Numerical simulations of altocumulus using a cloud resolving model and a mixed layer model

This paper describes the progress toward developing a parameterization of thin mid-level stratiform (altocumulus, Ac) clouds suitable for use in global climate models. 2D cloud-resolving model (CRM) simulations indicate that moist conservative variables in Ac layers are approximately well-mixed. This suggests that Ac layers may be parameterized using an elevated mixed-layer model (MLM). Therefore, an elevated MLM for Ac was developed and tested. The Ac MLM uses a method for determining the entrainment rate at the mixed layer top that is used in many MLMs of the stratocumulus-topped boundary layer (STBL). At the mixed layer base, the Ac MLM detrains at a rate that maintains a constant ratio of buoyant consumption of turbulent kinetic energy (TKE) in the subcloud layer to buoyant production in the cloud layer. To test the Ac MLM, results from it were compared to those from a CRM for a thin Ac layer and a thick Ac layer. The comparisons were good for the cloud top, cloud base, and mixed layer base heights, and fair for the liquid water path (LWP).