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| Paper: |
The Solar Rotation and Its Evolution during Cycle 23 |
| Volume: |
462, Progress in Solar/Stellar Physics with Helio- and Asteroseismology |
| Page: |
267 |
| Authors: |
Korzennik, S. G.; Eff-Darwich, A. |
| Abstract: |
We present the most exhaustive and accurate inferences of the internal solar
rotation rate and its evolution during solar cycle 23. A full solar cycle of
Michelson Doppler Imager
(MDI) observations has been analyzed using our state of the art fitting
methodology. Time series of various lengths have been fitted, from a single
4608-day long epoch (64 × 72 day or 12.6 year) down to 64 separate
segments for the traditional 72-day long epochs. We used time series of
spherical harmonic coefficients computed by the MDI group but using an
improved spatial decomposition. This decomposition now 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 effect of
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 for
that epoch and all available segments, including the MDI and
Global Oscillation Network Group (GONG) pipe-line
sets. The improved inversion method we used is an iterative methodology
based on a regularized least-squares. It implements a model grid optimization
derived from the actual information in the input set. This optimized model
grid is itself irregular, namely with a variable number of latitudes at
different depths.
We present the most accurate mean rotation rate, to date. We also focus on
the change of the rotation rate with activity levels and how well these
changes are assessed at high latitudes and below the surface, down to the
base of the convection zone. |
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