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A.C. Cadavid, J.K. Lawrence (California State University, Northridge), A. Ruzmaikin (Jet Propulsion Laboratoy)
We carried out a principal component analysis (PCA) on sequences of NSO magnetic flux synoptic maps by Carrington rotation. Two data sets were investigated: (i) a sequence of 364 images from Carrington rotation 1625 to 2007, with image size 360 x 180 pixels (1 degree/pixel in longitude and sin(latitude)*90 in latitude for both hemispheres); (ii) a sequence of 79 higher resolution maps of size 1800 x 900 pixels starting at Carrington rotation 1913. The PCA of a time series yields an eigenvalue spectrum, the corresponding eigenfunctions (modes or “empirical orthogonal functions” (EOFs)), and the principal components which describe the time evolution of the modes. The dominant EOFs are associated with those structures that remain spatially coherent throughout intervals of the time series, and correspond to the functions with the highest eigenvalues. If the eigenvalue spectrum is dominated by only a few large members, then the corresponding few EOFs will mainly characterize the data. The rest will contain transient fluctuations. We apply the technique to the two dimensional maps and determine which EOFs dominate during different times of the solar cycle. We find that the dominant modes are associated with the active part of the cycle as expected, while the weaker modes characterize the quiet periods. The increasing and declining phases are associated with modes of intermediate eigenvalues. We reconstruct the time series by projecting onto the three classes of modes and investigate the probability distribution function (PDF) of “projected” magnetic flux. We compare these results to the PDFs obtained from artificial data generated by dynamo models. This work was supported in part by Grant NASA-NAG5-10880. NSO/Kitt Peak data used here are produced cooperatively by NSF/NOAO, NASA/GSFC, and NOAA/SEL.
The author(s) of this abstract have provided an email address for comments about the abstract: ana.cadavid@csun.edu
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Bulletin of the American Astronomical Society, 36 #2
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