Between a Cloud-resolving Model and a Steady Plume: Uses of a Time-dependent Anelastic Convective Entity (ACE) Model

A model intermediate in complexity between a cloud-resolving model and the steady-plume models typical of convective parameterizations can be useful as a process model, and arguably as a potential class of convective parameterization. Here we discuss applications of a self-consistent solution for the anelastic equations for tracer and mass flux budgets within a chosen geometry such as a column with potentially complex cross-section, and including the possibility of embedding such solutions within each other or adding neighbor interactions. The key additions to this formulation include a nonlocal representation of nonhydrostatic perturbation pressure as well as entrainment mixing that is dynamically consistent with the mass flux structure.

Features of convection where such a system yields insight include:

1. Convective inhibition (CIN) is a concept based on small parcels. For convective entities containing horizontal scales not small compared to the depth of the CIN layer or the distance to the surface, the apparent inhibition can be much smaller or even negligible.
2. This is relevant for the nighttime convection problem—convection can be initiated by forcing smaller than anticipated based on CIN value.
3. The convective cold top—a sharp cold layer that typically occurs just above and below the top of convection—changes over the lifetime of the convective entity, but can arise with relatively simple balances.
4. Upper-level detrainment of saturated air and condensate interacts with horizontal adjustment processes and subsequent evolution of a stratiform layer.
5. The entrainment varies in time with the evolution of the convective entity—including the vertical dependence of entrainment. For certain purposes, this can be mimicked by a time-constant entrainment, but this cannot capture all aspects of the solution.
6. Dynamic entrainment can yield chain-of-thermal evolution even in a 1-D time-dependent solution.
7. Substantial timelags for development of convection and complex temporal evolution due to hydrometeor loading can occur even in relatively simple geometry.