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Info

To help users to improve S2S CMA BoM 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.

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

  • centre (CMABoM, 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

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The idea is to request as much data as possible from the same tape file. 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 practise to iterate over all hindcastDates of several hindcastYears for

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BoM

Info

(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 BoM availability and to view a CMA BoM request

Info
for hindcastYear in hindcastYears
    for hindcastMonth in hindcastMonths        
        for hindcastDay in hindcastDays             
            hindcastDate = HindcastYear-hindcastMonth-hindcastDay               
                S2S-request(hindcastDate)

Web-API examples:

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BoM reforecast request for one hindcastDate

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The request below is for all members of the perturbed forecast, 10 meter U and V wind components, for all time-steps and for model version 2014-05-01

Code Block
languagepy
#!/usr/bin/env python
from ecmwfapi import ECMWFDataServer

modelVersionDate = "2014-05-01"  # This is the first model version for CMABoM (babj)
hindcastDate = "2014-04-01"      # The selected hindcast date
server = ECMWFDataServer()

server.retrieve({
    "class": "s2",
    "dataset": "s2s",
    "date": modelVersionDate,
    "expver": "prod",
    "hdate": hindcastDate, 
    "levtype": "sfc",
    "origin": "babj",
    "param": "165/166",
    "step": "24/to/1440/by/24",
    "stream": "enfh",
    "target": "data.pf.sfc",
    "time": "00",
    "number": "1/2/3",
    "type": "pf",
})

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BoM reforecast request for all the available hindcastDates

Info
  • The objective of this example is to demonstrate how to iterate efficiently over all the available hindcastYears, hindcastMonths and hindcastDays for a CMA BoM reforecast request
  • It can be used as a starting point, however you need to keep in mind that you have to adapt it to your needseg to set the keyword values according to your requirements ("param", "levtype", "step" etc).
  • In this way you can extend this request to download the whole S2S CMA BoM reforecast. Don't forget to check CMA BoM availability (warning)

(warning) Please note:

  • set the variable "target"  to write each hindcastDate on a separate file .
  • taking under consideration your request's size (eg nr of fields and volume)  you can merge several hindcastDates on the same "target" (smile)
Code Block
languagepy
#!/usr/bin/env python
import calendar
from ecmwfapi import ECMWFDataServer
server = ECMWFDataServer()

hindcastYearStart = 1994
hindcastYearEnd = 2014
hindcastMonthStart = 1
hindcastMonthEnd = 12

def retrieve_cmaBoM_reforecast():
    for hindcastYear in list(range(hindcastYearStart, hindcastYearEnd + 1)):
        for hindcastMonth in list(range(hindcastMonthStart, hindcastMonthEnd + 1)):
            numberOfDays = calendar.monthrange(hindcastYear, hindcastMonth)[1]
            for hindcastDay in list(range(numberOfDays)):
                hindcastDate = '%04d%02d%02d' % (
                    hindcastYear, hindcastMonth, hindcastDay + 1)
                cmaBoM_reforecast_request(hindcastDate)

def cmaBoM_reforecast_request(hindcastDate):
    modelVersionDate = "2014-05-01"
    target = "data_s2s_%s.grb" % (hindcastDate)
    server.retrieve({
        "class": "s2",
        "dataset": "s2s",
        "date": modelVersionDate,
        "expver": "prod",
        "hdate": hindcastDate,
        "levtype": "sfc",
        "origin": "babj",
        "param": "165/166",
        "step": "24/to/1440/by/24",
        "stream": "enfh",
        "target": target,
        "time": "00",
        "number": "1/2/3",
        "type": "pf",
    })

if __name__ == '__main__':
    retrieve_cmaBoM_reforecast()


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