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changes.mady.by.user Matthew Manoussakis

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Info
titleThe objective:

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

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

How is the S2S reforecast data organised in MARS?

Info

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

  • centre (CMA, 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 (2014-05-01 or ...)
            • hindcast dates (2014-01-01 or 2014-01-02 or 2014-01-03, ...)
              •  time-steps
                • members (for perturbed forecast)
                  • levels (for pl or pt)
                    • parameters

What would be the natural way to group requests?

Info

(lightbulb) The idea is to request as much data as possible from the same tape file, all time-steps, all members, all parameters for a type of level, a type, a hindcast date

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. The natural way to group requests

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Info

Following the previous paragraph,  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

(warning) 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.

Best

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To iterate over several hindcastDates for a CMA request

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titleThe main idea in brief:

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practise to iterate over all hindcastDates of

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several hindcastYears

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for

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CMA

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The main idea in brief:
Info
title

(lightbulb) The best approach is to iterate over the hindcastYears. For each hindcastYear iterate over all the available hindcastMonths and for each hindcastMonth iterate over all the available hindcastDays.

(warning) At this point you may wish to check CMA availability and to view a CMA request

The main idea in brief:
Info
title
for hindcastYear in hindcastYears
    for hindcastMonth in hindcastMonths        
        for hindcastDay in hindcastDays             
            hindcastDate = HindcastYear-hindcastMonth-hindcastDay               
                S2S-request(hindcastDate)

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Code Block
languagepy
#!/usr/bin/env python
from ecmwfapi import ECMWFDataServer
server = ECMWFDataServer()
def retrieve_data(hindcastDate):
    target = "target_s2s_%s.grb" % hindcastDate
    server.retrieve({
       "class": "s2",
       "dataset": "s2s",
       "date": "2014-05-01",
       "expver": "prod",
       "hdate": hindcastDate,
       "levtype": "sfc",
       "origin": "babj",
       "param": "165",
       "step": "0",
       "stream": "enfh",
       "target": target,
       "time": "00",
       "type": "cf",
})

for hindcastYear in ["2012", "2013"]:
    for hindcastMonth in ["08", "09"]:
        for hindcastDay in ["01", "02"]:
            hindcastDate = hindcastYear+hindcastMonth+hindcastDay
            retrieve_data(hindcastDate)

Useful links