On average, the largest convective buoyancies and vertical velocities occur in the upper troposphere. Common wisdom states that this results from the extra buoyancy provided by the latent heat of fusion. Here, we show that this is a fallacy: the profiles of convective buoyancy and vertical velocity are basically the same in a world with and without ice.
This is shown here by running large-eddy simulations of radiative-convective equilibrium with and without the latent heat of fusion. When these two "worlds" are compared, the existence of ice does increase the temperature of clouds in the upper troposphere, but it also increases the temperature of the atmosphere in lock step. This happens because convection and the atmosphere are tightly coupled, with the atmosphere adjusting its temperature profile to closely match the temperature profile of convection.
The temperature difference between a world "with ice" and a world "without ice" for (red) clouds and (black) the environment. Ice increases the temperature of clouds in the upper troposphere due to the latent heat of fusion, but the environment adjusts accordingly to ensure that the average cloud continues to have very little buoyancy.