Solar sunspot cycle and the butterfly diagram

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

Schematic flux-transport dynamo model1. Shearing of poloidal fieldsby differential rotation toproduce new toroidal fields,followed by eruption ofsunspots.

2. Spot-decay and spreadingto produce new surfaceglobal poloidal fields.

3.Transport of poloidal fields bymeridional circulation (conveyorbelt) toward the pole and downto the bottom, followed byregeneration of new toroidalfields of opposite sign.
Dikpati et al 2006

Contours: toroidal fields at CZ baseGray-shades: surface radial fields(Dikpati, de Toma, Gilman, Arge & White, 2004, ApJ, 601, 1136)

Effect of the variablemeridional flowGeomagnetic aa index at the solar minimum isthe best known indicator of the strength of thefollowing solar cycle (Ohl, 1966)

Hathaway, Wilson, Reichmann (1999)

Why? Because high-speed solar wind duringthe activity minima comes mostly from thepolar regions.

Prediction of Solar cycle 24 by dataassimilation method

Kitiashvili & Kosovichev (2008)

Key targets and helioseismologymeasurements1.
2.
3.
4.
5.
6.
7.

Torsional oscillationsMeridional flowFlux transport (supergranular diffusion)Complexes of activityFlux emergencePolarity reversalsMagnetic and kinetic helicity

Variations of the differential rotationwith time called “torsional oscillations”Migrating zonal flows – “torsionaloscillations”

Meridional flows from the equator to poles

Solar cycle 24

Howe et al (2006)

Strongest variations of the differential rotationare observed in high-latitude regions

Vorontsov et al (2002)

(Haber et al. !
2002)!

2002

2001

2000

1999

1998

1997

1996

Zhao & Kosovichev (2004)

Perhaps, solar dynamo is notlocated in the tachocline? –Paradigm shiftHowe et al, 2006

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?

High-Resolution Subsurface Flow Fieldsinside the Sunspot

Comparing MDI and Hinode SunspotSubsurface StructureMDI AR8243

Hinode AR10953

Note that the two studies are for two different active regions, andthe sizes of sunspots are also different. However, the negative andpositive sound speed perturbation structures look similar, and theconversion depth is similar.

Hinode Observations of Solar South PoleArea

The observation was taken on March 15,2008, when the solar south pole was pointingous with a B-angle of -7.17 . The duration ofobservation was approximately 13 hours. Weused the first 8.5 hours for this analysis.

A Closer Look at the Observation

The observation was made using Ca II H line, which has been demonstratedsuitable for local helioseismology analysis (Sekii, Kosovichev, Zhao et al.
2007, PASJ). The FOV covers -65o to -82o or so in latitude.

Supergranular Structures Seen from TimeDistance Travel Time MeasurementThe measured acoustictravel time map using thetime-distancehelioseismology techniqueshows supergranularstructures in this highlatitude area. Thesestructures are weaker inlatitude higher than 75oNagashima,Zhao, Kosovichev, Sekii (2009)

Outward – inward travel time difference mapswith different annulus sizes	

Δ=8Mm	
  Δ=14	
  Mm	
  Δ=21	
  Mm	
  max	
  depth	  D=	  2Mm	  	 max	
  depth	  D=	  4.5Mm	
  	 max	
  depth	  D=	  8Mm	Δ	

 The alignment is seen

down to ~5Mm depth.	
Nagashima, PhD thesis (2010)D	31	
  Combining MDI and Hinode Results

The Hinode results look consistent with the MDI results. Still, there is a datagap between results. We are working to fill up this gap.

Surface focusing

Deep focusing

Measured travel times are displayed after a reference profile issubtracted. The reference profile is measured from a simulationthat Thomas Hartlep made without perturbations.

Inversion result using 18-hoursArtificial sound-speed profileof simulated oscillation signal

Inversion of 1-month ofMDI data

MDI instrumental distortions may corrupt the results.
MDI was not designed for this type of measurements.

Solar-C will answer the basic science questionscritical for understanding the solar dynamo andsunspot cycles

 What is the role of polar magnetism in the solar dynamo andcycle?
 What is the mechanism of the polar field reversals?
 How does the high-latitude field of the Sun evolve on arange of scales?
 What are the properties of the Sun's surface and subsurfacemeridional flow and differential rotation at high latitude, andhow do these vary with time and position?
 How do the average properties of granular andsupergranular flows depend on latitude?
 What are the properties of emerging flux at high latitudes?
 How is field removed from the solar surface around the highlatitude polarity inversion regions?
 What are the signatures of the solar dynamo action near thebottom of the convective envelope?

Relationship to Solar Orbiter andSDO Solar Orbiter will provide important support for

the Solar-C mission by doing different out-ofecliptic observations. It will reach 35 degreeslatitudes after ~10 years after launch, in2026-2028.
 SDO will provide uninterrupted observations ofmagnetic field and Doppler shift, and will coverthe whole Sun except the polar regions. SDOwas designed to “solve” the dynamo problem,but the Hinode discovery of the strong polarfields shows that the SDO alone will beinsufficient.

… but Hinode discovered that the polar magnetic field isextremely structured, and HMI will not be able to resolve thestructure and dynamics of the polar fields at this scale.

Schematic flux-transport dynamo model

1. Shearing of poloidal fieldsby differential rotation toproduce new toroidal fields,followed by eruption ofsunspots.
2. Spot-decay and spreadingto produce new surfaceglobal poloidal fields.

3. Transport of poloidal fields bymeridional circulation (conveyorbelt) toward the pole and downto the bottom, followed byregeneration of new toroidalfields of opposite sign.
Dikpati et al 2006

 The internal structure and dynamics of the near

polar regions of the Sun are a key to ourunderstanding of the solar dynamo and predictingof the solar activity cycles.
 Solar-C will provide a unique opportunity todirectly observe and analyze magnetic fields, thedifferential rotation, supergranulation andmeridional flows at high latitudes and near thesolar poles.
 Synergy with a high-resolution helioseismologymission in the ecliptic plane or a ground-basenetwork is critical.

Views of the Sun from the SPI orbit and the Earth