Isentropic Finite Volume Dynamical Core

Numerous studies have demonstrated that vertical discretizations of atmospheric general circulation models have a significant impact on the characteristics of tracer transport and atmospheric dynamics. The NCAR Finite Volume (FV) dynamical core employs quasi-Lagrangian surfaces in the vertical which reduces all advective processes of the governing equations to 2D. Vertical transport is accounted for by an occasional remapping process to a set of layers defined by coordinate surfaces that are a function of pressure and surface pressure (a "hybrid coordinate" formulation). Although this model has quite desirable transport properties compared to many other formulations, we believe that some of the less desirable properties are attributable to the remapping to the hybrid pressure coordinate layers. A very desirable feature for the vertical discretization is that the Lagrangian model surfaces are defined by a conserved variable. Under adiabatic and inviscid processes in the atmosphere, potential temperature is conserved following the motion of fluid and isentropic surfaces correspond to material coordinates. In this study, we implement a hybrid isentropic vertical coordinate in the FV model. We will address the consequence of changing the model vertical discretization. The performance of the isentropic FV model is first assessed by conducting an idealized adiabatic baroclinic wave test case. Secondly, a suite of tests designed to examine the model behavior on tracer transport are performed. Finally, the climatology simulated by the new isentropic FV model coupled with full physics will be presented and compared with that carried out with the hybrid-pressure FV model.