Figure 7: Variation in the deep-rooted small-scale solar magnetic features over solar cycle 23.
From: The solar magnetic activity band interaction and instabilities that shape quasi-periodic variability
(a) Variation in the density of giant convective cell vertices (g-nodes) averaged over 45–50° latitude in the northern (red) and southern (blue) hemispheres from the SOHO Michelson Doppler Imager and SDO Helioseismic Magnetic Imager—markers of deep-rooted solar magnetism that belong to the toroidal magnetic flux systems of the 22-year magnetic activity cycle2. The small dots are individual daily averages, while the thick lines are the corresponding 50-day running average. As in Fig. 6, the variable phase of the timeseries in each hemisphere is strongly indicative of a solar origin for these phenomena and not some orbital or Sun–spacecraft distance variability. The periods where the hemispheres vary in phase correspond to the times of strongest modulation in the energetic parameters shown in the figures above. (b,c) Fast Fourier transform (FFT) power spectra of the northern and southern hemispheric g-node timeseries, when compared with counterparts for the daily hemispheric sunspot number, respectively, (Fig. 3) show broad peaks of significant power occurring throughout the timeseries, especially those centred on 330 days, 30 days and 15 days in the shaded regions.
