TachoclineNear-surfaceshear layerPolar jet?Birch & Kosovichev (1998)Variations of differential rotation with timeMigrating zonal flows – “torsionaloscillations”Meridional flows from equator to polesVorontsov et al (2002)The depth structure of the torsional oscillations-migrate to the surface along the isorotation lines,-penetrate to the tachocline in high-latititude regionsVorontsov et al. 2002MDI dataModel extrapolationSolar cycle 24Howe et al (2006)

?
Howe et al, 2006Meridional flowsMigrating zonal flows – “torsionaloscillations”Meridional flows from equator to poles(Haber et al. !
2002)!2002200120001999199819971996The magnetic butterfly diagram. Axisymmetrical component of the line-of-sightmagnetic field averaged over a full solar rotation as a function of time. Yellowand blue colors shows positive and negative magnetic fieldsContours: toroidal fields at CZ baseGray-shades: surface radial fieldsObserved NSO map of longitude-averaged photospheric fields(Dikpati, de Toma, Gilman, Arge & White, 2004, ApJ, 601, 1136)Effect of the variationsof the meridional flowWhat is the shape of the tachocline, prolate?What is the high-latitude structure of the meridional circulation?

How deep is the meridional flow?View of the differential rotation from 60 degreesView of the zonal and meridional flows from 60 degreesWhat is the relationship between activelongitudes and polar magnetic field?
Yohkoh and EIT observations revealedgiants loop structure connecting activeregions and polar regions.
How deep is the link between plasma andflows in polar regions?YOKHOH observations of giant coronal loopsconnecting polar regions and following polaritiesof active regions. What is the role of theseconnections in the solar cycle?What is the large-scale circulation pattern in polar regionsand its role the magnetic field dynamics?What is the structure of supergranular convection and magnetic network at high latitudes?How well can we resolve structures andflows in the tachocline?A linear code solving wave propagationequations, including only spherical degreefrom 0 to 170.Surface focusingDeep focusingSound-speedperturbation of0.6% is placed at0.7R, with alatitudinaldependence, andwith a Gaussianshape. It’ssymmetric alongthe equator.

The simulation used here is 1024 minutes.Measured travel times are displayed after a reference profile issubtracted. The reference profile is measured from a simulationthat Thomas Hartlep made without perturbations.ModelInversion•The inversion recovers thelocation of the maximumperturbation well.

•The results are more spreadout, though, especiallytowards the deeper interior.
(may be related to relativelyhigh realization noise (shorttime series))•The latitudinal variation is notrecovered perfectly, but stillpromising.Averaging kernels obtained from surface-focusing inversions when the targetlocation is at a latitude of 18 degree, and at 0.7R, 0.8R, and 0.9R.• Structures are nothemisphere symmetric.
• Tachocline is clearlyseen, pretty muchlatitudinal dependent.
•(Zhao et al 2008,inpreparation)• Red and pink curves arefrom surface- and deepfocus, respectively.
• Tachocline is surprisinglyin good agreement!
• Should keep in mind theexperiments using simulateddata show that results are notwell localized.
•The next step is investigatevariations with the solarcycle. This requires carefulanalysis of MDI instrumentaleffects.Solar-C will open perspectives for stereo-helioseismology.
This will improve the tachocline resolution.MethodObservableInferencesRing-diagram analysis(Gough, Hill, November,Toomre, 1981)Local variations ofoscillation frequenciesLarge-scale soundspeed perturbations andhorizontal flowsTime-distancehelioseismology(Duvall et al. 1993)Acoustic Imaging(Chou, LaBonte, et al.
1990)Acoustic Holography(Lindsey & Braun, 1990)Phase and group traveltimes of acoustic andsurface gravity wavesPhase and amplitudevariationsPhase and amplitudevariations3D sound speed, densityand flows3D sound speed andflowsPhase variations andamplitude maps: noinversion procedure yetView of large-scale flows from Solar-CViews of the Sun from the SPI orbit and the Earth