Viewing the “rush to the poles” through phase analysis

Abstract

At mid and low heliographic latitudes, filament activity shifts equatorward starting from the beginning of the solar cycle. At high latitudes, it migrates poleward. Solar filaments exhibit the “rush to the poles” close to solar maximum, when the solar polar magnetic field reverses polarity. In order to better understand the behavior of the “rush to the poles,” we used cross-correlation analysis and wavelet transform methods for investigating the periodic characteristics and the phase relationship between two groups of the solar filaments at high latitudes observed during the period from 1919 March to 1989 December. The length of the solar cycle derived from the continuous wavelet transform is a function of latitude, but still shows a significant 11-yr cycle. The most significant periods of the solar filaments, respectively at higher latitudes than 50° and 60°, are 10.77 and 10.62 yr, using the wavelet transform method. From the cross-correlation analysis, the solar filaments at higher latitudes than 50° have a lead of six months with respect to those at higher latitudes than 60°. Different solar cycles exhibited different phase relationships between the two groups of solar filaments. The analysis of the cross-wavelet transform also indicates that the solar filaments at higher latitudes than 50° lead those at higher latitudes than 60° in the entire time interval. The relationship between the phase difference of the two groups of solar filaments and the intensity of solar activity is also discussed. What is more, the poleward shifting speeds are estimated.

What Causes the Inter-Solar-Cycle Variation of Total Solar Irradiance?

“…The XWT and WTC are widely used to analyze the nonlinear behavior and expose common power and relative phase in time-frequency space between the two time series (Grinsted et al 2004;Li 2008;Li et al 2009;Deng et al 2012;Kong et al 2014 (Grinsted et al 2004;Li et al 2009;Deng et al 2013). Cross wavelet power reveals areas with high common power.…”