Alpha-effect, helicity and angular momentum transport for a magnetically driven turbulence in the solar convection zone

For a given field of magnetic fluctuations the dynamo-alpha, as well as the kinetic and current helicities, have been computed. assuming that turbulen ce is subject to magnetic buoyancy and global rotation. The sign of the dyn amo-alpha is positive in the northern hemisphere and negative in the southe rn hemisphere. The kinetic helicity has just the same latitudinal distribut ion as the alpha -effect, indeed there is no minus sign between the dynamo- alpha and the kinetic helicity. Also the current helicity [j . B] changes i ts sign at the equator. It is negative in the northern hemisphere and posit ive in the southern hemisphere. Our current helicities (due to fluctuations ) and alpha -effects are thus always out of phase, this confirming a previo us result of Keinigs (1983) and Radler and Seehafer (1990). The signs of th e alpha -effect and both helicities correspond to the numerical simulations by Brandenburg and Schmitt (1998). We have also computed the turbulent ang ular momentum transport, which proves to be always inwards, as in hydrodyna mic simulations without magnetic fields (Chau, 1999). Thus we can easily ex plain why, in the supergranulation zone, deeper layers appear to rotate fas ter than the solar surface plasma, or why in the solar tachocline at high-l atitudes the angular velocity decreases outwards. The dynamo number derived from the observed current helicity reveals the alpha -effect to be rather small, unless the magnetic eddy diffusivity is not as low as the sunspot de cay suggests (i.e., 10(11) cm(2) s(-1)).