In a recent study published on Monthly Notices of the Royal Astronomical Society, solar physicists knew more about the quasi-biennial oscillation (QBO) behavior of solar magnetic activity in the northern and southern hemispheres. Dr. DENG Linhua, from Yunnan Observatories of the Chinese Academy of Sciences, led the research.

Solar magnetic activities have a complex dependence on time-scales ranging from several seconds to thousands of years and potentially up to millions of years. Previous studies showed that the most prominently recognized periodicities shorter than the 11-year Schwabe cycle are the solar QBO concentrated around two years (always between 1 year and 3 years), whose physical origin may be related to the dynamic process in the solar tachocline.

The phase and amplitude of solar QBO are modulated by the 11-year solar cycle, being particularly strong around the maximum phase of solar cycle. As the power spectra in the time-frequency space of solar activities are very low, so it is difficult to determine the temporal and spatial variation of solar QBO.

To add more information on the spatio-temporal distribution and the underlying processes of solar QBO in the northern and southern hemispheres, researchers focus on the solar Hα flare activity over the past four solar cycles provided by the Kandilli Observatory of Bogazici University.

Based on the statistical analysis revealed by the ensemble empirical mode decomposition, the phase and amplitude of solar oscillation modes at different timescales are discovered.

It is found that the solar QBO in the two hemispheres has a complicated phase relationship, but does not show any systematic regularity. However, for the 11-year component, the northern hemisphere begins nine months earlier than the southern one for the last forty years.

The phase and amplitude asymmetry of solar magnetic activities are an important topic of cyclic behavior that could inform modelers about the relative importance of possible mechanisms that participate in hemispheric coupling. "More observational data driven numerical simulations are required to better understand and reveal the physical process of the phase and amplitude asymmetry of solar QBO", said Dr. DENG.