how to get variables from a netcdf file

Question

Santo 2023-9-24

0
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此问题的直接链接

https://ww2.mathworks.cn/matlabcentral/answers/2025097-how-to-get-variables-from-a-netcdf-file

回答： Luis Jesús Olvera Lazcano 2023-9-27

Hi, could anyone help me? I imported this netcdf file of a weather wrf model, which analyzed some parameters for the month of June 2017. I don't know how to see the temperature variable, given that it has 3 dimensions (171x171x720). How can I get something like this for this variable, for example a column for the date (01/06/2017 00:00:00, 01:00:00 etc..) and a column for the temperature 15.7, 13.2 etc. also having the coordinates (lat,lon) as reference.

Thanks so much to anyone who can help me :)

ncdisp(filename)
filename =    'meteo_jun.nc'
Source:
C:\Users\sanny\linux\meteo_jun.nc
Format:
64bit
Global Attributes:
TITLE                          = ' OUTPUT FROM WRF V3.9.1.1 MODEL'
START_DATE                     = '2017-06-01_00:00:00'
SIMULATION_START_DATE          = '2017-05-28_00:00:00'
WEST-EAST_GRID_DIMENSION       = 172
SOUTH-NORTH_GRID_DIMENSION     = 172
BOTTOM-TOP_GRID_DIMENSION      = 56
DX                             = 1333.333
DY                             = 1333.333
Dimensions:
Time        = 720   (UNLIMITED)
south_north = 171
west_east   = 171
DateStrLen  = 19
Variables:
T2         
Size:       171x171x720
Dimensions: west_east,south_north,Time
Datatype:   single
Attributes:
FieldType   = 104
MemoryOrder = 'XY '
description = 'TEMP at 2 M'
units       = 'K'
stagger     = ''
coordinates = 'XLONG XLAT XTIME'
Times      
Size:       19x720
Dimensions: DateStrLen,Time
Datatype:   char
XLAT       
Size:       171x171
Dimensions: west_east,south_north
Datatype:   single
Attributes:
FieldType    = 104
MemoryOrder  = 'XY '
description  = 'LATITUDE, SOUTH IS NEGATIVE'
units        = 'degree_north'
stagger      = ''
coordinates  = 'XLONG XLAT'
cell_methods = 'Time: mean'
XLONG      
Size:       171x171
Dimensions: west_east,south_north
Datatype:   single
Attributes:
FieldType    = 104
MemoryOrder  = 'XY '
description  = 'LONGITUDE, WEST IS NEGATIVE'
units        = 'degree_east'
stagger      = ''
coordinates  = 'XLONG XLAT'
cell_methods = 'Time: mean'

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dpb 2023-9-25

As per usual, you'd probably find more folks willing to poke at it in more detail if you were to attach the file for them to work with...

But, in general, you will use find() or ismembertol() to locate the position in the XLONG, XLAT arrays of the desired coordinates, then use that pair of values to index into the T2() array by the third dimension as T2(ix,iy,:) that will return a vector if ix,iy are single points. That will depend upon whether the grid is regular as presume will be, but we can't see it from here to know for absolute certain.

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Answer 1

Luis Jesús Olvera Lazcano 2023-9-27

0
链接

此回答的直接链接

https://ww2.mathworks.cn/matlabcentral/answers/2025097-how-to-get-variables-from-a-netcdf-file#answer_1320399

在 MATLAB Online 中打开

In order to see the temperature variable, you will need to plot in an specified time. To find a specific date, it would be better to have time variable as datetime:

mystring = ncread(filename,'Times');
time = datetime(my_string,'InputFormat','yyyy-MM-dd HH:mm:ss.S'); % where my_string is your t variable

To find an specific datetime, for example "01/06/2017":

date = datetime('2017-06-01'); % considering only one date
td = ismember(time,date); % logical values, being 1 the only ones with the date specified
% Extract only one date in T2 data.
T2date = t2(:,:,td); % this will extract only the times that have the date in question.
[LAT LON] = meshgrid(lat,lon);
figure(1)
for i=1:length(T2date(1,1,:)) % to show time per time the T2 values in a LAT LON grid
    pcolor(LAT,LON,t2date(:,:,i)), shading interp
    pause(0.5) % in order to see each time with a 0.5 seconds duration
end