Helioseismic Measurements of the Subsurface Meridional Flow

Braun, D. C.; Fan, Yuhong

doi:10.1086/311727

Cited by 121 publications

(122 citation statements)

References 22 publications

Supporting

Mentioning

110

Contrasting

Order By: Relevance

“…The result by Hathaway et al (2003) shows that the drift rate from the center of the butterfly diagram is anti correlated with the cycle length, so that the faster the drift of the butterfly diagram is, the shorter are the cycles. On the other hand, the helioseismic findings of Braun and Fan (1998) support a surface poleward flow of order 10 m/s, while the results of Zhao and Kosovichev (2004) detect a flow which is always poleward. The helioseismic approach can basically trace the presence of the meridional flow up to a depth of few (less Corresponding author: abo@ct.astro.it than 15) Mm, the UV bright points are in principle a different diagnostic.…”

Section: Introductionmentioning

confidence: 81%

Advection‐dominated solar dynamo model with two‐cell meridional flow and a positive α ‐effect in the tachocline

Bonanno¹,

Elstner

Belvedère

2006

Astron Nachr

View full text Add to dashboard Cite

Most probably the sunspot cycle period is ruled by a meridional flow located near the base of the convection zone (Hathaway et al. 2003). On the other hand, if the eddy diffusivity is low enough, dramatic modification of the standard α 2 Ω-dynamo by the meridional flow are expected. In this paper we shall discuss the dependence of periods, dynamo numbers and the sign of the current helicity as a function of the magnetic Reynolds number for a double cell meridional circulation and for a positive α-effect at the base of the convection zone. The dynamo action occurs at lower latitudes and its location is at the interface between equatorward and poleward motions near the base of the convection zone. In spite of the complexity of the flow pattern, our simulations show that the resulting dynamo action reproduces several observed features of the solar cycle.

show abstract

Section: Introductionmentioning

confidence: 81%

Advection‐dominated solar dynamo model with two‐cell meridional flow and a positive α ‐effect in the tachocline

Bonanno¹,

Elstner

Belvedère

2006

Astron Nachr

View full text Add to dashboard Cite

show abstract

“…Confidence in local helioseismic methods is also obtained by comparing models of low-amplitude flows such as meridional circulation derived using different procedures and assumptions (e.g., Giles et al 1997Giles et al , 1998Braun & Fan 1998;Haber et al 2002;Hughes & Thompson 2003;Zhao & Kosovichev 2004;Chou & Ladenkov 2005;González Hernández et al 2006;Š vanda et al 2007). Intercomparisons of methods and data sets can sometimes lead to the discovery of important systematic effects or artifacts (González Hernández et al 2006).…”

Section: Introductionmentioning

confidence: 99%

Helioseismic Holography of Simulated Solar Convection and Prospects for the Detection of Small‐Scale Subsurface Flows

Braun

Birch

Benson

et al. 2007

ApJ

Self Cite

View full text Add to dashboard Cite

We perform helioseismic holography on realistic solar convection simulations and compare the observed traveltime perturbations with the expected travel times from the horizontal flows in the simulations computed from forward models under the assumption of the Born approximation. We demonstrate reasonable agreement between the observed and model travel times, which reinforces the validity of helioseismic holography in the detection of subsurface horizontal flows. An assessment is made of the uncertainty of the measured p-mode travel times from the rms of the residuals. From the variation of the signal-to-noise ratio with depth we conclude that the helioseismic detection of individual flow structures with spatial scales of supergranulation or smaller is not possible for depths below about 5 Mm below the surface over timescales of less than a day. The travel-time noise estimated from these simulations appears to be similar to noise in measurements made using solar observations. We therefore suggest that similar limitations exist regarding the detection of analogous subsurface flows in the Sun. A study of the depth dependence of the contribution to the travel-time perturbations for focus depths between 3 and 7 Mm is made, showing that approximately half of the observed signal originates within the first 2 Mm below the surface. A consequence of this is a rapid decrease (and reversal in some cases) of the travel-time perturbations with depth due to the contribution to the measurements of oppositely directed surface flows in neighboring convective cells. This confirms an earlier interpretation of similar effects reported from observations of supergranulation. Subject headingg s: Sun: helioseismology -Sun: interior

show abstract

“…A meridional flow toward the pole is observed in the outer half of the SCZ (Hathaway 1996;Braun & Fan 1998) and had been used earlier to model the evolution of the weak diffuse poloidal field on the surface (Wang et al 1991;Dikpati & Choudhuri 1994). Fluctuations in the meridional flow (Hathaway 1996), believed to be a product of turbulent convection, have also successfully accounted for variations in the solar cycle that are superposed on the otherwise stable 11 yr periodicity (Charbonneau & Dikpati 2000;Wang et al 2002).…”

Section: Introductionmentioning

confidence: 99%

Evidence That a Deep Meridional Flow Sets the Sunspot Cycle Period

Hathaway

Nandy

Wilson

et al. 2003

ApJ

149

119

View full text Add to dashboard Cite

Sunspots appear on the Sun in two bands on either side of the equator that drift toward lower latitudes as each sunspot cycle progresses. We examine the drift of the centroid of the sunspot area toward the equator in each hemisphere from 1874 to 2002 and find that the drift rate slows as the centroid approaches the equator. We compare the drift rate at sunspot cycle maximum with the period of each cycle for each hemisphere and find a highly significant anticorrelation: hemispheres with faster drift rates have shorter periods. These observations are consistent with a meridional counterflow deep within the Sun as the primary driver of the migration toward the equator and the period associated with the sunspot cycle. We also find that the drift rate at maximum is significantly correlated with the amplitude of the following cycle, a prediction of dynamo models that employ a deep meridional flow toward the equator. Our results indicate an amplitude of about 1.2 m s À1 for the meridional flow velocity at the base of the solar convection zone.

show abstract

Helioseismic Measurements of the Subsurface Meridional Flow

Cited by 121 publications

References 22 publications

Advection‐dominated solar dynamo model with two‐cell meridional flow and a positive α ‐effect in the tachocline

Advection‐dominated solar dynamo model with two‐cell meridional flow and a positive α ‐effect in the tachocline

Helioseismic Holography of Simulated Solar Convection and Prospects for the Detection of Small‐Scale Subsurface Flows

Evidence That a Deep Meridional Flow Sets the Sunspot Cycle Period

Contact Info

Product

Resources

About