Presentation on theme: "1 The Sun as a whole: Rotation, Meridional circulation, and Convection Michael Thompson High Altitude Observatory, National Center for Atmospheric Research."— Presentation transcript:
1 The Sun as a whole: Rotation, Meridional circulation, and Convection Michael Thompson High Altitude Observatory, National Center for Atmospheric Research Boulder, Colorado, USA
Rotation of the Sun – the stellar context Light-curve of star CoRoT-2 (courtesy of T. Reinhold) Kepler: Rotation of 16 Cyg Davis et al McQuillan et al. (2014) have used Kepler to measure rotation periods for 34,030 stars Skumanich 1972
Rotation of the Sun – from helioseismology Gradient of rotation in near-surface shear layer Barekat et al. 2014, submitted Inferred internal rotation profile. Note shear layers at base of convection zone (shaded white) and in near-surface.
Rotation of the Sun – modeling Mean flow regimes in spherical convection (Featherstone & Miesch 2014) Rapidly-rotating regimeSlowly-rotating regime Solar rotationAnti-solar rotation
Rotation of the Sun – temporal variations Courtesy of R. Howe
Meridional circulation – possible role in solar dynamo N-Pole S-Pole Red: α -effect location Green: rotation contours Blue: meridional flow Courtesy of M. Dikpati Meridional circulation plays a key role in the flux- transport dynamo model. It carries decayed AR flux from the surface down into the tachocline region, and it sets the clock for the 11- year solar cycle.
Meridional circulation – from helioseismology Meridional flow in near-surface layers Courtesy of D. Haber Meridional flow – multi-cell structure Zhao et al Meridional flow from global mode coupling Schad et al. 2013
Mean flow regimes in spherical convection (Featherstone & Miesch 2014) Rapidly-rotating regimeSlowly-rotating regime Solar rotationAnti-solar rotation Meridional circulation – modeling
Convection – on diverse scales Granulation: ~ 1 Mm Supergranulation: ~ Mm Giant cells? ~ Mm Astronomy Picture of the Day 2005 November 6
Convection – from helioseismology Inferred convective flows at 0.3Mm depth from helioseismology Courtesy of B. Greer
Convection – supergranules and moat flows Mean supergranular flows. Radial (left) and tangential (right) flow speeds. Courtesy J. Langfellner Comparing mean moat (top row) and super- granular (bottom row) flows. Radial (left) and vertical (right) flows. Svanda et al. 2014
Convection – modeling Magnetoconvection simulations in 24x24x6Mm box by M. Schuessler: mean vertical field 100G (top) and 400G (bottom) – Hanasoge et al Radial velocity at 0.98R (top) and 0.95R (bottom) in spherical “ASH” simulation: whole-sun projection – Miesch et al. 2008
Convection – a puzzle The solar convection operates at much lower flow speeds in the bulk of the convection zone than models suggest, according to helioseismic travel-time measurements. Hanasoge et al. 2012
Summary Rotation Precision photometry and asteroseismology are now putting Sun in context of other stars. Helioseismology reveals dynamically important shear layers. An evolving picture of torsional oscillations. Simulations suggestion Sun is delicately poised between solar and anti- solar differential rotation regimes. Meridional circulation Helioseismology suggests a shallow return flow and multi-cell structure in depth. But result depends on as-yet uncertain center-to-limb correction of travel times. Simulations suggest Sun is delicately poised between single-cell and multi- cell regimes. Convection Ensemble averaging reveals mean supergranular and sunspot moat flows. Major puzzle over strength of convective velocities … appear to be too strong in spherical simulations. Suggests a possible role for unresolved down-plumes in solar convection.