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Table of Contents

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Best practise to iterate over all hindcastDates of several hindcastYears for CMA

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 the S2S data is organised in general in MARS?

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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)
          • HindcastDates (2014-01-01 or 2014-01-02 or 2014-01-03, ...)
            •  time-steps
              • members (for perturbed forecast)
                • levels (for pl or pt)
                  • parameters
  • 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.

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

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

Web-API examples:

A CMA 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 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 reforecast.

Please note:

  • you can set the variable "target"  to write each hindcastDate on a separate file (lightbulb)
  • 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()

origin = "babj"
modelVersionDate = "2014-05-01"

def retrieve_cma_reforecast():
    """       
       A function to demonstrate how to iterate efficiently over all hindcastYears, hindcastMonths etc     
       for a particular cma_reforecast_request.      
       Change the variables below to adapt the iteration to your needs 
    """
    hindcastYearStart = 1994
    hindcastYearEnd = 2014
    hindcastMonthStart = 1
    hindcastMonthEnd = 12
    
    for hindcastYear in list(range(hindcastYearStart, hindcastYearEnd + 1)):
        for hindcastMonth in list(range(hindcastMonthStart, hindcastMonthEnd + 1)):
            numberOfDays = calendar.monthrange(hindcastYear, hindcastMonth)[1]

...

What would be the natural way to group requests?

Info

Following the previous paragraph,  the natural way to group requests would be:
all parameters, all levels, all members, all time-steps for 1 HindcastDate.

(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 HindcastDates in one go, since the overall request will not be so big.

 What is the best approach to loop over several HindcastDates  for a CMA request?

Info
titleThe main idea in brief:
for HindcastDate in HindcastDate-list (eg, 2010-03-01 to 2010-03-31)
     S2S-request(HindcastDate)

What is the best approach to get all HindcastDays for several HindcastYears ?

The best approach is to iterate over the Hyears you wish. For each Hyear iterate over all Hmonths and for each Hmonth iterate over all its Hdays.

Info
titleThe main idea in brief:
for HindcastYear in HindcastYears 
    for HindcastMonth in HindcastYear
        for HindcastDay in HindcastMonth
             HindcastDate = HindcastYear-HindcastMonth-HindcastDays
                 S2S-request(HindcastDate)

An example to request Control forecast, single level, for HindcastYears 2010 to 2014 for 2 HindcastMonths  (eg April and June)

Info
titleThe main idea in brief:
for each HindcastYear from 2010 to 2014
    for HindcastMonth in 04, 06
        for HindcastDay in HindcastMonthhindcastDay in list(range(numberOfDays)):
                hindcastDate = '%04d%02d%02d' % (
                    hindcastYear, hindcastMonth, hindcastDay + 1)
                HindcastDatetarget = HindcastYear-HindcastMonth-HindcastDay "%s%s.grb" % (origin, hindcastDate)
                S2S-cma_reforecast_request(HindcastDate) (see below an example)

An S2S-request example

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

def cma_reforecast_request(hindcastDate, target):
    """       
        A CMA reforecast request. Change the keywords below to adapt it to your needs.   
    """
    
    server.retrieve({
        "class": "s2",
        "dataset": "s2s",
        "date": "2014-05-01"modelVersionDate,
        "expver": "prod",
        "hdate": HindcastDatehindcastDate,
 (ie the selected HindcastDate eg "2006-06-08"),
    "levtype": "sfc",
        "origin": "babj"origin,
        "param": "165/166",
        "step": "024/to/1440/by/24",
        "stream": "enfh",
        "target": target,
        "time": "CHANGEME00",
        "timenumber": "001/2/3",
        "type": "cfpf",
    })

 

)

if __name__ == '__main__':
    retrieve_cma_reforecast()


Useful links

Info

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