Atmospheric convection in which the phase changes of water play an appreciable role. All cumuliform clouds are manifestations of moist convection. The enthalpy exchange between condensing water vapor or freezing liquid water and air (see latent heat) is a major contributor to the positive buoyancy of updrafts, while the reverse exchange between air and evaporating water or melting ice contributes strongly to the negative buoyancy of downdrafts.