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Does the High-latitude Solar Activity Exhibit Quasi-biennial Oscillations?
Author: | Update time:2020-05-15           | Print | Close | Text Size: A A A

From a recent study published on Monthly Notices of the Royal Astronomical Society, solar physicists know more about the quasi-biennial oscillations of solar activity at high latitudes. Dr. DENG Linhua, from Yunnan Observatories of Chinese Academy of Sciences, led the research.

Quasi-biennial oscillations (QBOs) are considered as a fundamental mode of solar magnetic activity at low latitudes. However, the evolutionary aspect and the hemispheric distribution of solar QBOs at high latitudes are rarely studied. Therefore, it is necessary to study the spatial and temporal behaviors of solar QBOs at different latitudes.

The long-term data sets of the polar faculae were taken from the Mitaka of the National Astronomical Observatory of Japan. Polar faculae have been recorded on the sunspot sketches made with the Zeiss 20cm refractor at Mitaka. Individual observations have taken 30 minutes or so, and faculae have lift times of similar length, so that the polar faculae count represent snap shots at the time of observation.

For studying the spatial distribution of solar QBOs at high latitudes, a novel time-frequency analysis technique called the synchrosqueezed wavelet transform is applied. This method has a firm theoretical foundation, so the intrinsic modes extracted by this technique can be explained from a physical point of view. Moreover, it can locate the frequency components with a high spectrum resolution, and it produces a sharper time-frequency map of the data sets.

It is found that apart from the 22-year Hale cycle, the 17-year extended activity cycle, and the 11-year Schwabe cycle, the QBOs have been estimated as a prominent timescale of solar magnetic activity at high latitudes. The QBOs of the polar faculae are coherent in the two hemispheres, but the temporal (phase) and the spatial (amplitude) variations of solar QBOs occur unevenly on both hemispheres. The temporal variations of solar QBOs at high latitudes are different from those at low latitudes. Such a difference can be interpreted as phase asynchrony between the polar faculae and the sunspot numbers.

The temporal and spatial distribution, such as the periodic values of solar magnetic activity and the hemispheric asymmetric distribution at high latitudes, is thought to have little or no relation to that at low latitudes. Because the solar magnetic fields at high latitudes might have two origins: the flux emergence of the magnetic activity from the interior of the Sun, and the drift of the magnetic field towards the poles at low latitudes.

The main results may help to better reveal the physical origin of the spatial distribution of solar QBOs at high latitudes and might help to predict their dynamical behavior. In addition, solar QBOs at high latitudes might be directly connected with other astrophysical fields, such as the QBOs of solar neutrino fluxes, the modulation of cosmic ray flux in interplanetary space, and so on. However, the exact relationship between them deserves a more in-depth investigation in the future.



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