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What is the objective of this page?
To help users to improve S2S ECMWFMARS requests performance via the WebAPI.
A good understanding of the MARS efficiency issues is essential especially for users that are interested in downloading large amounts of data.
How is the S2S reforecast data organised in MARS?
In general it is organised, as a huge tree, with the indentation below, showing different levels down that tree:
- centre (BoM, 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 (2014-01-01 or ...)
- hindcast dates (2013-09-01, 2013-09-06, 2013-09-11, 2013-09-16, 2013-09-21, 2013-09-26, ...)
- time and steps
- members (for perturbed forecast)
- levels (for pl or pt)
- parameters
- levels (for pl or pt)
- members (for perturbed forecast)
- time and steps
- hindcast dates (2013-09-01, 2013-09-06, 2013-09-11, 2013-09-16, 2013-09-21, 2013-09-26, ...)
- model version date (2014-01-01 or ...)
- type of level (single level or pressure level or potential temperature)
- type of data (control forecast or perturbed forecast)
- realtime or reforecast
What would be the natural way to group requests?
The idea is to request as much data as possible from the same tape file. The natural way to group requests would be:
all parameters, all levels, all members, all time-steps for 1 hindcast date for a type of level for a type
Note the following:
- 'all' means 'all' that the user wants. It doesn't have to be all parameters.
- 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.
Best practise to iterate over all hindcastDates of several hindcastYears for BoM
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.
At this point you may wish to check ECMWFavailability and to view a ECMWFrequest
for hindcastYear in hindcastYears
for hindcastMonth in hindcastMonths
for hindcastDay in hindcastDays
hindcastDate = hindcastYear-hindcastMonth-hindcastDay
S2S-request(hindcastDate)
Web-API examples:
A ECMWFreforecast request for all the available hindcastDates
- The objective of this example is to demonstrate how to iterate efficiently over all the available hindcastYears, hindcastMonths and hindcastDays for a ECMWFreforecast request
- It can be used as a starting point, however you need to keep in mind that you have to adapt it to your needs eg 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 ECMWFreforecast. Don't forget to check ECMWFavailability
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.
#!/usr/bin/env python
from ecmwfapi import ECMWFDataServer
server = ECMWFDataServer()
origin = "ecmf"
modelVersionDate = "2014-01-01"
def retrieve_ECMWF_reforecast():
"""
A function to demonstrate how to iterate efficiently over all hindcastYears, hindcastMonths etc
for a particular ECMWF_reforecast_request.
Change the variables below to adapt the iteration to your needs
"""
hindcastYearStart = 1981
hindcastYearEnd = 2013
hindcastMonthStart = 1
hindcastMonthEnd = 12
# ECMWFavailability 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
for hindcastDay in hindcastDays:
hindcastDate = '%04d%02d%02d' % (
hindcastYear, hindcastMonth, hindcastDay)
hindcastDates.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)
ECMWF_reforecast_pf_pl_request("/".join(hindcastDates), pfplTarget)
#Step 5: Get all the available perturbed forecast, surface data
pfsfcTarget = "%s_%s_%04d%02d.grb" % (
origin, "pfsfc", hindcastYear, hindcastMonth)
ECMWF_reforecast_pf_sfc_request("/".join(hindcastDates), pfsfcTarget)
def ECMWF_reforecast_pf_pl_request(hindcastDate, target):
"""
A ECMWFreforecast, 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": modelVersionDate,
"expver": "prod",
"hdate": hindcastDate,
"levtype": "pl",
"levelist": "10/50/100/200/300/500/700/850/925/1000",
"origin": origin,
"param": "130/131/132/133/135/156",
"step": "24/to/1488/by/24",
"stream": "enfh",
"target": target,
"time": "00",
"number": "1/to/32",
"type": "pf",
})
def ECMWF_reforecast_pf_sfc_request(hindcastDate, target):
"""
A ECMWFreforecast, 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": "00",
"number": "1/to/32",
"type": "pf",
})
if __name__ == '__main__':
retrieve_ECMWF_reforecast()
Useful links