使用R netcdf4进行数据提取

Question

I am facing problem to extract data for a region latitude 25 to 32, longitude 81 to 98 from a netcdf4 file sund_WAS-44_ICHEC-EC-EARTH_rcp26_r12i1p1_SMHI-RCA4_v2_day_20510101-20551231.nc .

The lat and lon value are in a matrix of 193*130. I am using R for my purpose. I want to run a loop so that it will give all the values of sund(1826) for each lat,lon .

File sund_WAS-44_ICHEC-EC-EARTH_rcp26_r12i1p1_SMHI-RCA4_v2_day_20510101-20551231.nc (NC_FORMAT_NETCDF4_CLASSIC):"

 5 variables (excluding dimension variables):"
    double lat[rlon,rlat]   "
        standard_name: latitude"
        long_name: latitude"
        units: degrees_north"
    double lon[rlon,rlat]   "
        standard_name: longitude"
        long_name: longitude"
        units: degrees_east"
    char rotated_pole[]   "
        grid_mapping_name: rotated_latitude_longitude"
        grid_north_pole_latitude: 79.95"
        grid_north_pole_longitude: -123.34"
    float sund[rlon,rlat,time]   "
        grid_mapping: rotated_pole"
        _FillValue: 1.00000002004088e+20"
        missing_value: 1.00000002004088e+20"
        standard_name: duration_of_sunshine"
        long_name: Duration of Sunshine"
        units: s"
        coordinates: lon lat"
        cell_methods: time: sum"
    double time_bnds[bnds,time]   "

 4 dimensions:"
   rlat  Size:130"
        standard_name: grid_latitude"
        long_name: latitude in rotated pole grid"
        units: degrees"
        axis: Y"
    rlon  Size:193"
        standard_name: grid_longitude"
        long_name: longitude in rotated pole grid"
       units: degrees"
        axis: X"
    time  Size:1826   *** is unlimited ***"
        standard_name: time"
        units: days since 1949-12-01 00:00:00"
        calendar: standard"
        long_name: time"
        bounds: time_bnds"
        axis: T"
    bnds  Size:2"

    22 global attributes:"        
    Conventions: CF-1.4"
    contact: rossby.cordex@smhi.se"
    creation_date: 2013-12-08-T04:22:00Z"
    experiment: RCP2.6"
    experiment_id: rcp26"
    driving_experiment: ICHEC-EC-EARTH, rcp26, r12i1p1"
    driving_model_id: ICHEC-EC-EARTH"
    driving_model_ensemble_member: r12i1p1"
    driving_experiment_name: rcp26"
    frequency: day"
    institution: Swedish Meteorological and Hydrological Institute, Rossby Centre"
    institute_id: SMHI"
    model_id: SMHI-RCA4"
    rcm_version_id: v2"
    project_id: CORDEX"
    CORDEX_domain: WAS-44"
    product: output"
    references: http://www.smhi.se/en/Research/Research-departments/climate-research-rossby-centre"
    tracking_id: 26296ff2-4f1b-429c-9081-4f9eed7b08d0"
    rossby_comment: 201258: CORDEX West Asia 0.44 deg | RCA4 v2 | ICHEC-EC-EARTH | r12i1p1 | rcp26 | L40"
    rossby_run_id: 201258"
    rossby_grib_path: /nobackup/rossby16/rossby/joint_exp/cordex/201258/raw/"

Answer 1

跨经/ ncks带提取的最简单方法是使用NCO的ncks ： http : ncks

ncks -d latitude,25,32 -d longitude,81,95 your_netcdf.nc -O new_netcdf.nc

Answer 2

your data are cordex data in WAS domain. You should convert your regular coordinate to rotated coordinate and after you can find your coordinate in rlat and rlon variables in nc file. for rotation of your coordinate you can use: Cordex Rotation Or CORDEX Data Extractor https://agrimetsoft.com/Cordex%20Coordinate%20Rotation.aspx https://agrimetsoft.com/CordexDataExtractor.aspx

and after you get rotated coordinate you can use any software or programming such as CDO, Matlab, NCL, R, Netcdf-Extractor