  This work addresses the effect of travelling thermal waves applied at the
fluid layer surface, on the formation of global flow structures in 2D and 3D
convective systems. For a broad range of Rayleigh numbers ($10^3\leq Ra \leq
10^7$) and thermal wave frequencies ($10^{-4}\leq \Omega \leq 10^{0}$), we
investigate flows with and without imposed mean temperature gradients. Our
results confirm that the travelling thermal waves can cause zonal flows, i.e.
strong mean horizontal flows. We show that the zonal flows in diffusion
dominated regimes are driven purely by the Reynolds stresses, always travelling
retrograde, while in convection dominated regimes, mean flow advection, caused
by tilted convection cells, becomes dominant, which generally leads to prograde
mean zonal flows. By means of direct numerical simulations we validate
theoretical predictions made for the diffusion dominated regime. Furthermore,
we make use of the linear stability analysis and explain the existence of the
tilted convection cell mode. Our extensive 3D simulations support the results
for 2D flows and thus confirm the relevance of the findings for geopyhsical and
astrophysical systems.
