2017/08/17 by Gopal Hazra, Arnab Rai Choudhuri
Physics and Astronomy · #Astro and Planetary Science #Atmospheric sciences #Circulation (fluid dynamics) #Classical mechanics #Convection #Convection zone #Dynamo #Dynamo theory #Geophysics #Magnetic field #Mechanics #Meridional flow #Physics #Solar and Space Plasma Dynamics #Solar cycle #Solar dynamo #Solar maximum #Solar wind #Stellar, planetary, and galactic studies #Tachocline #Zonal and meridional #astro-ph.SR
paper · pdf · doi:10.1093/mnras/stx2152
15 pages, 11 figures, accepted for publication in MNRAS
arxiv created 2017/08/17 · openalex publication_date 2017/08/21 · arxiv updated 2017/10/11 · openalex created_date 2025/10/10 · openalex updated_date 2026/08/05
Observations of the meridional circulation of the Sun, which plays a key role in the operation of the solar dynamo, indicate that its speed varies with the solar cycle, becoming faster during the solar minima and slower during the solar maxima. To explain this variation of the meridional circulation with the solar cycle, we construct a theoretical model by coupling the equation of the meridional circulation (the ϕ component of the vorticity equation within the solar convection zone) with the equations of the flux transport dynamo model. We consider the back reaction due to the Lorentz force of the dynamo-generated magnetic fields and study the perturbations produced in the meridional circulation due to it. This enables us to model the variations of the meridional circulation without developing a full theory of the meridional circulation itself. We obtain results which reproduce the observational data of solar cycle variations of the meridional circulation reasonably well. We get the best results on assuming the turbulent viscosity acting on the velocity field to be comparable to the magnetic diffusivity (i.e. on assuming the magnetic Prandtl number to be close to unity). We have to assume an appropriate bottom boundary condition to ensure that the Lorentz force cannot drive a flow in the subadiabatic layers below the bottom of the tachocline. Our results are sensitive to this bottom boundary condition. We also suggest a hypothesis on how the observed inward flow towards the active regions may be produced.