A Combined Analysis of the Observational Aspects of the Quasi-biennial Oscillation in Solar Magnetic Activity

Solar quasi-biennial oscillations (QBOs) with the time scale of 0.6-4 yrs appear to be a basic feature of the Sun's activity. Observational aspects of QBOs are reviewed on the basis of recent publications. Solar QBOs are shown to be ubiquitous and very variable. We demonstrate that many features of QBOs are common to different observations. These features include variable periodicity and intermittence with signs of stochastisity, a presence at all levels of the solar atmosphere and even in the convective zone, independent development in the northern and southern solar hemispheres, most pronounced amplitudes during the maximum phase of the 11-yr cycle and the transition of QBOs into interplanetary space. Temporal weakening of solar activity around the maximum of the 11-yr cycle (Gnevyshev Gap) can be considered an integral part of QBOs. The exact mechanism by which the solar QBO is produced is poorly understood. We describe some of the most plausible theoretical mechanisms and discuss observational features that support/contradict the theory. QBOs have an important meaning as a benchmark of solar activity, not only for investigation of the solar dynamo but also in terms of space weather.