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Table of Contents

This page is under construction!

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

Info
titleThe objective:

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

The aim of this page is to help users to improve their MARS requests performance focusing in CMA reforecast MARS requests.

How the S2S data is organised in general?

...

First you need to understand how the S2S data is organised in MARS.

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

  • centre (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)
          • Hdates (2015-01-01 or 2015-01-05 or 2015-01-08, ...)
            •  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)):

...

What would be the natural way to group requests?

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

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

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

Info
titleThe main idea in brief:
for Hdate in Hdate-list
     your-s2S-request(Hdate)

An example to request Control forecast, pressure levels from 2010-03-01 to 2010-03-31

Info
titleThe main idea in brief:
for each Hdate from 2010-03-01 to 2010-03-31
    call your-s2s-request(Hdate)

An example of  "your-API-S2S-request"

Retrieving  1 field (10m U wind) for all time steps

What is the best approach to get all Hdays for several Hyears ?

Info
titleThe main idea in brief:
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.
for Hyear in Hyears 
    for Hmonth in Hyear
        for HdayshindcastMonth in Hmonth
   list(range(hindcastMonthStart, hindcastMonthEnd + 1)):
            HdatenumberOfDays = Hyear-Hmonth-Hday calendar.monthrange(hindcastYear, hindcastMonth)[1]
            for hindcastDay   your-s2S-request(Hdate)

What is the best approach to get all Hdays for several Hyears and Hmonths  and for several hindcasts ?

Info
titleThe main idea in brief:
for Hyear in Hyears 
    for Hmonth in Hyear
        for Hdays in Hmonth
in list(range(numberOfDays)):
                hindcastDate = '%04d%02d%02d' % (
                    hindcastYear, hindcastMonth, hindcastDay + 1)
                Hdatetarget = Hyear-Hmonth-Hday"%s%s.grb" % (origin, hindcastDate)
                your-S2S-cma_reforecast_request(Hdate)

An example to request Control forecast, sfc, for Hyears 2010-2014 for 2 Hmonths  (eg April and June)

Info
titleThe main idea in brief:
for each Hyear from 2010 to 2014
    for Hmonth in April, June
        for Hday in Hmonth
             Hdate = Hyear-Hmonth-Hday
     hindcastDate, target)

def cma_reforecast_request(hindcastDate, target):
    """       
        A CMA reforecast request. Change the keywords below to adapt it to your needs.   
    """
    
    server.retrieve({
        your-S2S-request(Hdate)

old below:

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...

titleThe objective:

...

 

 

 

An example to request Control forecast, pressure levels, for Hyears 2010-2014 for 2 Hmonths (eg April and June)

Info
titleThe main idea in brief:
for each Hyear from 2010 to 2014
    for Hmonths April, June
        for each hindcast Hdate
"class": "s2",
        "dataset": "s2s",
        "date": modelVersionDate,
        "expver": "prod",
        "hdate": hindcastDate,
        "levtype": "sfc",
        "origin": origin,
        "param": "165/166",
        "step": "24/to/1440/by/24",
        "stream": "enfh",
        "target": target,
        "time": "00",
        "number": "1/2/3",
        "type": "pf",
   your-request
         })

if __name__ == '__main__':
    retrieve_cma_reforecast()


Useful links

Info