Numerous analyses suggest the existence of various quasi-periodicities in solar activity .
The power spectrum of solar activity recorded in sunspot data is dominated by the \sim 11-year quasi-periodicity , known as the Schwabe cycle .
In the mid-term range ( 1 month – 11 years ) a pronounced variability known as a quasi-biennial oscillation ( QBO ) is widely discussed .
In the shorter time scale a pronounced peak , corresponding to the synodic solar rotation period ( \sim 27 days ) is observed .
Here we revisited the mid-term solar variability in terms of statistical dynamic of fully turbulent systems , where solid arguments are required to accept an isolated dominant frequency in a continuous ( smooth ) spectrum .
For that , we first undertook an unbiased analysis of the standard solar data , sunspot numbers and the F10.7 solar radioflux index , by applying a wavelet tool , which allows one to perform a frequency-time analysis of the signal .
Considering the spectral dynamics of solar activity cycle by cycle , we showed that no single periodicity can be separated , in a statistically significant manner , in the specified range of periods .
We examine whether a model of solar dynamo can reproduce the mid-term oscillation pattern observed in solar data .
We found that a realistically observed spectrum can be explained if small spatial ( but not temporal ) scales are effectively smoothed .
This result is important because solar activity is a global feature , although monitored via small-scale tracers like sunspots .