Coherent structures in the dynamics of the large-scale solar magnetic field

Abstract

Variations in the mean solar magnetic field (MSMF) are studied in both the frequency-time and longitude-time domains. A wavelet analysis of the MSMF clearly demonstrates that variations in the mean field are not stationary. Combined with longitude-time diagrams for the background solar magnetic field (BSMF), the analysis reveals the emergence of the background field, which occurs discretely at intervals of 1.5–2 years. Based on an analysis of the fine structure in MSMF variations, we develop a numerical technique to study timedependent heliographic-longitude distribution of the large-scale magnetic field. A detailed picture of the rotation of the large-scale magnetic field is derived for activity cycles 20–23. Coherent structures are detected in longitude-time diagrams obtained by deconvolving the MSMF series. These structures are related to discrete rigid-rotation modes of the large-scale magnetic fields. Various rotational modes coexist and replace one another. During the phase of activity growth, modes with periods of 27.8–28.5 days dominate, whereas a mode with a rotational period of about 27 days dominates during the decline phase. Occasionally, modes with periods of 29–30 days appear. Most structures in the longitude-time MSMF distribution correspond to similar structures in the BSMF distribution for the northern or southern hemisphere. Chronologically, the emergence of the BSMF has frequently been accompanied by changes in the solar rotational regime and has been correlated with variations in the polarity asymmetry in the course of the 11-year activity cycle.