Python - How to get variable from netcdf file on a specific location and at different level

Question

I am learning on how to plot various variables from WRF output netcdf file. My requirement is to extract variables for a certain lat/lon (8.4875° N, 76.9525° E) in order to plot SkewT profiles using the matplotlib package.

I found a similar question on this SO page netcdf4 extract for subset of lat lon. However, its location is a set of boundaries.

Thanks for your comment. When I executed your code it returned 1632 and 43 for lat 8.4 and lon 76.95. This is no way close to the actual Lat & Lon I would expect. — sundar_ima
– sundar_ima, Commented Dec 21, 2015 at 16:03
76.95 E is -76.95 in decimal degrees. I added code to show how to test the results at the answer above. — Eric Bridger
– Eric Bridger, Commented Dec 21, 2015 at 18:36
Well I have got the index error IndexError: index 1632 is out of bounds for axis 0 with size 73. Does it mean that the lat and lon is not available in the file? — sundar_ima
– sundar_ima, Commented Dec 21, 2015 at 19:10
I am not at all familiar with the WRF NetCDF file format. A quick looks suggests that the lat,lon columns might be named south_north and west_east. Do you have the url where you got the WRF file. — Eric Bridger
– Eric Bridger, Commented Dec 23, 2015 at 17:06

jhamman · Accepted Answer · 2015-12-21 02:36:01Z

1

Check out xray. You'll have to do some work to make the SkewT chart but accessing and summarizing the netCDF Dataset and variables will be pretty easy. Just a few examples below.

import xray

ds = xray.open_dataset('your_wrf_file.nc')

ds_point = ds.sel(lon=76.9525, lat=8.4875)

ds_point['Temperature'].plot()  # plot profile at point assuming Temperature had dimensions of (level, lat, lon)

df = ds_point.to_dataframe()  # export dataset to Pandas.DataFrame

temp_array = ds_point['Temperature'].values  # access the underlying numpy array of the "Temperature" variable

answered Dec 21, 2015 at 2:36

jhamman

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2 Comments

sundar_ima Over a year ago

Your code gives me a key error. I have changed the key to XLAT and XLONG which is equivalent of lon and lat. But still same issue.

jhamman Over a year ago

You didn't provide a sample file so this was just to give you a rough idea of how this could be done.

ClimateUnboxed · Accepted Answer · 2017-09-20 06:11:03Z

0

What I usually do is extract the nearest gridpoint to the column using CDO from the command line before using ncl,python,R etc for plotting:

cdo remapnn,lon=76.9525/lat=8.4875 wrf_file.nc pnt_file.nc

answered Sep 20, 2017 at 6:11

ClimateUnboxed

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