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• Read here general information how to access efficiently data from MARS via Web API and thus to improve you MARS retrieval performance dramatically.
• Visit the MARS Retrieval efficiency pages for even more information.

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

1) Deterministic data (stream oper):

• origin and model
  
  • type of data (analysis, forecast, etc)
    • year
      
      • month
        • type of level (model level, pressure level, surface etc) 
          • dates, times, steps (for forecast type), levels (for non surface levels), parameters

2) Ensemble data (stream enda):

• origin and model
  • type of data (analysis, forecast, etc)year
    • month
      • type of level (model level, pressure level, surface etc) 
        
        •  dates
          • times, steps (for forecast type), levels (for non surface levels), parameters, members (for ensembles)

The items on the lowest level in the trees above are archived on the same tape. The tree structure can be easily understood by investigating  the deepest UERRA Web MARS page (where one can select exactly which parameters are neededuser login is required to access this page). All selectable items listed in the web listboxes on that page represent data occupying the same archiving tape.

The idea is to request as much data as possible from the same tape file (all selectable items listed in the web listboxes; user login is required to access this page)  

 The natural way to group requests would be for example for the deterministic data:
all dates, times, steps, levels and parameters of a given month

Note: 'all' means 'all' that the user wants. It doesn't have to be all parameters.