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Seasonal re-forecasts for the S-M-climate

The set of re-forecasts is based on using the same calendar start date (the 1st of each month) as the seasonal run in question.  Re-forecasts are created using the same calendar start dates during the 24 year period: Jan 1993 to Dec 2016.  

Each re-forecast consists of an 11-member ensemble (1 control and 10 perturbed members).  Therefore altogether 20 years x 3 runs x 11 ENS members = 660 re-forecast values are available to define the ER-M-climate for each forecast parameter, forecast lead-time, calendar start date and location.  These are used to define the ER-M-climate.

The set of re-forecasts is made up from:

• a set of re-forecasts using the same calendar start dates for each of the last 20 years.three consecutive re-forecasts (covering a 1 week period), the middle one of which corresponds to the preceding Monday or Thursday that is closest to the actual ensemble run date24 year period: Jan 1993 to Dec 2016.
• each re-forecast is from an 25-member ensemble (all perturbed members) run over the 46-day ensemble forecast perioda 7-month forecast period for monthly runs, and a 13-month forecast period for quarterly runs.

In total, each set of re-forecasts consists of

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24 years x

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1 runs x

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25 ensemble members =

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600 re-forecast values.  These are available for each forecast parameter, forecast lead-time,

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month, location, at forecast intervals of 6 hours.  These are used to define the

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S-M-climate.

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A lower number of

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re-forecasts

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Each re-forecast consists of a 25-member ensemble (all members are perturbed) run over a 7-month forecast period for monthly runs, and a 13-month forecast period for quarterly runs.  Therefore altogether 24 years x 25 ENS members = 600 re-forecast values are available for each forecast parameter, forecast lead-time, calendar start date (the 1st of each month) and location.  These are used to define the S-M-climate.  This shorter period of re-forecasts is overall nearer to the current date, for two reasonsis justified:

• to be compatible with other seasonal forecast products provided through the auspices of Copernicus (this is their standard re-forecast period).
• to be more compatible with "current climate" (which is changing primarily due to global warming).

The S-M-climate is used in association with the seasonal ensemble forecast:

• to highlight significant monthly anomalies of forecast parameters (2m temperature, 500 hPa height, 850 hPa temperature, mean sea level pressure, precipitation) from the norm for a given location and time of year.