A New Component of Solar Dynamics: North-South Diverging Flows Migrating toward the Equator with an 11 Year Period

Beck, J. G.; Gizon, Laurent; Duvall, T. L.

doi:10.1086/342636

Cited by 75 publications

(62 citation statements)

References 16 publications

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“…The residual flows shown here agree with f-mode analysis near the photosphere (Gizon 2003), and are in general agreement with findings from the ring-diagram analyses (Haber et al 2002;Basu & Antia 2003) that the gradient of the near-equator meridional flows steepen with the development of the solar cycle toward the solar maximum. However, divergent meridional flows from activity belts are found in much deeper solar layers in other timedistance studies (Chou & Dai 2001;Beck et al 2002).…”

Section: Meridional Flowmentioning

confidence: 71%

“…By performing time-distance measurements, Chou & Dai (2001) and Beck et al (2002) detected migrating outflows from the solar activity belts, in addition to the normal poleward meridional flows. However, from the measurement of acoustic travel times alone, without doing inversions, it is difficult to determine the depth of the divergent flows.…”

Section: Discussionmentioning

confidence: 99%

“…Although an acousticwave theory for time-distance helioseismology is under development (Birch & Kosovichev 2000;, it was argued that ray approximation could give credible inversion results with fewer computations (Birch et al 2001;Jensen et al 2001). Because of a cross-talk effect between the horizontal divergence and the vertical flows in time-distance measurement (Kosovichev & Duvall 1997), the weak vertical flows in the quiet solar regions derived from our inversions are considered less reliable than the stronger vertical velocity in active regions (Zhao & Kosovichev 2003).…”

Section: Data Reductionmentioning

confidence: 99%

“…More recent studies show that the meridional flows also vary with the solar cycle. Measurements of acoustic travel times (Chou & Dai 2001;Beck, Gizon, & Duvall 2002) imply that, after subtracting a smooth poleward meridionalflow profile, the residual meridional flow shows divergent flow patterns around the solar activity belts below a depth of 18 Mm or so. This divergent flow pattern migrates toward the solar equator together with the activity belts.…”

Section: Introductionmentioning

confidence: 99%

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Torsional Oscillation, Meridional Flows, and Vorticity Inferred in the Upper Convection Zone of the Sun by Time‐Distance Helioseismology

Zhao

Kosovichev

2004

ApJ

314

241

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By applying time-distance helioseismology measurements and inversions to Solar and Heliospheric Observatory (SOHO) Michelson Doppler Imager (MDI) dynamics campaign data, we obtain synoptic maps of subsurface plasma-flow fields at a depth of 0-12 Mm for seven solar Carrington rotations, covering the years 1996-2002, from solar-activity minimum to maximum. Vorticity distribution and both zonal and meridional flows are derived from such synoptic flow maps, which contain an enormous amount of information about solar dynamics. The results for the zonal flows agree well with previous results. The meridional flows of an order of 20 m s À1 are found to remain poleward during the whole period of observations. In addition to the poleward meridional flows observed at the solar minimum, extra meridional circulation cells of flow converging toward the activity belts are found in both hemispheres, which may imply plasma downdrafts in the activity belts. These converging flow cells migrate toward the solar equator together with the activity belts as the solar cycle evolves. The vorticity distributions are largely linear with latitude, and the deviations from the vorticity caused by the mean differential rotation are presented. Patterns of large-scale flows are investigated for a large active region at different depths. Converging flows toward the center of the active region are found near the solar surface, and divergent flows in this large active region are found to be rooted much deeper than similar flows observed in individual sunspots. We conclude that the extremely rich and complicated dynamics of the upper convection zone reveal remarkable organization on the large scale, which can be correlated with the magnetic activity zones.

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Section: Meridional Flowmentioning

confidence: 71%

Section: Discussionmentioning

confidence: 99%

Section: Data Reductionmentioning

confidence: 99%

Section: Introductionmentioning

confidence: 99%

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Torsional Oscillation, Meridional Flows, and Vorticity Inferred in the Upper Convection Zone of the Sun by Time‐Distance Helioseismology

Zhao

Kosovichev

2004

ApJ

314

241

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“…This represents a significant improvement in latitude coverage over helioseismic measurements of the meridional flow (see, e.g., Haber et al 2002 andBeck, Gizon, &Duvall 2002 for some recent results). Unlike Figure 5, some of the helioseismic measurements have shown evidence of a second cell in latitude.…”

Section: Discussionmentioning

confidence: 90%

Wavelike Properties of Solar Supergranulation Detected in Doppler Shift Data

Schou

2003

ApJ

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Recently, Gizon, Duvall, & Schou suggested that supergranulation has a wavelike component. In this Letter, I show that the same phenomenon can be observed using surface Doppler shift data, thereby confirming their observations, which were made using a helioseismic time-distance technique. In addition to confirming those results, I show that the wave motion is predominantly longitudinal (the fluid displacement is in the direction of propagation), and I am able to extend the results for the rotation and the meridional flow beyond ‫07ע‬Њ latitude. The meridional flow results, which extend further than previous helioseismic measurements, appear to show no sign of a second cell.

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Measuring helioseismic travel times

2007

Self Cite

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In time-distance helioseismology wave travel times are measured from the cross-correlation between Doppler velocities recorded at any two locations on the solar surface. We compare two different methods to extract the travel times from the noisy cross-correlation functions. The first method consists of fitting a 5-parameter analytic function to the crosscorrelation to obtain the phase travel time. The second method consists of linearizing the distance between the observed cross-correlation and a sliding reference cross-correlation (the only parameter is the travel time). We find that the oneparameter fits are more robust with respect to noise. Using SOHO data from the MDI Structure Program for the years 1996-2003, we study in detail the statistical properties of the noise associated with the travel-time measurements for the two different fitting methods.

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A New Component of Solar Dynamics: North-South Diverging Flows Migrating toward the Equator with an 11 Year Period

Cited by 75 publications

References 16 publications

Torsional Oscillation, Meridional Flows, and Vorticity Inferred in the Upper Convection Zone of the Sun by Time‐Distance Helioseismology

Torsional Oscillation, Meridional Flows, and Vorticity Inferred in the Upper Convection Zone of the Sun by Time‐Distance Helioseismology

Wavelike Properties of Solar Supergranulation Detected in Doppler Shift Data

Measuring helioseismic travel times

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