Seasonal Prediction of Tropical Cyclones in a New Non-hydrostatic GFDL HiRAM

A new version of Geophysical Fluid Dynamics Laboratory (GFDL) High-Resolution Atmospheric Model (HiRAM) using the non-hydrostatic finite-volume cubed-sphere dynamical core (FV3) is being developed for tropical cyclone (TC) studies. This model marks a radical shift from the hydrostatic dynamics used by previous GFDL global models. It uses a C384 (25 km) horizontal grid with 63 vertical levels, and includes many updates in the cloud microphysics and cloud convective parameterization. A new land model configuration with the effects of lakes and rivers, as well as many other land-surface process improvements is also tested and included. With the finer vertical resolution and higher model top, the improved modeling system can now better resolve the upper troposphere and the stratosphere, thus improving the simulation of the tropical quasi-biennial oscillation (QBO) and Madden-Julian Oscillation (MJO), which may play important roles in the seasonal TC activities. The non-hydrostatic model greatly reduces the positive TC count bias in the western Pacific shown in the previous dynamical TC seasonal prediction studies. The forecast skill and other related results of the new HiRAM for the past decade and recent seasons, using the persistent sea surface temperature assumption, will be presented.