	Forecast / Analysis	Number of members	Horizontal resolution	Vertical levels	Pressure at model top (hPa)	Perturbation models
HRES Atmospheric Model high resolution Data Graphical products	Forecast 0–10 days	1	Native ⁽¹⁾: O1280 ~9km Interpolated ⁽²⁾: 0.1° ~9km	137	0.01 hPa	No
ENS Ensemble - Atmospheric Model Data Graphical products	Forecast 0–15 days	51	Day 0-15 Native ⁽¹⁾: O640 ~18km Interpolated ⁽²⁾:0.2°	137	0.01 hPa	Yes⁽⁴⁾
ENS Extended Atmospheric Model Extended forecast (monthly) Data Graphical products	Forecast 16–46 days run twice a week	51	Native (1): O320 ~36km Interpolated ⁽²⁾: 0.4°	137	0.01 hPa	Yes ⁽⁴⁾
4DVAR 4-Dimensional data assimilation Data (See Analysis in HRES) Graphical products	Analysis	1	N255/N319/N399/N399 inner loop minimisations 4 outer loops at O1280 resolution	137	0.01 hPa	No
EDA Ensemble of data assimilations Data	Analysis	51	N191/N191 inner loop minimisations 2 outer loops at O640 resolution	137	0.01 hPa	Yes ⁽⁵⁾
SEAS5 2017 version Cycle 43r1 Seasonal forecast Data Graphical products	Forecast long-range forecast run monthly from 0 to 7 months annual range forecast run quarterly from 0 to 13 months	51 15	Native ⁽¹⁾:O320 ~36km Interpolated ⁽²⁾: 0.4°	91	0.01 hPa	Yes ⁽⁴⁾

Ensemble and

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seasonal re-forecasts

Table 1b: Key characteristics of the ENS and SEAS re-forecasts of the ECMWF IFS

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