Other
Scientific paper
May 2005
adsabs.harvard.edu/cgi-bin/nph-data_query?bibcode=2005agusmsp21b..07c&link_type=abstract
American Geophysical Union, Spring Meeting 2005, abstract #SP21B-07
Other
7509 Corona, 7524 Magnetic Fields
Scientific paper
Principal component analysis (PCA) offers a way to extract those structures that remain spatially coherent throughout a time series. We apply this method to a ~ 28 year time series of Wilcox Solar Observatory Carrington rotation maps (CR) of the 3.25 R coronal source surface field obtained via a potential field extrapolation. We find that over 99% of the variance is contained in the first eight modes. Mode 1, carrying 81.5% of the variance, and modes 2 and 3 containing 13% of the variance, have "dipole" structures. Modes 4-8, with a "quadruple" structure, contain 4.5% of the variance. The principal components (PCs) give the time dependence of the modes. We combine the PCs of modes 2 and 3 to get the amplitude and phase of a structure that behaves essentially as a dipole in the equatorial plane. During activity minima the structure is relatively weak and rotates at the 27.275 day Carrington rate. During the active periods of cycles 21 and 22 the amplitude is large and highly intermittent, and the dipole rotates more rapidly than the Carrington rate with a synodic period of 26.6 days. During cycle 23, however, the dipole moves backward in Carrington longitude with a synodic period of 27.8 days. The average of these is ~ 27.0 days, though this is actually realized only sporadically. The phase changes that occur at shorter time scales and that coincide with intermittent changes in the dipole amplitude seem to represent essentially random effects of the passage of the magnetic field through the convection zone. While the lower modes tend to lock the hemispheres together the higher modes present separate Northern and Southern hemisphere quadrupole-type patterns that drift in Carrington longitude similarly to the equatorial dipole. Over some periods the drift in each hemisphere closely tracks the other over a wide range of timescales. However, there are large, decadal-scale excursions in which first one hemisphere leads in phase by 3 or 4 rotations and then the other leads by a similar amount.
Cadavid Carlos A.
Lawrence John K.
Ruzmaikin Aleksandr
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