NCO:使用ncks从NetCDF文件中提取变量

Question

通过输入以下命令，我试图从多变量netcdf文件中提取一个变量：

ncks -v ta temp1.nc out.nc

然而，我看了一下out.nc头，所有的变量都还在。

Tem1.nc和out.nc的头都在下面：

--- temp1.nc header ---
dimensions:
        time = UNLIMITED ; // (124 currently)
        lon = 256 ;
        bnds = 2 ;
        lat = 128 ;
        lev = 40 ;
variables:
        double time(time) ;
                time:standard_name = "time" ;
                time:long_name = "time" ;
                time:units = "days since 1850-1-1" ;
                time:calendar = "365_day" ;
                time:axis = "T" ;
        double lon(lon) ;
                lon:standard_name = "longitude" ;
                lon:long_name = "longitude" ;
                lon:units = "degrees_east" ;
                lon:axis = "X" ;
                lon:bounds = "lon_bnds" ;
        double lon_bnds(lon, bnds) ;
        double lat(lat) ;
                lat:standard_name = "latitude" ;
                lat:long_name = "latitude" ;
                lat:units = "degrees_north" ;
                lat:axis = "Y" ;
                lat:bounds = "lat_bnds" ;
        double lat_bnds(lat, bnds) ;
        double p0 ;
                p0:long_name = "reference pressure" ;
                p0:units = "Pa" ;
        double lev(lev) ;
                lev:standard_name = "atmosphere_hybrid_sigma_pressure_coordinat
                lev:axis = "Z" ;
                lev:positive = "down" ;
                lev:long_name = "hybrid sigma pressure coordinate" ;
                lev:units = "1" ;
                lev:formula_terms = "a: a b: b p0: p0 ps: ps" ;
                lev:bounds = "lev_bnds" ;
                lev:formula = "p = a*p0 + b*ps" ;
        double lev_bnds(lev, bnds) ;
                lev_bnds:standard_name = "atmosphere_hybrid_sigma_pressure_coor
                lev_bnds:units = "1" ;
                lev_bnds:formula_terms = "a: a_bnds b: b_bnds p0: p0 ps: ps" ;
        double a(lev) ;
                a:long_name = "vertical coordinate formula term: ap(k)" ;
                a:units = "Pa" ;
        double b(lev) ;
                b:long_name = "vertical coordinate formula term: b(k)" ;
                b:units = "1" ;
        double a_bnds(lev, bnds) ;
                a_bnds:long_name = "vertical coordinate formula term: ap(k+1/2)
                a_bnds:units = "Pa" ;
        double b_bnds(lev, bnds) ;
                b_bnds:long_name = "vertical coordinate formula term: b(k+1/2)"
                b_bnds:units = "1" ;
        float ps(time, lat, lon) ;
                ps:standard_name = "surface_air_pressure" ;
                ps:long_name = "Surface Air Pressure" ;
                ps:units = "Pa" ;
                ps:comment = "surface pressure, not mean sea level pressure" ;
                ps:original_units = "hPa" ;
                ps:history = "2011-10-17T12:45:37Z altered by CMOR";
                ps:cell_measures = "area: areacella" ;
        float ta(time, lev, lat, lon) ;
                ta:standard_name = "air_temperature" ;
                ta:long_name = "Air Temperature" ;
                ta:units = "K" ;
                ta:_FillValue = 1.e+20f ;
                ta:missing_value = 1.e+20f ;
                ta:original_name = "T" ;
                ta:cell_measures = "area: areacella" ;
                ta:history = "2011-10-17T12:45:37Z altered by CMOR ;
// global attributes:

- out.nc头

dimensions:
        lev = 40 ;
        bnds = 2 ;
        lat = 128 ;
        lon = 256 ;
        time = UNLIMITED ; // (124 currently)
variables:
        double a(lev) ;
                a:long_name = "vertical coordinate formula term: ap(k)" ;
                a:units = "Pa" ;
        double a_bnds(lev, bnds) ;
                a_bnds:long_name = "vertical coordinate formula term: ap(k+1/2)" ;
                a_bnds:units = "Pa" ;
        double b(lev) ;
                b:long_name = "vertical coordinate formula term: b(k)" ;
                b:units = "1" ;
        double b_bnds(lev, bnds) ;
                b_bnds:long_name = "vertical coordinate formula term: b(k+1/2)" ;
                b_bnds:units = "1" ;
        double lat(lat) ;
                lat:standard_name = "latitude" ;
                lat:long_name = "latitude" ;
                lat:units = "degrees_north" ;
                lat:axis = "Y" ;
                lat:bounds = "lat_bnds" ;
        double lat_bnds(lat, bnds) ;
        double lev(lev) ;
                lev:standard_name = "atmosphere_hybrid_sigma_pressure_coordinate" ;
                lev:axis = "Z" ;
                lev:positive = "down" ;
                lev:long_name = "hybrid sigma pressure coordinate" ;
                lev:units = "1" ;
                lev:formula_terms = "a: a b: b p0: p0 ps: ps" ;
                lev:bounds = "lev_bnds" ;
                lev:formula = "p = a*p0 + b*ps" ;
        double lev_bnds(lev, bnds) ;
                lev_bnds:standard_name = "atmosphere_hybrid_sigma_pressure_coordinate" ;
                lev_bnds:units = "1" ;
                lev_bnds:formula_terms = "a: a_bnds b: b_bnds p0: p0 ps: ps" ;
        double lon(lon) ;
                lon:standard_name = "longitude" ;
                lon:long_name = "longitude" ;
                lon:units = "degrees_east" ;
                lon:axis = "X" ;
                lon:bounds = "lon_bnds" ;
        double lon_bnds(lon, bnds) ;
        double p0 ;
                p0:long_name = "reference pressure" ;
                p0:units = "Pa" ;
        float ps(time, lat, lon) ;
                ps:standard_name = "surface_air_pressure" ;
                ps:long_name = "Surface Air Pressure" ;
                ps:units = "Pa" ;
                ps:comment = "surface pressure, not mean sea level pressure" ;
                ps:original_units = "hPa" ;
                ps:history = "2011-10-17T12:45:37Z altered by CMOR" ;
                ps:cell_measures = "area: areacella" ;
        float ta(time, lev, lat, lon) ;
                ta:standard_name = "air_temperature" ;
                ta:long_name = "Air Temperature" ;
                ta:units = "K" ;
                ta:_FillValue = 1.e+20f ;
                ta:missing_value = 1.e+20f ;
                ta:original_name = "T" ;
                ta:cell_measures = "area: areacella" ;
                ta:history = "2011-10-17T12:45:37Z altered by CMOR" ;
        double time(time) ;
                time:standard_name = "time" ;
                time:long_name = "time" ;
                time:units = "days since 1850-1-1" ;
                time:calendar = "365_day" ;
                time:axis = "T" ;

// global attributes:

我以为out.nc上只有ta。我没有从ncks收到任何错误消息。

我在这里做错什么了？我很感谢你的帮助。

谢谢。

Answer 1

发生此行为的原因是，默认情况下，NCO提取与请求的变量“关联”的所有变量。这样，用户就可以得到他们所需要的一切，而不必自己去寻找。换句话说，这是一个特性，而不是一个bug。要只提取显式请求的变量，请使用-C开关、文档化的这里。

ncks -C -v ta temp1.nc out.nc

这些文档还展示了如何删除CF-约定相关的变量，同时使用各种较长的选项保留坐标。

Answer 2

仅仅为了让另一个命令行替代NCO，您也可以使用CDO，

该命令是：

cdo selvar,variable_name input.nc output.nc 

如果你没有它，你可以用ubuntu，mint等安装它

sudo apt-get install cdo