Experimental Study of Advanced Cloud Microphysics in the U.S. Navy Global Environmental Model

The U.S. Navy's Global Environmental Model (NAVGEM) is a new generation global-weather-prediction system. It is equipped with a new dynamical core of semi-Lagrangian semi-implicit advection, enabling the integration of advanced physics parameterizations at higher grid resolutions and larger time steps than current Navy's operational system NOGAPS (using Eulerian advection). In coordinating with the need for advanced physics in the NAVGEM, a prognostic cloud model with four explicit cloud species, non-precipitating liquid water and ice, rain and snow, is being implemented and researched. The comprehensive cloud microphysics is similar to the cloud package in Navy's Coupled Ocean-Atmosphere Mesoscale Prediction System (COAMPS) but with more advanced parameterizations and is more efficient in computations. In order to maximize the performance of the cloud physics, a high-spectral resolution radiation model RRTMG (Rapid Radiation Transfer Model for Global Applications, by AER Inc.) is also being implemented into the NAVGEM to achieve effective high-order accurate cloud-radiation interactions. The new cloud physics has been intensively investigated with the radiation through a winter and a summer periods of total 8 months for its contributions to the NAVGEM overall performance in general forecast scores and hurricane track forecasts. The statistics of the new physics, obtained from the validations with conversional weather observations, compare favorably to the NOGAPS operational output. The modeled precipitation, cloud water, and radiative fluxes are further verified with satellite retrieval data and field experiment observations. The experimental tests reveal the encouraging improvement to the NAVGEM and operational NOGAPS. The new physics of cloud and radiation together provides a promising platform to extend NAVGEM's capability for long-range weather predictions and aerosol-cloud-radiation interactions.