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

Info
  • The

Table of Contents

 

What is the objective of this page?

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 MARS?

...

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)
          • model version date (2014-05-01 or ...)
            • hindcast dates (2014-01-01 or 2014-01-02 or 2014-01-03, ...)
              •  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 hindcast 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 hindcast dates 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?

...

titleThe main idea in brief:

...

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

Info
titleThe main idea in brief:
(lightbulb) The
  • best approach is to iterate over the
HindcastYears
  • hindcastYears.
  • For each
HindcastYear
  • hindcastYear iterate over all the available hindcastMonths and for each hindcastMonth iterate over all the available hindcastDays.

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

Info
titleThe main idea in brief:
for HindcastYearhindcastYear in HindcastYearshindcastYears
    for hindcastMonth in hindcastMonths        
        for hindcastDay in hindcastDays             
            hindcastDate = HindcastYearhindcastYear-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"
hindcastDate = "2014-04-01"  # The selected hindcast date
server = ECMWFDataServer()
server.retrieve({
    "class": "s2",
    "dataset": "s2s",
    "date": ModelVersionDate,
    "expver": "prod",
    "hdate": hindcastDate, 
    "levtype": "sfc",
    "origin": "babj",
    "param": "165",
    "step": "0",
    "stream": "enfh",
    "target": "data.cf.sfc",
    "time": "00",
    "type": "cf",
})
Info

(lightbulb) If the request is "small" you may request more hindcastDates in one go. See the example below.

A web API example requesting data for several hindcastDates (iterating over several hindcastYears, hindcastMonths and hindcastDays)

  • The objective of this example is to demonstrate how to make a MARS request efficient by iterating properly. 
    • It can be used as a starting point however you need to adapt it to your needseg:
    • to set the keyword values (eg hindcastYear)  according to your needs. 
    • don't forget to check CMA availability (warning)
    • to make it more "pythonic" (wink)

    (grey lightbulb) By setting the variable "target" accordingly you can have each hindcastDate to be written on a separate file .

    Info
    Code Block
    languagepy
    #!/usr/bin/env python
from ecmwfapi import ECMWFDataServer
server = ECMWFDataServer()
def retrieve_data(hindcastDate):
    target = "target_s2s_%s.grb" % hindcastDate

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):
    """       
        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": hindcastDate,
        "levtype": "sfc",
        "origin": "babj"origin,
        "param": "165/166",
        "step": "024/to/1440/by/24",
        "stream": "enfh",
        "target": target,
        "time": "00",
        "typenumber": "cf1/2/3",
})

for hindcastYear in ["2012", "2013"]:
    for hindcastMonth in ["08", "09"]:
        for hindcastDay in ["01", "02"]:type": "pf",
    })

if        hindcastDate = hindcastYear+hindcastMonth+hindcastDay
        __name__ == '__main__':
    retrieve_cma_datareforecast(hindcastDate))


    Useful links

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