Identify the data you want

• ML, 3 parameters
• Time: 00 and 12, April 2017
• first 90 steps, every hour (0/to/90/by/1)
• 10 levels closer to surface (127/to/137)

Use MARS list to find out the size

LIST,
    OUTPUT     = COST,
    CLASS      = OD,
    TYPE       = FC,
    STREAM     = OPER,
    EXPVER     = 0001,
    LEVTYPE    = ML,
    LEVELIST   = 127/128/129/130/131/132/133/134/135/136/137,
    PARAM      = 130/131/132,
    DATE       = 20170401/20170402/20170403/20170404/20170405/20170406/20170407/20170408/20170409/20170410/20170411/20170412/20170413/20170414/20170415/20170416/20170417/20170418/20170419/20170420/20170421/20170422/20170423/20170424/20170425/20170426/20170427/20170428/20170429/20170430,
    TIME       = 0000/1200,
    STEP       = 0/to/90/by/1,
    TARGET     = list.txt

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Use the MARS catalogue to know the data distribution in files and tapes

Using the MARS catalogue we browse the data we want to get until we get to the final stage which gives us a selection and several options: http://apps.ecmwf.int/mars-catalogue/?class=od&stream=oper&expver=1&type=fc&year=2017&month=apr&levtype=ml&date=2017-04-01&time=00:00:00

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Now that we know the size of the data that we want to retrive in one go from the same hypercube we can start the study of the way to iterate to get the full time and date.

Split the request in sensible chunks iterating through the correct keywords

Using the browser we know how the data is distributed in the MARS tree. Now we focus on the current selection section. In this case:

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