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(follow the model version links below for more details)

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

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.

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

Model version	Implement. date in S2S	Time range	Resolution	Ens. Size	Frequency	Re-forecasts	Rfc period	Rfc frequency	Rfc size	Ocean resolution	Active Sea Ice
GEPS2103	30/03/2021	d 0-34	Tl479/Tl319L128	49+1	weekly (Wed) lagged eps created from 2 runs (*5)	fixed	1981-2020 (model version date 31/03/2021)	2/month (always on the 15th and the last day of month *3)	12+1	N/A	N/A
GEPS2003	24/03/2020	d 0-34	Tl479/Tl319L100	49+1	weekly (Wed) lagged eps created from 4 runs (*4)	fixed	1981-2010 (model version date 31/03/2020)	2/month (always on the 15th and the last day of month *3)	12+1	N/A	N/A
GEPS1701	22/03/2017	d 0-34	Tl479/Tl319L100	49+1	weekly *(Wed) lagged eps created from 4 runs (4)**	fixed	1981-2012 (model version date 31/01/2017)	3/month (always on the 10th, 20th and the last day of month *3)	4+1	N/A	N/A
GSM1403C	06/01/2015	d 0-34	Tl319/L60	24+1	2/week (Tue, Wed)	fixed	1981-2010 (model version date 04/03/2014)	3/month (always on the 10th, 20th and the last day of month *3)	4+1	N/A	N/A