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All data retrievals should be submitted as as (ecgate) batch jobs .

MARS can be called with the command line options listed in the table below. Most of these options are particularly useful when problems arise.

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• Leading spaces and tab characters are ignored.
• verbs and directives keyword=value have to be terminated with a comma, except the last one, which MARS considers as the end of a request.
• Directives may be in upper or lower case or a mixture of both; MARS converts everything except filenames file names to upper case.
• Characters * ! and # can be used to comment until end-of-line.
• Values may be predefined names, numeric values or user-supplied character strings such as filenamesfile names.
• Abbreviations may be used for verbs, keywords and values, provided enough letters are given to uniquely identify what is meant.
• MARS has acronyms for the names of different parameters which can be specified by users.
• Keywords may be assigned a single value, a list of values or a range of values. A list is indicated by the separator / ; a range is indicated by using the keywords to as well as / and by. Examples of different formats for values are given in the table below.

  Examples of MARS keyword assignments
  Format	Example
  single value	param = temperature/SSRD
  list of values	step = 12/24/48
  range of values	date = 19990104/to/19990110/by/2

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retrieve                                                        action
  class=od
  stream   = oper,                                  identification of archive
  expver   = 1,
  date     = -1,                                      date and time related
  type     = analysis,
  levtype  = model levels,
  levelist = 1/to/91,
  param    = temperature,
  grid     = 2.5/2.5,                           post-processing
  area     = europe,
  use      = infrequent,                    execution control
  target   = analysis.12                    storage

Retrieve requests have to specify, at least, directives to identify the data and directives for storage of the retrieved data. The ones to identify fields can be found in the Archive Catalogue. Data manipulation (post-processing) directives and execution control directives are optional, depending on user's your needs.

With the main focus on data retrievals, this User Guide covers the following MARS actions, or verbs:

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Note that fieldsets are in fact using temporary disk storage on the host where MARS is executed, usually in $TMPDIR directory. When dealing with big fieldsets, users you are advised to make such variable point to a suitable directory were temporary data can be stored (e.g. $SCRATCH on ecgate).

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MARS can accept more than one request in the same invocation. This allows users you e.g. to do further computations than the ones provided by the standard post-processing directives before writing the data into a target file and it is how the compute verb can be used. The following concepts have to be taken into account:

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It is possible to store data from different requests into the same target file. Note that MARS will append the result of each retrieve request at the end of the target file. The following example retrieves first some Analysis data from yesterday. Then, a second retrieval will extract the same data for from 40 days ago run and append it at the end of the (same) target file.

retrieve,
   class  = od,
   type   = analysis,
   stream = oper,
   expver = 1,
   date   = -1,
   time   = 12,
   levtype= pressure levels,
   levelis= 1000/850/500,
   param  = temperature,
   target = "analysis.grb"
retrieve,
   date   = -40,
   target = "analysis.grb"     

Manipulate already retrieved data

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The advantage of retrieve is that it will fail if the requested data is not present in the source file. A disadvantage is that it the request has to specify all the directives, and the user you might not know what are is the exact contents of the source file.