To help users to improve S2S ECMWF MARS requests performance via the WebAPI.

A good understanding of the MARS efficiency issues is essential especially for users that are interested in downloading large amounts of data.

In general it is organised, as a huge tree, with the indentation below, showing different levels down that tree:

• centre (BoM, ECMWF, NCEP, JMA, ...)
  • realtime or reforecast
    •  type of data (control forecast or perturbed forecast)
      • type of level (single level or pressure level or potential  temperature)
        • model version date (2014-01-01 or ...)
          
          • hindcast dates (2013-09-01, 2013-09-06, 2013-09-11, 2013-09-16,  2013-09-21, 2013-09-26, ...)
            •  time and steps
              • members (for perturbed forecast)
                • levels (for pl or pt)
                  • parameters

The idea is to request as much data as possible from the same tape file. The natural way to group requests would be:
all parameters, all levels, all members, all time-steps for 1 hindcast date for a type of level for a type

Note the following:

1. 'all' means 'all' that the user wants. It doesn't have to be all parameters.
2. If a user is interested only on z500,  he may request more hindcast dates in one go, since the overall request will not be so big.

• The objective of this example is to demonstrate how to iterate efficiently over all the available hincastDates for an ECMWF model version date.
• To start writing your request you firstly need to select a model version date and to find the corresponding Hindcast Dates. Please  check ECMWF availability
  Keep in mind that the ECMWF reforecast configuration is "on the fly". For more information read a brief description of reforecasts.
• The requests below can be used as a starting point, however you need to keep in mind that you have to adapt it to your needs eg to set the keyword values according to your requirements ("param", "levtype", "step" etc).
• In this way you can extend this request to download the whole S2S ECMWF reforecast. Don't forget to check ECMWF availability

You can use the variable target to organise the requested data in files as you wish.

• ECMWF re-forecast requests
• ECMWF Web API Home
• ECMWF re-forecast availability
• A brief description of reforecasts