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

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 BoM availability and to view a BoM 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 BoM 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 BoM 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 BoM reforecast.

(warning) Please note:

  • the most efficient way is to request all hindcastDates of a hindcastMonth, in one request, like the example below.
  • you can use the variable target to write the requested data as you wish. In the example below the data is written per leveltype (sfc, pl) per hindcastMonth.
Code Block
languagepy
#!/usr/bin/env python
from ecmwfapi import ECMWFDataServer
server = ECMWFDataServer()

origin = "ammc"
modelVersionDate = "2014-01-01"

def retrieve_BoM_reforecast():
    """
       A function to demonstrate how to iterate efficiently over all hindcastYears, hindcastMonths etc
       for a particular BoM_reforecast_request.
       Change the variables below to adapt the iteration to your needs
    """
    hindcastYearStart = 1981
    hindcastYearEnd = 2013
    hindcastMonthStart = 1
    hindcastMonthEnd = 12
    # BoM availability is every 5 days: 1, 6, 11, 16, 21, 26
    hindcastDays = [1, 6, 11, 16, 21, 26]

    #Step 1: Iterate over all the available hindcastYear(s)
    for hindcastYear in list(range(hindcastYearStart, hindcastYearEnd + 1)):
        #Step 2: Iterate over all the available hindcastMonths(s)       
        for hindcastMonth in list(range(hindcastMonthStart, hindcastMonthEnd + 1)):
            hindcastDates = []
            #Step 3: Create the list of the available hindcastDates

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Table of Contents

 

***************  This page is under construction!    *****************

 

What is the objective of this page?

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titleThe objective:

To help users to improve S2S BoM 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 (BoM)
    • realtime or reforecast
      •  type of data (control forecast or perturbed forecast)
        • type of level (single level or pressure level or potential  temperature)
          • HindcastDates (2013-01-01 or 2013-01-02 or 2013-01-03, ...)
            •  time-steps
              • members (for perturbed forecast)
                • levels (for pl )
                  • parameters

...

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 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 BoM request?

...

titleThe main idea in brief:

...

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 HindcastDayhindcastDay in HindcastMonthhindcastDays:
             
   hindcastDate = '%04d%02d%02d' % (
     HindcastDate = HindcastYear-HindcastMonth-HindcastDays             hindcastYear, hindcastMonth, 
hindcastDay)
                S2S-request(HindcastDate)

An example to request Perturbed forecast, pl, for HindcastYears 2012 to 2013 for 2 HindcastMonths  (eg August & September)

Info
titleThe main idea in brief:
for HindcastYear from 2012 to 2013   
    for HindcastMonth in 08, 09hindcastDates.append(hindcastDate)
           
            #Please note: the steps 4 and 5 below could run in parallel
           
            #Step 4: Get all the available perturbed forecast, pressure level data
            pfplTarget = "%s_%s_%04d%02d.grb" % (
                origin, "pfpl", hindcastYear, hindcastMonth)
            BoM_reforecast_pf_pl_request("/".join(hindcastDates), pfplTarget)
        
   
     for HindcastDay in HindcastMonth    #Step 5: Get all the available perturbed forecast, surface 
data
            HindcastDatepfsfcTarget = HindcastYear-HindcastMonth-HindcastDay "%s_%s_%04d%02d.grb" % (
               
 origin, "pfsfc", hindcastYear, hindcastMonth)
            S2S-request(HindcastDate) (see below an example)

A Perturbed forecast, pl, S2S-request example

Code Block
languagepy
#!/usr/bin/env python
from ecmwfapi import ECMWFDataServer
server = ECMWFDataServer()
BoM_reforecast_pf_sfc_request("/".join(hindcastDates), pfsfcTarget)

def BoM_reforecast_pf_pl_request(hindcastDate, target):
    """
       A BoM reforecast, perturbed forecast, pressure level, request.
       The cost of this request is 571,392 fields and 11.1352 Gbytes 
       Change the keywords below to adapt it to your needs.
    """
    server.retrieve({
        "class": "s2",
        "dataset": "s2s",
        "date": "2014-01-01"modelVersionDate,
        "expver": "prod",
        "hdate": HindcastDatehindcastDate,
 (ie    the selected HindcastDate eg"levtype": "2013-09-01pl"),
        "levelist": "10/50/100/200/300/500/700/850/925/1000",
        "origin": origin,
     "levtype     "param": "130/131/132/133/135/156",
        "step": "pl24/to/1488/by/24",
        "originstream": "enfh",
        "ammctarget": target,
        "paramtime": "133/15600",
        "stepnumber": "24/48
1/to/32",
        "number": "1/2/3/4/5/"type": "pf",
    })

def BoM_reforecast_pf_sfc_request(hindcastDate, target):
    """
       A BoM reforecast, perturbed forecast, sfc request.
       The cost of this request is 383,040 fields and 7.1 GB
       Change the keywords below to adapt it to your needs.
    """
    server.retrieve({
        "class": "s2",
        "dataset": "s2s",
        "date": modelVersionDate,
        "expver": "prod",
        "hdate": hindcastDate,
        "levtype": "sfc",
        "origin": origin,
        "param": "31/34/121/122/136/146/147/151/167/168/169/175/176/177/179/180/181/235/228086/228095/228096/228141/228143/228144/228164/228228",
        "step": "24/to/1488/by/24",
         "stream": "enfh",
        "target": target,
        "time": "CHANGEME00",
        "timenumber": "001/to/32",
        "type": "pf",
    })

if __name__ == '__main__':
    retrieve_BoM_reforecast()

(lightbulb) If the request is "small" you may request more HindcastDates in one go.

...


Useful links

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