Vortices on the surface of normal He I generated by the Rayleigh–Bénard thermogravitational convection in the bulk of a liquid

It has been experimentally found that the appearance of the Rayleigh–Bénard thermogravitational convection in the bulk of a normal helium He-I layer heated from above in an immobile working vessel at temperatures close to the critical temperature $T_\lambda$ is accompanied by the generation of vortices on the free surface of He-I. The interaction of these vortices between each other and with vertical vortex structures, which are formed in the bulk of the layer in the process of establishment of turbulent Rayleigh–Bénard thermogravitational convection, results in the appearance of large-scale vortices (vortex dipole) on the surface. Rayleigh–Bénard thermogravitational convection in the bulk of the liquid layer heated above 2.3 K decreases rapidly with the time. In the absence of pumping, in the temperature range 2.6–3.3 K, the maximum energies of large-scale vortices on the surface in the k space decrease with time as $E_{\mathrm{max}}\sim t^{-1}$.