34th Solar Physics Division Meeting, June 2003
Session 7 Photosphere and Chromosphere I
Poster, Monday, June 16, 2003, 3:30-5:00pm, Mezzanine

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[7.08] H\alpha Full Disk Observations of Chromospheric Differential Rotation

G. A. Smith, J. Varsik, J. Nenow, W. H. Marquette, H. Wang, C. Denker (NJIT/CFSR/BBSO)

We studied the solar chromospheric rotation profile using full-disk H\alpha images of the Sun obtained at the Big Bear Solar Observatory (BBSO). The method is based on Local Correlation Tracking (LCT). As a unique feature the entire full-disk image is used, i.~e., quiet sun as well as solar active regions, whereas most other methods rely on images of distinct individual features such as filaments, plages, and sunspots. Six months of H\alpha full-disk data sets from June to December 2001, which consists of 600 to 800 daily images at 30~s to 60~s cadence, have been processed and analyzed. The images were checked for a number of problems, including overexposure, underexposure, and skewed images. All images were normalized by having the solar disk recentered, the dark frame subtracted, and the limb darkening function calculated and subtracted from the image. The images are locally cross-correlated with each other to find the displacements between them. The angular velocities are projected onto the central meridian and a differential rotation profile is fitted to the data (either as Legendre polynomials or as polynomials in \sin2n\theta, \quad n=0,1, 2, \ldots, where \theta is the heliographic longitude). The currently used settings in the processing of the six months data were optimized for both accuracy and speed. A number of different parameters were experimented with, such as various grid sizes, grid spacing, sampling window sizes, weighing functions and also different implementations of cross-correlation algorithms, to find the best combination.

This work was supported by NSF under grant ATM 00-86999, ATM 00-76602, and ATM 02-36945 and by NASA under grant NAG 5-9682.


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