An investigation of north-south asynchrony of solar filament activity: Wavelet transform analyses

Monthly counts of filament numbers in the time interval of 1954 April to 2010 June are proposed to determine their phase asynchrony between the solar northern and southern hemispheres by using advanced wavelet transforms. Both the cross-wavelet transform and wavelet coherence analyses show asynchronous behaviour with strong phase mixing in the high-frequency components of hemispheric flare activity, and strong synchronous behaviour with coherent phase angles in the low-frequency components, corresponding to the period-scales around the 11-year Schwabe cycle. This study shows that the wavelet transforms techniques for the hemispheric phase analysis of solar time series is fairly useful.