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Principal Component Analysis of Background and Sunspot Magnetic Field Variations During Solar Cycles 21-23 View all abstracts by submitter

Valentina Zharkova   Submitted: 2012-07-05 06:42

The aim of this paper is to derive principal components (PCs) in variations of (a) the solar background magnetic field (SBMF) measured by the Wilcox Solar Observatory with low spatial resolution for solar cycles 21-23, and, (b) the sunspot magnetic field (SMF) in cycle 23 obtained by SOHO/MDI. For reduction of the component dimensions, the Principal Component Analysis (PCA) is carried out to identify global patterns in the data and to detect the pairs of principal components and corresponding empirical orthogonal functions (EOFs). PCA analysis reveals two main temporal PCs in SBMF of opposite polarities originating in the opposite hemispheres and running noticeably off-phase (with about a two and half year delay), with their maximums overlapping in the most active hemisphere for a given cycle. Their maximum magnitudes are reduced by factor 3 from cycle 21 to 23 overlapping in the Northern hemisphere for cycle 21, the Southern one in cycle 22 and in the Northern again in cycle 23. The reduction of magnitudes and slopes of the maximums of the SBMF waves from cycle 21 towards cycle 23 leads us to expect lower magnitudes of the SBMF wave in cycle 24. Also PCA allowed us to detect 4 pairs of EOFs in the SBMF latitudinal components: the two main latitudinal EOFs attributed to symmetric and another three pairs of EOFs assigned to asymmetric types of meridional flows. The results allow us to postulate the existence of dipole and quadruple (or triple dipole) magnetic structures in the SBMF, which varies from cycle to cycle and takes the form of two waves travelling off phase, with a phase shift of one quarter of the 11 year period. Similar PC and EOF components were found in temporal and latitudinal distributions of the sunspot magnetic field for cycle 23 revealing the polarities opposite to the SBMF polarities and double maximum in time or maximums in latitude corresponding to the maximums of the SBMF PC residuals or minimums in SBMF EOFs, respectively. This allows to suggest that the SBMF waves also modulate the occurrence and magnitudes of sunspot magnetic field in time and latitude.

Authors: Zharkova V.V., Shepperd, S.J. and Zharkov S.I.
Projects: SoHO-MDI

Publication Status: 2012, MNRAS, in press
Last Modified: 2012-07-05 07:17
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