Small scale alpha-squared effect in the solar convection zone

Abstract

Phenomena of self-organization of macroscopic structures in nature caused by the negative turbulent viscosity, which is basically the transfer of energy of the turbulent helical motion from small to large eddies (so-called inverse energy cascade), are reviewed. The effect of the helical negative turbulent diffusion (small-scale α2 effect by Kraichnan) that occurs in the strong helical turbulent highly conducting fluid in the large-scale, nonuniform magnetic field is considered. This effect has the property of “pulling” continuous magnetic fields together in discrete structures. Our calculations for the two models of the solar convection zone have shown that, in the deep layers, there are favorable conditions for the emergence of the effect of the helical negative turbulent diffusion. Under the assumption that the lifetime of helical structures τ2 equals the lifetime of convective cells τ1, the calculated values of the coefficient of the helical negative magnetic turbulent diffusion η T α reach two-thirds of the coefficient of the positive turbulent diffusion ηT. This should greatly facilitate the self-organization of originally weak continuous magnetic fields in isolated thin magnetic flux tubes.