how to write attribute in netcdf file when creating it

I have extracted information from one netcdf file and writting it to another netcdf file.I have created the netcdf file by

ncdisp('H:\era\ERA_Q.nc');
lev=ncread('H:\era\ERA_Q.nc','level');
lev1=lev*100;
lat=ncread('H:\era\ERA_Q.nc','latitude');
lon=ncread('H:\era\ERA_Q.nc','longitude');
q=ncread('H:\era\ERA_Q.nc','q');
Q1=single(q);
nccreate('test_files.nc','lat','Dimensions',{'lat' 3});
nccreate('test_files.nc','lon','Dimensions',{'lon' 4});
nccreate('test_files.nc','time','Dimensions',{'time' 9862});
nccreate('test_files.nc','lev','Dimensions',{'lev' 4});
nccreate('test_files.nc','q','datatype','single','Dimensions',{'lon' 4 'lat' 3 'lev' 4 'time' 9862});
% ncdisp('test_files.nc');
ncwrite('test_files.nc','lat',31.5000:.5:32.5000);
ncwrite('test_files.nc','lon',76.5000:.5:78);
ncwrite('test_files.nc','q',Q1);
ncdisp('test_files.nc');

I have to add attributes like

time
           Size:       18262x1
           Dimensions: time
           Datatype:   double
           Attributes:
                       long_name           = 'Time variable'
                       units               = 'days since 1950-01-01 00:00:00'
                       _CoordinateAxisType = 'Time'
    lat 
           Size:       6x1
           Dimensions: rlat
           Datatype:   double
           Attributes:
                       standard_name       = 'latitude'
                       long_name           = 'latitude'
                       units               = 'degrees north'
                       _CoordinateAxisType = 'Lat'
    lon 
           Size:       9x1
           Dimensions: rlon
           Datatype:   double
           Attributes:
                       standard_name       = 'longitude'
                       long_name           = 'longitude'
                       units               = 'degrees east'
                       _CoordinateAxisType = 'Lon'
    lev 
           Size:       4x1
           Dimensions: lev
           Datatype:   double
           Attributes:
                       standard_name       = 'pressure'
                       long_name           = 'pressure'
                       units               = 'Pa'
                       _CoordinateAxisType = 'Z'
    Q   
           Size:       6x9x4x18262
           Dimensions: rlat,rlon,lev,time
           Datatype:   single
           Attributes:
                       standard_name = 'specific humidity'
                       long_name     = 'Specific humidity'
                       units         = 'kg kg**-1'
                       missing_value = -1e+04

How can I do it?

Answer 1

[KSSV]

doc ncwrite and ncwriteatt

https://in.mathworks.com/help/matlab/ref/ncwrite.html

[Tanmoyee Bhattacharya]

I have done.

end
ncdisp('H:\era\ERA_Q.nc');
lev=ncread('H:\era\ERA_Q.nc','level');
lev1=lev*100;
lat=ncread('H:\era\ERA_Q.nc','latitude');
lon=ncread('H:\era\ERA_Q.nc','longitude');
q=ncread('H:\era\ERA_Q.nc','q');
q1=single(q);
nccreate('test_files.nc','lat','Dimensions',{'lat' 3});
ncwriteatt('test_files.nc', 'lat', 'standard_name', 'latitude');
ncwriteatt('test_files.nc', 'lat', 'long_name', 'latitude');
ncwriteatt('test_files.nc', 'lat', 'units', 'degrees north');
ncwriteatt('test_files.nc', 'lat', '_CoordinateAxisType', 'Lat');
% ncwriteatt('test_files.nc','/','standard_name','latitude');
nccreate('test_files.nc','lon','Dimensions',{'lon' 4});
ncwriteatt('test_files.nc', 'lon', 'standard_name', 'longitude');
ncwriteatt('test_files.nc', 'lon', 'long_name', 'longitude');
ncwriteatt('test_files.nc', 'lon', 'units', 'degrees north');
ncwriteatt('test_files.nc', 'lon', '_CoordinateAxisType', 'Lon');
nccreate('test_files.nc','time','Dimensions',{'time' 9862});
ncwriteatt('test_files.nc', 'time', 'long_name', 'Time variable');
ncwriteatt('test_files.nc', 'time', 'units', 'days since 1979-01-01 00:00:00');
ncwriteatt('test_files.nc', 'time', '_CoordinateAxisType', 'Time');
nccreate('test_files.nc','lev','Dimensions',{'lev' 4});
ncwriteatt('test_files.nc', 'lev', 'standard_name', 'pressure');
ncwriteatt('test_files.nc', 'lev', 'long_name', 'pressure');
ncwriteatt('test_files.nc', 'lev', 'units', 'Pa');
ncwriteatt('test_files.nc', 'lev', '_CoordinateAxisType', 'Z');
nccreate('test_files.nc','Q','datatype','single','Dimensions',{'lon' 4 'lat' 3 'lev' 4 'time' 9862});
ncwriteatt('test_files.nc', 'Q', 'standard_name', 'specific humidity');
ncwriteatt('test_files.nc', 'Q', 'long_name', 'Specific humidity');
ncwriteatt('test_files.nc', 'Q', 'units', 'kg kg**-1');
ncwriteatt('test_files.nc', 'Q', 'missing_value', '-1e+04');
% ncdisp('test_files.nc');
ncwrite('test_files.nc','lat',31.5000:.5:32.5000);
ncwrite('test_files.nc','lon',76.5000:.5:78);
ncwrite('test_files.nc','Q',q1);
ncdisp('test_files.nc');

Thank you.

[Charles Lee]

Thank you sooo much for sharing the code!!!!!

[UTKARSH VERMA]

Please guide me how to write global attributes to the same file?

Also, I want to know how to create nc file in Matlab so that it can be read by grads without using descriptor file.

[GS Louw]

When using the function ncwriteatt(filename,location,attname,attvalue)For global attributes you use '/' at location, so an example would look like the below:

ncwriteatt('test_files.nc', '/', 'geospatial_lat_units','degrees_north');