Deep-convective vertical transport: what is mass flux?

Abstract. Conceptual basis for the convective mass flux that is used in parameterizations is reviewed from a historical perspective. The main idea of the convective mass flux formulation does not purely reside in dividing the grid-box averaged vertical velocity into several mass flux components such as convective updrafts, downdrafts, and environmental subsidence. The main point rather resides on assuming different vertical profiles for transported quantities for different components. From this point of view, the best way to turn off the convective transport of chemical species is to set the vertical profile of chemical species within convective components (both updrafts and downdrafts) equal to that of the environment. This procedure turns out to be equivalent of simply turning off a standard convective chemical transport package.