A vertically nested regional numerical weather prediction model with second-order closure physics

Abstract The model we describe involves a unique strategy in which a high vertical resolution grid is nested within the coarse vertical resolution grid of a regional numerical weather prediction (NWP) model. Physics computations performed on the high vertical resolution grid involve time-dependent solution of second-order turbulence equations, the transfer equations for long- and shortwave radiation, and moist thermodynamic calculations which include liquid water content and fractional cloudiness. The dynamical computations involving advection, pressure gradient, and Coriolis terms are performed on the regional model grid. The two grids interact fully each model time step. This approach represents an extension into NWP of the general practice of supplying coarse large-scale dynamical forcing to high-resolution boundary layer models. Aside from the computational savings of performing dynamical calculations only at the coarser resolution, we also avoid difficulties which can arise with high vertical-resolut...