Revision as of 14:03, 14 September 2011

Plotting Meteorological Data with Python

This is a very brief introduction to using pygrib and NetCDFFile in order to plot met data in Python. Note that you should read the `Setting Python Paths<PythonPaths>` section in order to be sure that you'll be able to import the appropriate modules.

Let's get started with some test data::

   mkdir test
   cd test
   cp ~sec/kleinproject/FUKU/geop_april* .
   

Now, start ipython in your shell, or create a python file in the test directory::

   ipython
   

Next, let's take care of some basic imports::

import matplotlib.pyplot as plt
import pygrib
from netCDF4 import Dataset as NetCDFFile

Now, we'll write some python code to plot the netcdf variables::

nci = NetCDFFile('geopot_april_01.nc')
nci.variables #will print a listing of the variables (note: nci.variables is a dictionary)
z = nci.variables['z']
z.shape  #what shape is the 'z' array?

for i in range(3):
    plt.figure()
    plt.imshow(z[0,i,:,:]) #we take the i'th slab
    plt.title('netcdf geopot {0}'.format(i))
    plt.colorbar()
    plt.savefig('nc_geopot_{}'.format(i))

Now, let's take a look at the grib data::

grbs = pygrib.open('geop_april_01_2011.grib')
for grb in grbs:
    grb

This will print a listing of all the gribs in the grib file. Make sure we reset the grbs back to the beginning::

grbs.seek(0)
ghs = grbs.select(name='Geopotential')

for i,grb in enumerate(ghs):
    plt.figure()
    g = grb
    plt.imshow(g.values)
    title = g.name + ' at level ' + str(g.level) + ' [' + g.units + ']'
    plt.title(title)
    plt.colorbar()
    plt.savefig(g.name + str(i) +  '.png')

That's it! In your folder you should have some test plots.