux across the equator, we infer the turbulent diffusivity experienced by the toroidal field, wherever it is located, to be in the range 150-450 km 2 s −1 . Strong diffusive latitudinal spreading of the toroidal flux underneath the activity belts can be inhibited by an inflow toward the toroidal field bands in the convection zone with a magnitude of several meters per second. Conclusions. The inferred value of the turbulent magnetic diffusivity affecting the toroidal field agrees, to order of magnitude, with estimates based on mixing-length models for the solar convection zone. This is at variance with the requirement of flux-transport dynamo models. The inflows required to keep the toroidal field bands together before they approach the equator are similar to the inflows toward the activity belts observed with local helioseismology.

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Solar-Cycle Variation of Subsurface Meridional Flow Derived with Ring-Diagram Analysis

Cited by 44 publications

References 45 publications

Variational Estimation of the Large-scale Time-dependent Meridional Circulation in the Sun: Proofs of Concept with a Solar Mean Field Dynamo Model

Variational Estimation of the Large-scale Time-dependent Meridional Circulation in the Sun: Proofs of Concept with a Solar Mean Field Dynamo Model

Understanding Solar Torsional Oscillations From Global Dynamo Models

The turbulent diffusion of toroidal magnetic flux as inferred from properties of the sunspot butterfly diagram

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