Seasonal air temperature variations and corresponding changes in groundwater temperature cause convective movements in groundwater similar to the seasonal turnover in lakes. Numerical simulations were performed to investigate the natural conditions for thermally driven groundwater convection to take place. Thermally driven convection could be triggered by a horizontal groundwater flow. Convection then starts at a considerably lower Rayleigh number (Ra) than the general critical Rayleigh number (Rac) assuming that 10°C groundwater is cooled to 4°C, i.e. heated from below convection in porous media. This study supports the hypothesis that seasonal temperature variations, under certain conditions, initiate and drive thermal convection.

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