Key points are not available for this paper at this time.
Abstract The theory of the mass‐flux approach to parametrization of convective momentum‐transport is presented. A cloud‐resolving model is used to simulate momentum transport by ensembles of deep convective clouds in two very different regimes: a mid‐latitude cold‐air outbreak, and tropical convection forced by convergence. Idealized, unidirectional, wind‐profiles are used to simplify interpretation of the results. Diagnostics relevant to the parametrization problem are presented, and it is shown that, for both regimes, the approximations inherent in the parametrization equations are reasonable. the pressure gradients inside clouds play an important role in determining horizontal velocities in the clouds. For the cold‐air outbreak with linear shear, the results suggest that these pressure gradients are proportional to the shear and to the up/downdraught mass‐fluxes. Sensitivity studies suggest that the results are not very sensitive to resolution or parametrization of subgrid‐scale processes, giving some confidence that the results are reasonably accurate. For the tropical case with a low‐level jet, the pressure gradients change sign with the wind shear. In part II of this paper, these results will be used to develop and validate a mass‐flux parametrization of convective momentum‐transport which is tested in single column and global versions of the Meteorological Office Unified Model.
Kershaw et al. (Tue,) studied this question.