A flux tube solar dynamo model based on the competing role of buoyancy and downflows

Abstract

A magnetic flux tube may be considered both as a separate body and as a confined field. As a field, it is affected both by differential rotation ($\Omega$-effect) and cyclonic convection ($\alpha$-effect). As a body, the tube experiences not only a buoyant force, but also a dynamic pressure due to downflows above the tube. These two competing dynamic effects are incorporated into the $\alpha$-$\Omega$ dynamo equations through the total magnetic turbulent diffusivity, leading to a flux tube dynamo operating in the convection zone. We analyze and solve the extended dynamo equations in the linear approximation by adopting the observed solar internal rotation and assuming a downflow effect derived from numerical simulations of solar convection zone. The model reproduces: the 22-year cycle period; the extended butterfly diagram with the confinement of strong activity to low heliographic latitudes $|\Phi|\le 35^\circ$; the evidence that at low latitudes the radial field is in an approximately $\pi$ phase lag compared to the toroidal field at the same latitude; the evidence that the poleward branch is in a $\pi/2$ phase lag with respect to the equatorward branch; and the evidence that most of the magnetic flux is present in an intermittent form, concentrated into strong flux tubes.