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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]

Table of Contents

This page is under construction!

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Info
titleThe objective:

In this area we are only focusing on MARS efficiency issues ie to investigate and present what is the most efficient way to loop over several requests for retrieving CMA reforecast data.

How the S2S data is organised in general:

...

The data is organised as a huge tree, with the indentation 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

The natural way to group requests would be:
all parameters, all levels, all members, all time-steps for 1 date.

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 presented above if you need to loop in a MARS request, follow the hierarchy below

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

A more practical example on how to request Control forecast, pressure levels, for years 2010-2014 for month April and June

Info
titleThe main idea in brief:
for each year from 2010 to 2014
    for months April, June
        for each hindcast date
 hindcastDay in list(range(numberOfDays)):
                hindcastDate  API request
= '%04d%02d%02d' % (
Info
titleThe main idea in brief:
for each year from 2010 to 2014    for monthshindcastYear, AprilhindcastMonth, June
hindcastDay + 1)
                target  for each hindcast date
= "%s%s.grb" % (origin, hindcastDate)
                 for each level
cma_reforecast_request(hindcastDate, target)

def cma_reforecast_request(hindcastDate, target):
    """       
     for each parameter
 A CMA reforecast request. Change the keywords

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:

...

below to adapt it to your needs.   
    """
    
    server.retrieve({
        "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",
    })

if __name__ == '__main__':
    retrieve_cma_reforecast()


Useful links

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