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The Rotation Rate and its Evolution Derived from Improved Mode Fitting and Inversion Methodology | |
Auteur | Korzennik Sylvain |
Institution | Harvard-Smithsonian Center for Astrophysics |
Theme | Convection, dynamo and flows |
| Auteur(s) supplémentaire(s) | Eff-Darwich, Antonio |
| Institution(s) supplémentaire(s) | Instituto de Astrofisica de Canarias, Tenerife, Spain |
Abstract | We present our latest inferences of the internal solar rotation rate and its evolution during solar cycle 23. A full solar cycle of MDI observations have been analyzed using an improved fitting methodology (Korzennik (2005 and 2008). Time series of various lengths have been fitted, from a single 4,608 day long epoch (64 times 72 day or 12.6 yr) down to 63 overlapping 144-day long epochs. We used time series of spherical harmonic coefficients computed by the MDI group using their improved spatial decomposition. This decomposition includes our best estimate of the image plate scale and of the MDI instrumental image distortion. The leakage matrix used for the fitting includes the distortion of the eigenfunctions by the solar differential rotation, and the undistorted leakage matrix was itself carefully reviewed and independently recomputed. Rotation inversions were carried out for all the available mode sets, fitted for that epoch, including the MDI and GONG "pipe-line" values. The improved inversions use an iterative methodology based on a least-squares regularization, but with an optimal model grid determined by the actual information in the input set. This method now also allows us to use an optimized irregular grids, with a variable number of latitudes at different depths. |