Upgrades to the Japan Meteorological Agency’s Global Spectral Model and Global Ensemble Prediction System

The Japan Meteorological Agency (JMA) upgraded its Global Spectral Model (GSM) and Global Ensemble Prediction System (GEPS) on 14 March 2023.

Enhancements include:

Increased GSM horizontal resolution
- Incorporation of quadratic grid formation from TL959 (linear, approx. 20 km grid spacing) to TQ959 (quadratic, approx. 13 km grid spacing) with refinement of numerical diffusion in the model and filters for mean orography
Change of source data set for orographic ancillary files from GTOPO30 to MERIT DEM + RAMP2
Revision of physical processes for variables including non-orographic gravity waves, boundary layers, orographic drag and radiation
Enhancement for lake surface processing
Revision of global snow depth analysis
Assimilation of Suomi-NPP and NOAA-20/VIIRS AMVs
Expansion of the two-tiered sea surface temperature method using the Seasonal Ensemble Prediction System from tropical and sub-tropical oceans to the whole globe for GEPS

These upgrades are expected to enhance user operations.