Page History

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• There is no clear-cut distinction here on what is a forecast and what a hindcast, and from the point of view of RD having a distinction can be an unnecessary complication.
• However there might be some merit in doing the distinction for users' benefit:
  • Using different MARS streams (as for medium-range, extended-range) is seen as unnecessary here
  • The use of typeOfGeneratingProcess=15 (Hindcast) from Section 4, cod code table 3 was seen as appropriate
  • The distinction between section 4 templates 1,11 and 60,61 (the latter only add modelVersionDate) was considered not strictly needed

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• The use of MARS method (to distinguish 7-month runs from 13-month runs) is not a requirement, but it was introduced in the past to avoid significant performance degradation in MARS
  • Without "method" we would have some very sparse data hypercubes (the "annual" runs produce much fewer variables and members and it also has longer but less frequent steps). 
    • Note that future ECMWF system designs can be even more complicated than the current one (currently 12 start dates "7month-long", 4 start dates "13month-long")
  • A distinction between those different forecast ranges can be, though, useful for users

• There is a strong felling that we would need to have GRIB keywords to encode the following elements: "system", "method" (this one could be called "range" or something similar)
  
  • A potential way forward was seen in having a section 4 template including those elements for both forecasts and hindcasts.
    • Keeping in that template modelVersionDate would help to properly label the ensemble member numbers for systems producing hindcasts on-the-fly which could need to cycle (produce the same members/start dates in different "production" years)

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