  Contex: Solar magnetic activity exhibits variations with periods between
1.5--4 years, the so-called quasi-biennial oscillations (QBOs), in addition to
the well-known 11-year Schwabe cycles. Solar dynamo is thought to be the
responsible mechanism for generation of the QBOs.
  Aims: In this work, we analyse sunspot areas to investigate the spatial and
temporal behaviour of the QBO signal and study the responsible physical
mechanisms using simulations from fully nonlinear mean-field flux-transport
dynamos.
  Methods: We investigated the behaviour of the QBOs in the sunspot area data
in full disk, and northern and southern hemispheres, using wavelet and Fourier
analyses. We also ran solar dynamos with two different approaches to generating
a poloidal field from an existing toroidal field, Babcock-Leighton and
turbulent $\alpha$ mechanisms. We then studied the simulated magnetic field
strengths as well as meridional circulation and differential rotation rates
using the same methods.
  Results: The results from the sunspot areas show that the QBOs are present in
the full disk and hemispheric sunspot areas and they show slightly different
spatial and temporal behaviours, indicating a slightly decoupled solar
hemispheres. The QBO signal is generally intermittent and in-phase with the
sunspot area data, surfacing when the solar activity is in maximum. The results
from the BL-dynamos showed that they are neither capable of generating the
slightly decoupled behaviour of solar hemispheres nor can they generate
QBO-like signals. The turbulent $\alpha$-dynamos, on the other hand, generated
decoupled 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 the
observed temporal and spatial behaviour of the QBO signal compared with those
from the BL-dynamos.
