Convective Organization in Evolving Large-Scale Forcing Represented by a Highly Truncated Numerical Archetype

Yano, Jun-Ichi ; Moncrieff, Mitchell W.

Année de publication
Considered as a prognostic generalization of mass-flux-based convection parameterization, the highly truncated nonhydrostatic anelastic model with segmentally constant approximation (NAM-SCA) is tested with time-evolving large-scale forcing. The 20-day GATE Phase III period is taken as a major data source. The main advantage of the NAM-SCA parameterization is consistency with subgrid-scale dynamics as represented by the nonhydrostatic anelastic formulation. The approach explicitly generates important dynamical structures of convection (e.g., mesoscale circulations, cold pools) spontaneously without further tuning or treatment as additional subcomponents. As with other convection parameterizations, the numerical simulation of the precipitation rate, the apparent heat source, and the apparent moisture sink is straightforward and reasonably insensitive to the numerical procedures. However, convective momentum transport by organized convection turns out to be difficult even with NAM-SCA, especially for the inherently three-dimensional shear-parallel systems. Modifications of NAM-SCA regarding the large-scale forcing formulation improves the mesoscale momentum transport. Simulation of the full 120-day TOGA COARE period demonstrates the performance of NAM-SCA in different meteorological conditions and its capacity to operate over a longer time period.
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