Much of the data provided by the Copernicus Atmosphere Monitoring Service (CAMS), the Copernicus Climate Change Service (C3S), and by meteorological centres like ECMWF comes in GRIB or NetCDF format. This article gives examples how to extract data for a specific location and/or time from a GRIB or NetCDF file.
In this example we work with ERA5 data, hourly surface pressure (sp) for the month 2010-08, as specified in this data retrieval script:
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#!/usr/bin/env python
from ecmwfapi import ECMWFDataServer
server = ECMWFDataServer()
server.retrieve({
"class": "ea",
"dataset": "era5",
"date": "2010-08-01/to/2010-08-31",
"expver": "1",
"levtype": "sfc",
"param": "134.128",
"stream": "oper",
"time": "00/to/23/by/1",
"type": "an",
"target": "e5-sp-201008xx.grib",
})
server.retrieve({
"class": "ea",
"dataset": "era5",
"date": "2010-08-01/to/2010-08-31",
"expver": "1",
"levtype": "sfc",
"param": "134.128",
"stream": "oper",
"time": "00/to/23/by/1",
"type": "an",
"grid": "0.5/0.5",
"format": "netcdf",
"target": "e5-sp-201008xx.nc",
})
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This script retrives a GRIB file 'e5-sp-201008xx.grib' and a NetCDF file 'e5-sp-201008xx.nc'.
Looking up data values in GRIB
We want to look up the surface pressure (sp) data value for 2010-08-05 00:00, at the model point closest to our target location lon=7.36 lat=43.89
Install ECMWF ecCodes, then look up the data value with the grib_ls command:
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grib_ls -l 43.89,7.36,1 -w dataDate=20100805,dataTime=0000 -p shortName e5-sp-201008xx.grib |
Output:
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... shortName value sp 88510 ... Input Point: latitude=43.89 longitude=7.36 Grid Point chosen #3 index=84109 latitude=43.98 longitude=7.50 distance=15.11 (Km) ... |
Looking up data values in NetCDF
We want to look up the surface pressure (sp) data value for 2010-08-05 00:00, at the model point closest to our target location lon=7.36 lat=43.89
Install CDO, then look up the data value:
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cdo -outputtab,lon,lat,date,time,value -selyear,2010 -selmonth,08 -selday,05 -seltime,00:00 -remapnn,lon=7.36_lat=43.89 e5-sp-201008xx.nc |
Output:
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# lon lat date time value ... 7.36 43.89 2010-08-05 00:00:00 88360.6 ... |