Theory of Solar Meridional Circulation at High Latitudes
Abstract
We build a hydrodynamic model for computing and understanding the Sun's large-scale high-latitude flows, including Coriolis forces, turbulent diffusion of momentum, and gyroscopic pumping. Side boundaries of the spherical "polar cap," our computational domain, are located at latitudes >= 60°. Implementing observed low-latitude flows as side boundary conditions, we solve the flow equations for a Cartesian analog of the polar cap. The key parameter that determines whether there are nodes in the high-latitude meridional flow is epsilon = 2ΩnπH 2/ν, where Ω is the interior rotation rate, n is the radial wavenumber of the meridional flow, H is the depth of the convection zone, and ν is the turbulent viscosity. The smaller the epsilon (larger turbulent viscosity), the fewer the number of nodes in high latitudes. For all latitudes within the polar cap, we find three nodes for ν = 1012 cm2 s-1, two for 1013, and one or none for 1015 or higher. For ν near 1014 our model exhibits "node merging": as the meridional flow speed is increased, two nodes cancel each other, leaving no nodes. On the other hand, for fixed flow speed at the boundary, as ν is increased the poleward-most node migrates to the pole and disappears, ultimately for high enough ν leaving no nodes. These results suggest that primary poleward surface meridional flow can extend from 60° to the pole either by node merging or by node migration and disappearance.
- Publication:
-
The Astrophysical Journal
- Pub Date:
- February 2012
- DOI:
- 10.1088/0004-637X/746/1/65
- arXiv:
- arXiv:1112.1107
- Bibcode:
- 2012ApJ...746...65D
- Keywords:
-
- hydrodynamics;
- Sun: dynamo;
- Sun: interior;
- Sun: photosphere;
- Sun: rotation;
- Astrophysics - Solar and Stellar Astrophysics
- E-Print:
- Accepted in ApJ