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tThe The following MARS requests can be used as a tutorial. The links into the MARS Catalogue might be helpful to create a valid retrieve script. However, the dates might need to be adapted.

...

retrieve,
    class    = od,
    type     = an, 
    expver   = 1,
    date     = 19990215,
    time     = 12,
    param    = t130.128, 
    levtype  = pressure level,
    levelist = 1000/850/700/500,
    target   = "t.grb"

Retrieve wind components valid for tomorrow 5 days ago at 12:00 and 18:00 from yesterday's 12Z forecast at forecast made 7 days ago at 12 UTC at all 137 model levels  > see in MARS Catalogue

retrieve,
    type     = forecast, 
    param    = u131/v132, 
    levtype  = model level,
    levelist = 1/to/137,
    date     = -17,
    time     = 12,
    step     = 48/54, 
    target   = "wind"

Retrieve geopotential and surface pressure for yesterday's from analysis produced 2 days ago, analysis cycles (00,06,12,18)  > see in MARS Catalogue

retrieve,
    class   = od,
    type    = analysis,
    levtype = surface,
    date    = -12,
    time    = 00/06/12/18,
    param   = z/sp129.128/134.128,
    target  = "all.an"

Retrieve surface pressure and surface long-wave (thermal) radiation downwards at every 12-hour time-step for the 12Z forecast from two 12 days ago  > see in MARS Catalogue

retrieve,
    type    = forecast,
    param   = sp/str134.128/175.128,
    date    = -212,
    step    = 12/to/240/by/12,
    time    = 12,
    levtype = sfc,
    target  = "sfc.grb"

...

retrieve,
    class    = od,
    stream   = mnth,
    type     = analysis,
    time     = 06,
    date     = 19970200,
    levtype  = model level,
    param    = t130.128,
    levelist = 1/to/31137, 
    target   = "monthly"

Retrieve the temperature on model levels 1, 2 and 3 for yesterday's a week old 12 hour forecast.   > see in MARS Catalogue

retrieve,
    type    = fc,
    date    = -17,
    time    = 12,
    step    = 12,
    levtype = ml,
    level   = 1/2/3,
    param   = t130,
    target  = "t_ml_1_2_3"

Time and step

Retrieve the 1000 hPa geopotential from yesterday's two weeks old 12 UTC forecast (> see in MARS Catalogue) for:

• the 12 hour forecast

  Expand
  title solution
  retrieve, type = fc, date = -114, time = 12, step = 12, levtype = pl, level = 1000, param = z129.128, target = "z1000_a"

  
  

• the 6, 12, 24 and 48 hour forecasts

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  title solution
  retrieve, type = fc, date = -114, time = 12, step = 6/12/24/48, levtype = pl, level = 1000, param = z129.128, target = "z1000_b"

  
  

• the 12 hour to 240 hour forecasts at 12 hour intervals

  Expand
  title solution
  retrieve, type = fc, date = -114, time = 12, step = 12/to/240/by/12, levtype = pl, level = 1000, param = z129.128, target = "z1000_c"

  
  

• all forecast time-steps (tip: you can use MARS catalogue to generate list of all available steps for you)

  Expand
  title solution
  retrieve, type = fc, date = -1, time = 12, # step = all, # The value "all" is convenient to use but MARS can only report on missing steps if # the full list of steps is specified: step = 0/1/2/3/4/5/6/7/8/9/10/11/12/13/14/15/16/17/18/19/20/21/22/23/24/25/26/27/28/29/30/31/32/33/34/35/36/37/38/39/40/41/42/43/44/45/46/47/48/49/50/51/52/53/54/55/56/57/58/59/60/61/62/63/64/65/66/67/68/69/70/71/72/73/74/75/76/77/78/79/80/81/82/83/84/85/86/87/88/89/90/93/96/99/102/105/108/111/114/117/120/123/126/129/132/135/138/141/144/150/156/162/168/174/180/186/192/198/204/210/216/222/228/234/240, levtype = pl, level = 1000, param = z129.128, target = "z1000_d"

  
  

ENS Overlap

Retrieve Total Precipitation, perturbed forecast overlap for 26th June 2023 (> see in MARS Catalogue)

retrieve,

    class = od,
    date = 2023-06-26,
    expver = 1,
    levtype = sfc,
    number = 1/to/50,
    param = 228.128,
    step = 336,
    stream = efov,
    time = 00:00:00,
    type = pf,
    target = [stream]_[date].grb

See also FAQ: "How can I compute the accumulation using data from the overlap stream?"

Post-processing

Retrieve the 1000,500 and 300 hPa temperatures valid for today day before yesterday at noon from the 12 UTC forecast of two four days ago on an N48 Gaussian Grid  > see in MARS Catalogue

retrieve, 
    class    = od,
    stream   = oper,
    expver   = 1,
    type     = forecast, 
    param    = t130.128, 
    date     = -24,
    time     = 12, 
    step     = 48, 
    grid     = N48, 
    levelist = 1000/500/300, 
    levtype  = pl, 
    target   = "t.gg.grb"

Retrieve the same on a latitude/longitude grid, 1.5 by 1.5 degrees. > see in MARS Catalogue

retrieve,
 
     class type     = forecastod,

    param  stream  = toper,

    date    expver = -21,
 
   time    type = 12forecast,

      levelistparam = 1000/500/300,
130.128,
     levtype date = pl,
-4,
      steptime = 12,
      step = 48,

    grid   grid  = 1.5/1.5,

    target  levelist = "t1000/500/300,
      levtype = pl,
      target   = "t.ll.grb"

Retrieve Europe in the same way as in the previous retrieval. Compare the size of the resulting file with the previous one. > see in MARS Catalogue

retrieve,

    class = typeod,
    stream = fcoper,

    paramexpver    = t1,
 
   date type    = -2forecast,

    timeparam     = 12,
= 130.128,
    levelistdate = 1000/500/300,
-4,
    levtypetime  = pl12,

    step     = 48,

    grid     = 1.5/1.5,
   ,
    levelist = 1000/500/300,
    levtype = pl, 
    area     = e,
    target   = "t.europe"

Retrieve the 1000 and 500 hPa geopotential for 1200 yesterday from the analysis UTC analysis from two days ago in the formats below (one job for each form): > see in MARS Catalogue

• leaving the data in its original form

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  title solution
  retrieve, type class = anod, date = -12, timeexpver = 121, paramlevelist = z500/1000, levtype = pressure level, level param = 1000/500129.128, targetstream = "myfile1"

  reducing the truncation to T106

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  title solution
  retrieveoper, typetime = 12, type= an,   date target = "myfile_d"

  
  

• reducing the truncation to T106

  Expand
  title solution
  retrieve, class = od, -1, time date = 12-2, paramexpver = 1, levelist = z, 500/1000, levtype = pressure level, levelparam = 129.128, stream = 1000/500, oper, time = 12, resoltype=an,    truncation = 106, target = "myfile1myfile_106"

  
  

• converting the data to a global N48 Gaussian grid

  Expand
  title solution
  retrieve, typeclass = anod, date = -12, paramexpver = z1, levelist = 500/1000, levtype = pressure level, level = 1000/500, grid param = 129.128, stream = oper, time = 12, type=an, grid = N48, target = "myfile1myfile_N48"

  
  

• converting the data to a regular 5.0 by 5.0 degree global latitude/longitude grid

  Expand
  title solution
  retrieve, typeclass = anod, date = -2, expver = -1, paramlevelist = z500/1000, levtype = pressure level, param = 129.128, level stream = 1000/500, oper, time = grid12, = 5.0/5.0, type=an, target grid = "myfile1"0.5/0.5, target = "myfile_ll"

  
  

• converting the data to an N80 Gaussian grid for the European area

  Expand
  title solution
  retrieve, type class = an, od, date = -2, expver = -1, param = z, levelist = 500/1000, levtype = pressure level, param = 129.128, stream = leveloper, time = = 1000/500, grid 12, type=an, grid = N80, area = europe, target = "myfile1myfile_N80"

  
  

• converting the data to an N80 Gaussian grid for the area from 50 degrees North to 10 degrees North, and 20 degrees West to 20 degrees East

  Expand
  title solution
  retrieve, typeclass = anod, date = -2, expver = -1, paramlevelist = z500/1000, levtype = pressure level, param = 129.128, level stream = 1000/500, gridoper, time = 12, type = N80an, areagrid = N80, area = 50/-20/10/20, target = "myfile1myfile_N80_reg"

  
  

• converting the data to the same area but convert it to a 2.5 degree by 2.5 degree latitude/longitude grid

  Expand
  title solution
  retrieve, typeclass = od, = an, date = -2, date expver = -1, param levelist = z, 500/1000, levtype = pressure level, level param = 1000/500, 129.128, gridstream = 2.5/2.5, oper, areatime = 12, type = an, grid = 0.25/0.25, area = 50/-20/10/20, target = "myfile1myfile_ll_reg"

  
  

Retrieve surface winds for yesterdayprevious week's 24 hour forecast on the European area converting to a 0.57 by 0.57 degrees latitude/longitude grid. > see in MARS Catalogue
What happens to the conversion?

retrieve,
    type    = fcclass=od,
    date=-7,
    expver= -1,
    timelevtype=sfc,
    = 12,
    step    = 24,
    levtype = sfc,
    param   = 10u/10v=165.128/166.128,
    area    = europe,       # As the area is not compatible with the grid,
    grid    = 0.57/0.57,    # MARS will expand the area to make it fit.
    target  = "10u_10v"

Observations

Retrieve all the sea surface observations for the 1st February 2015.  > see in MARS Catalogue

retrieve, 
    type    = ob, 
    obsgroup= con,
    obstype = ssd,
    date    = 20150201, 
    time    = 00,
    range   = 1439,
    target  = "obs.bufr"

Ensemble forecasts

step=24,
    stream=oper,
    time=12:00:00,
    type=fc,    
    area = europe,         # As the area is not compatible with the grid, 
    grid = 0.57/0.57,      # MARS will expand the area to make it fit.
    target = "10u_10v"

Observations

Retrieve all the sea surface observations for the 1st February 2015.  Retrieve the surface temperature fields of the first 10 members of yesterday's 12 UTC ensemble prediction (type: perturbed forecast) for the next 3 days at noon. > see in MARS Catalogue

retrieve, 
    type    = classob, 
    obsgroup= odcon,
    obstype = ssd,
#   obstype = 9/11/12/13/14/19/21/22/23/180/181/182,

    date stream   = ef20150201, 
    type time    = perturbed forecast00,
    levtyperange   = sfc1439,
    represtarget  = "obs.bufr"

Ensemble forecasts

Retrieve the 2 metre temperature field of the first 10 members of a week old 12 UTC ensemble prediction (type: perturbed forecast) for 2, 3 and 4 days in advance > see in MARS Catalogue

retrieve,
 = gg,
    dateclass=od,
     date= -17,

    timeexpver=1,
     levtype= 12sfc,

    ensemble number= 1/to/10,

    stepparam=167.128,
     step= 48/to/96/by/24,

    stream=enfo,
    param time=12,
    type=pf,
   = st, target = "ensemble"

Retrieve the same for the control forecast. > see in MARS Catalogue

retrieve,

    class   = od,

    stream  = ef,
date=-7,
    type    = control forecast,
    levtype = sfc,
    repres  = gg,
    date    = -1,
expver=1,
    timelevtype=sfc,
    param= 12,
167.128,
    step    = 48/to/96/by/24,

    paramstream=enfo,
    time= st,
12,
    type=cf,
    target  = "ensemble.cf"

ERA

...

5

Retrieve the vertical integral of eastward and northward heat flux as monthly means of daily means on a 1.125 by 1.125 degree latitude/longitude grid over Europe from the ERA 40 5 archive for January 1964 2021 > see in MARS Catalogue

retrieve,
    class   = e4ea,
    streamdate  = moda20210101,
    typedecade    = an2020,
    levtypeexpver = sfc1,
    datelevtype    = 19640101sfc,
    param   = 69.162/70.162,
    stream area= moda,
    type = european,

    area = grideurope,
    grid = 1.125/1.125,
 
    target  = "e4ea_moda_fluxes.grb"

Retrieval of snow depth from the ERA -40 5 archive for November 1993, for all analysis base times > see in MARS Catalogue. How many fields are requested?

retrieve,
  class   = e4ea,
  stream  = oper,
  expver  = 1,
  date    = 19931101/to/19931130,
  time    = 00/06to/12/1823,
  type    = an,
  levtype = sfc, 
  param   = sd141.128,
  repres  = gg,
  target  = "era40era5.199311.sd"

#                                  It retrieves 30 x 424 = 120720 fields.

See also these Web API retrieve examples for ERA-Interim, S2S, TIGGE, ERA-20C etc.