Improvement of the precipitation processes in the JMA high-resolution global NWP model and Its impact study for tropical cyclone cases

The Japan Meteorological Agency (JMA) has a plan to enhance the horizontal resolution (from 60 km to 20 km) and the vertical resolution (from 40 layers to 60 layers) of the operational Global Spectral Model (GSM). Since a different model resolution chances a precipitation balance in grid and subgrid scale condensation processes, we need to modify the precipitation processes to suit the 20km GSM.

Through several case studies, we investigate the cloud and precipitation characteristics with the 20 km GSM and try to improve the precipitation processes (grid scale condensation and subgrid scale deep and shallow cumulus etc.) of the model. Since the resolution enhancement aims improving the model's ability to forecast high impact weather such as tropical cyclones (TCs), we investigate how the precipitation processes of the model affect the simulated TC structures.

In this study, we find that the modification of the precipitation processes provides a distinct and improved TC eyewall structure according to the results of the comparison between GSM simulated images and MTSAT satellite images.