On the Definition of the Cloud Water Content Fluctuations and Its Effects on the Computation of a Second-Order Liquid Water Correlation

Abstract

In subgrid-scale condensation schemes of cloud models, the majority of previous authors have relied on results presented in a paper by Bougeault. In the present paper, second-order liquid water correlations are restated that differ from the former paper but are coherent with the corrigendum of Mellor. These differences are explained here through two different underlying definitions of cloud water content fluctuations; they can be summarized by whether or not unsaturated air within a grid box contributes to the eddy flux of the cloud water content. Taking into account the issue mentioned above, the ?buoyancy flux? is also derived. Although the full impact of these changes has not been evaluated here, it may become important for future global cloud-resolving climate models.