Entrainment Through the Top of a Heavy Gas Cloud, Numerical Treatment

After termination of the slumping phase of a heavy gas cloud, the height slowly starts to grow again. In Jensen (1981) it was shown that this cannot be the result of entrainment through the side wall but must be due to entrainment through the cloud top. Further, conservation equations for the density excess, Δρ, of the cloud relative to ambient air as well as for temperature difference, ΔT, between cloud and surface were given. For a cold cloud, qualitative arguments were derived to the effect that the density-jump Ri-number, controlling entrainment, would vanish faster than the temperaturejump Ri-number, controlling the general level of incloud turbulence, thus predicting that vertical growth should be an accelerating function of time in this case.