Page History

To help users to improve S2S CMA MARS 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.

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:

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.

#!/usr/bin/env python
from ecmwfapi import ECMWFDataServer
modelVersionDate = "2014-05-01"  # This is the first model version for CMA (babj)
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": "165/166",
    "step": "24/to/1440/by/24",
    "stream": "enfh",
    "target": "data.pf.sfc",
    "time": "00",
    "number": "1/2/3",
    "type": "pf",
})

• The objective of this example is to demonstrate how to make a request efficient by iterating properly over several hindcastYears, hindcastMonths and hindcastDays
• It can be used as a starting point however you need to adapt it to your needseg to set the keyword values (eg hindcastYear).
• In this way you can extend this request to download the whole S2S CMA reforecast,  but don't forget to check CMA availability

 Please note: use the variable "target"  to write each hindcastDate on a separate file .

#!/usr/bin/env python
from ecmwfapi import ECMWFDataServer
server = ECMWFDataServer()

origin = "babj"
modelVersionDate = "2014-05-01"

def retrieve_data(hindcastDate,modelVersionDate,centre):
    target = "target_s2s_%s_%s.grb" % centre % hindcastDate
    server.retrieve({
       "class": "s2",
       "dataset": "s2s",
       "date": modelVersionDate,
       "expver": "prod",
       "hdate": hindcastDate,
       "levtype": "sfc",
       "origin": centre,
       "param": "165",
       "step": "0",
       "stream": "enfh",
       "target": target,
       "time": "00",
       "type": "cf",
})

hindcastYearList = ["2012", "2013"]
hindcastMonthList = ["08", "09"]
hindcastDayList = ["01", "02"]

for hindcastYear in hindcastYearList:
   for hindcastMonth in hindcastMonthList:
       for hindcastDay in hindcastDayList:
           hindcastDate = hindcastYear + hindcastMonth + hindcastDay
               retrieve_data(hindcastDate)

for hindcastYear in ["2012", "2013"]:
    for hindcastMonth in ["08", "09"]:
         for hindcastDay in ["01"  "06" "11" "16" "21" "26"]:
            hindcastDate = hindcastYear+hindcastMonth+hindcastDay
            retrieve_data(hindcastDate,"2014-01-01","ammc")

• CMA re-forecast examples
• ECMWF Web API Home
• CMA re-forecast availability