The Solar Subsurface Radial Gradient of Angular Velocity as Revealed by Ring Diagram Analysis
Résumé
We have estimated the radial gradient of angular velocity in the near subsurface layers of the sun for the period 07/2001-07/2007 which covers 80 Carrington rotations, starts at the maximum of cycle 23 and ends at its minimum. This analysis confirms that, on average, the radial gradient of angular velocity remains negative and roughly constant between 0.980 and 0.991 Rsun below 40° of latitude. The extension of ring analysis up to 60° over two periods covering three Carrington rotations each shows a positive gradient at this latitude which tends to confirm the sign reversal revealed by the analysis of MDI f modes (Corbard & Thompson 2002). Finally, we report an enhancement of the radial gradient around 35° and 0.990 Rsun at the beginning of 2007 which corresponds to the beginning of the new cycle 24.