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Contex: Solar magnetic activity exhibits variations with periods between1.5--4 years, the so-called quasi-biennial oscillations (QBOs), in addition tothe well-known 11-year Schwabe cycles. Solar dynamo is thought to be theresponsible mechanism for generation of the QBOs.  Aims: In this work, we analyse sunspot areas to investigate the spatial andtemporal behaviour of the QBO signal and study the responsible physicalmechanisms using simulations from fully nonlinear mean-field flux-transportdynamos.  Methods: We investigated the behaviour of the QBOs in the sunspot area datain full disk, and northern and southern hemispheres, using wavelet and Fourieranalyses. We also ran solar dynamos with two different approaches to generatinga poloidal field from an existing toroidal field, Babcock-Leighton andturbulent $\alpha$ mechanisms. We then studied the simulated magnetic fieldstrengths as well as meridional circulation and differential rotation ratesusing the same methods.  Results: The results from the sunspot areas show that the QBOs are present inthe full disk and hemispheric sunspot areas and they show slightly differentspatial and temporal behaviours, indicating a slightly decoupled solarhemispheres. The QBO signal is generally intermittent and in-phase with thesunspot area data, surfacing when the solar activity is in maximum. The resultsfrom the BL-dynamos showed that they are neither capable of generating theslightly decoupled behaviour of solar hemispheres nor can they generateQBO-like signals. The turbulent $\alpha$-dynamos, on the other hand, generateddecoupled hemispheres and some QBO-like shorter cycles.  Conclusions: In conclusion, our simulations show that the turbulent$\alpha$-dynamos with the Lorentz force seems more efficient in generating theobserved temporal and spatial behaviour of the QBO signal compared with thosefrom the BL-dynamos.

Nonlinear dynamo models using quasi-biennial oscillations constrained by sunspot area data