Temporal variation of angular momentum in the convection zone

Abstract

We derive the angular momentum as a function of radius and time with the help of the rotation rates resulting from inversions of helioseimic data obtained from the Global Oscillation Network Group (GONG) and the Michelson Doppler Imager (MDI) and the density distribution from a model of the Sun. The angular momentum as a function of radius shows the strongest temporal variation near the base of the convection zone. This variation extends into the lower convection zone and into the radiative interior and is related to the 1.3-yr periodicity found in the equatorial rotation rate of the tachocline. In the upper convection zone, we find a small systematic variation of the angular momentum that is related to torsional oscillations. The angular momentum integrated from the surface to a lower limit in the upper convection zone provides a hint that the torsional oscillation pattern extends deep into the convection zone. With the lower limit of integration placed in the lower half of the convection zone, the angular momentum fluctuates about the mean without apparent trend, i.e. the angular momentum is conserved within the measurement errors. However, when integrated over the layers slightly below the convection zone, the angular momentum shows the 1.3-yr period and hints at a long-term trend which might be related to the solar activity cycle.