Gyroscopic Pumping in the Solar Near-Surface Shear Layer

Abstract

We use global and local helioseismic inversions to explore the prevailing dynamical balances in the solar Near-Surface Shear Layer (NSSL). The differential rotation and meridional circulation are intimately linked, with a common origin in the turbulent stresses of the upper solar convection zone. The existence and structure of the NSSL cannot be attributed to the conservation of angular momentum by solar surface convection, as is often supposed. Rather, the turbulent angular momentum transport accounts for the poleward meridional flow while the often overlooked meridional force balance maintains the mid-latitude rotational shear. We suggest that the base of the NSSL is marked by a transition from baroclinic to turbulent stresses in the meridional plane which suppress Coriolis-induced circulations that would otherwise establish a cylindrical rotation profile. The turbulent angular momentum transport must be non-diffusive and directed radially inward. Inferred mean flows are consistent with the idea that turbulent convection tends to mix angular momentum but only if the mixing efficiency is inhomogeneous and/or anisotropic. The latitudinal and longitudinal components of the estimated turbulent transport are comparable in amplitude and about an order of magnitude larger than the vertical component. We estimate that it requires 2--4% of the solar luminosity to maintain the solar NSSL against the inertia of the mean flow. Most of this energy is associated with the turbulent transport of angular momentum out of the layer, with a spin-down time scale of $\sim$ 600 days. We also address implications of these results for numerical modeling of the NSSL.

26 pages, 11 Figures, Accepted on August 25, 2011 for publication in the Astrophysical Journal

References in corpus (7)

• Solar differential rotation and meridional flow: The role of a subadiabatic tachocline for the Taylor-Proudman balance
• Structure and Evolution of Giant Cells in Global Models of Solar Convection
• Solar Meridional Circulation from Doppler Shifts of the Fe I line at lambda 5250 Angstroms as Measured by the 150-foot Solar Tower Telescope at the Mt. Wilson Observatory
• On the penetration of meridional circulation below the solar convection zone
• Origin of solar torsional oscillations
• Latitudinal variation of the solar photospheric intensity
• Modeling the Near-Surface Shear Layer: Diffusion Schemes Studied With CSS

Cited by in corpus (53)

• From solar-like to anti-solar differential rotation in cool stars
• Meridional Circulation in Solar and Stellar Convection Zones
• On differential rotation and overshooting in solar-like stars
• Differential rotation in solar-like stars from global simulations
• Grand Minima and Equatorward Propagation in a Cycling Stellar Convective Dynamo
• Zonal flow regimes in rotating anelastic spherical shells: an application to giant planets
• Magnetically controlled stellar differential rotation near the transition from solar to anti-solar profiles
• High-resolution calculation of the solar global convection with the reduced speed of sound technique: II. Near surface shear layer with the rotation
• On the role of tachoclines in solar and stellar dynamos
• Confirmation of bistable stellar differential rotation profiles
• The Spectral Amplitude of Stellar Convection and its Scaling in the High-Rayleigh-Number Regime
• The Solar-Stellar Connection
• Meridional Flow in the Solar Convection Zone II: Helioseismic Inversions of GONG Data
• On the Amplitude of Convective Velocities in the Deep Solar Interior
• The Wisconsin Plasma Astrophysics Laboratory
• Surface flux evolution constraints for flux transport dynamos
• Generation solar-like differential rotation
• Global model of differential rotation in the Sun
• Mean field models of flux transport dynamo and meridional circulation in the Sun and stars
• Differential rotation of main-sequence dwarfs: predicting the dependence on surface temperature and rotation rate
• Evidence for multiple Ferrel-like cells on Jupiter
• Theory of solar oscillations in the inertial frequency range: Linear modes of the convection zone
• Understanding solar torsional oscillations from global dynamo models
• Differential rotation in main-sequence solar-like stars: Qualitative inference from asteroseismic data
• The Role of Downflows in Establishing Solar Near-Surface Shear
• Meridional circulation dynamics from 3D MHD global simulations of solar convection
• Driving Solar Giant Cells through the Self-Organization of Near-Surface Plumes
• Theory of differential rotation and meridional circulation
• Leptocline as a Shallow Substructure of Near-Surface Shear Layer in 3D Radiative Hydrodynamic Simulations
• Solar Dynamics, Rotation, Convection and Overshoot
• Exploring cycle period and parity of stellar magnetic activity with dynamo modeling
• The Sun's differential rotation is controlled by high-latitude baroclinically unstable inertial modes
• Double-Cell Type Solar Meridional Circulation Based on Mean-Field Hydrodynamic Model
• Solar-like to Antisolar Differential Rotation: A Geometric Interpretation
• Meridional Circulation Dynamics in a Cyclic Convective Dynamo
• On the origin of the double cell meridional circulation in the solar convection zone
• On the dynamics of overshooting convection in spherical shells: Effect of density stratification and rotation
• Magnetic and rotational quenching of the $\Lambda$ effect
• The Quest to Understand Supergranulation and Large-Scale Convection in the Sun
• Convection in Oblate Solar-Type Stars
• Implicit large eddy simulations of global solar convection: effects of numerical resolution in non-rotating and rotating cases
• Angular momentum fluxes caused by Lambda-effect and meridional circulation structure of the Sun
• Solar differential rotation: hints to reproduce a near-surface shear layer in global simulations
• Global Turbulent Solar Convection: a Numerical Path Investigating Key Force Balances in the context of the Convective Conundrum
• A Poynting-Robertson-like drag at the Sun's surface
• Investigation of the dependence of angular momentum transport on spatial scales for construction of differential rotation
• Assessing the Observability of Deep Meridional Flow Cells in the Solar Interior
• Seismology of the Sun : Inference of Thermal, Dynamic and Magnetic Field Structures of the Interior
• Simulating the outer layers of rapidly rotating stars
• Global simulations of stellar dynamos
• Generation of mean flows in rotating anisotropic turbulence: The case of solar near-surface shear layer
• Confinement of the Solar Tachocline by Dynamo Action in the Radiative Interior
• Evolution and characteristics of forced shear flows in polytropic atmospheres: Large and small Péclet number regimes