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Info

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 ECMWF

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 ECMWF availability and to view an ECMWF 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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Info
  • The objective of this example is to demonstrate how to iterate efficiently over all the available hindcastDays for an ECMWF model version date.

    • To start writing your request you firstly need to know the model version date and the corresponding Hindcast Days you wish to retrieve.
    (lightbulb) Keep in mind that the ECMWF reforecast configuration is "on the fly". For more information read a brief description of reforecasts.


    An ECMWF reforecast request for all the available hindcastDates

    Info
    • The objective of this example is to demonstrate how to iterate efficiently over all the available hindcastDays for an ECMWF model version date.
    • The requests below 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 ECMW Freforecast. Don't forget to check ECMWF availability (warning)

    (smile) You can use the variable target to write the requested data as you wish. In the example below the data is written per leveltype (sfc, pl) per hindcastMonth.

    Code Block
    languagepy
    #!/usr/bin/env python
from ecmwfapi import ECMWFDataServer
server = ECMWFDataServer()

origin = "ecmf"
modelVersionDate = "2015-12-03"
hindcastDates = ["1995-12-03", "1996-12-03", "1997-12-03", "1998-12-03", "1999-12-03", "2000-12-03",
    "2001-12-03", "2002-12-03", "2003-12-03", "2004-12-03", "2005-12-03", "2006-12-03", "2007-12-03", 
    "2008-12-03", "2009-12-03", "2010-12-03", "2011-12-03", "2012-12-03", "2013-12-03", "2014-12-03"]

def retrieve_ECMWF_reforecast():
    """
       A function to demonstrate how to iterate efficiently over all hindcastDays hindcastDates
       for a particular ECMWF reforecast model version.
       Change the variables below to adapt the iteration to your needs
    """
           
    #Please note that the "sfc" and "pl" requests below could run in parallel
           
    #Step 1: Get pressure level data
    pfplTarget = "%s_%s_%_%s.grb" % (origin, "pfpl", modelVersionDate)
    ECMWF_reforecast_pf_pl_request("/".join(hindcastDates), pfplTarget)
           
    #Step 2: Get surface data
    pfsfcTarget = "%s_%s_%s.grb" % (origin, "pfsfc", modelVersionDate)
    ECMWF_reforecast_pf_sfc_request("/".join(hindcastDates), pfsfcTarget)

def ECMWF_reforecast_pf_pl_request(hindcastDate, target):
    """
       A ECMWF reforecast, perturbed forecast, pressure level, request.
       The cost of this request is fields and  Gbytes 
       Change the keywords below to adapt it to your needs.
    """
    server.retrieve({
        "class": "s2",
        "dataset": "s2s",
        "date": modelVersionDate,
        "expver": "prod",
        "hdate": hindcastDates,
        "levtype": "pl",
        "levelist": "10/50/100/200/300/500/700/850/925/1000",
        "origin": origin,
        "param": "130/131/132/133/135/156",
        "step": "24/to/768/by/24",
        "stream": "enfh",
        "target": target,
        "time": "00",
        "number": "1/2/3/4",
        "type": "pf",
    })

def ECMWF_reforecast_pf_sfc_request(hindcastDate, target):
    """
       A ECMWFreforecast, perturbed forecast, sfc request.
       The cost of this request is 383,040 fields and 7.1 GB
       Change the keywords below to adapt it to your needs.
    """
    server.retrieve({
        "class": "s2",
        "dataset": "s2s",
        "date": modelVersionDate,
        "expver": "prod",
        "hdate": hindcastDate,
        "levtype": "sfc",
        "origin": origin,
        "param": "1/33/34/59/121/122/134/136/146/147/151/165/166/167/168/169/175/176/177/179/180/181/235",
        "step": "24/to/744/by/24",
        "stream": "enfh",
        "target": target,
        "time": "00",
        "number": "1/2/3/4",
        "type": "pf",
    })

if __name__ == '__main__':
    retrieve_ECMWF_reforecast()

    ...