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Comment: Confirmed.

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

Info
  • 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]
            for hindcastDay in list(range(numberOfDays)):
                hindcastDate = '%04d%02d%02d' % (
                    hindcastYear, hindcastMonth, hindcastDay + 1)
                target = "%s%s.grb" % (origin, hindcastDate)
                cma_reforecast_request(hindcastDate, target)

def cma_reforecast_request(hindcastDate, target):
    """       

Table of Contents

This page is under construction!

...

Info
titleThe objective:

A good understanding of the MARS efficiency issues is essential especially for downloading large amounts of data.

The aim of this page is to help users to improve their MARS requests performance focusing in CMA reforecast data using the ECMWF WEB API.

How the S2S data is organised in general?

...

It is every important for a user to understand how the S2S data is organised in MARS.

In general it is organised in MARS 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)
          • dates (2015-01-01 or 2015-01-05 or 2015-01-08, ...)
            •  time-steps
              • members (for perturbed forecast)
                • levels (for pl or pt)
                  • parameters

...

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 date.

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

What is the most efficient way to loop over several CMA requests?

Info
titleThe main idea in brief:

Taking under consideration what has been explained above,  if you need to loop in a MARS request, follow the hierarchy below

  • date
    • hindcast date
      • number (EPS only)
        • level
          • parameter (inner loop)

 A pseudo algorithm to loop over several dates for a CMA request?

Info
titleThe main idea in brief:
  • for date in dates-list
    • for hindcast date in hincasts-list
            request

A pseudo algorithm on how to request Control forecast, pressure levels, for years 2010-2014 for 2 months (eg April and June)

Info
titleThe main idea in brief:
for each year from 2010 to 2014
    for months April, June
for each hindcast date
A CMA request
reforecast request. Change the keywords below to adapt it to your needs. """   server.retrieve({ "class": "s2",
Info
titleThe main idea in brief:
"dataset": "s2s",
        

old below:

---------------

Info
titleThe main idea in brief:
  1.  4 categories of requests:
    1. control plevels
    2. control sfc
    3. ensemble plevels
    4. ensemble sfc
  2. For each category above:
    1. For each year from 1994 to 2014
      1. For each month from January to December
        1. retrieve hindcast dates 1-15 using requests according to data availability*
          1. API request 1
          2. API request 2
          3. API request 3
        2. retrieve hindcast dates 15-end of month using requests according to data availability
          1. API request 1
          2. API request 2
          3. API request 3
  • for instance
    • for plevels different parameters are available on different levels so Ben has created 3 pl requests
    • for sfc different parameters are available for different  steps so he has created 3 sfc requests

...

titleThe objective:

...

"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",
    })

if __name__ == '__main__':
    retrieve_cma_reforecast()


Useful links

Info

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