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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.
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