JMA Model

Description of the model changes

(follow the model version links below for more details)

GEPS2103

• The new JMA real-time ensemble system includes 2 start dates (Tuesdays and Wednesdays at 12Z) instead of the previous 4 runs (see the description in GEPS1701 below). The ensemble size is 25 members for both days and the resulting new lagged ensemble for S2S is a single 50-member ensemble starting on Wednesdays at 12Z.
• operational from 30 Mar 2021 

GEPS2003

• two-tiered Sea Surface Temperature (SST) method is implemented in addition to improved physical parameterization schemes in the forecast model. In this approach, the oceanic lower-boundary condition is relaxed from the anomaly-fixed SST to the ensemble-mean SST based on prediction using the Seasonal Ensemble Prediction System (Seasonal EPS).

• There is no change in the number of fields for real-time data but the number of reforecast ensemble members is  increased from 5 to 13, and the number of frequency is reduced from 3 to 2 per month.

• operational from 24 Mar 2020 

GEPS1701

• The new JMA real-time ensemble system includes 4 start dates (Tuesdays at 00Z and 12Z + Wednesdays at 00Z + 12Z) instead of the previous 2 only (25-member ensembles starting on Tuesday 12Z and Wednesday 12 Z). The ensemble size is 13 members for Tuesdays 12Z and Wednesdays 00 and 12Z and 11 members for Tuesdays 00Z. Because the usage of such data  would be very difficult for users, a lagged ensemble  is being created for S2S archive instead. The resulting new lagged ensemble is a single 50-member ensemble starting on Wednesdays at 12Z

• operational from 22 Mar 2017 

GSM1403C

• operational from 06 Jan 2015

Overview of the model changes