Taking a quick look at velocity vectors from U and V fields in NetCDF files.

#  Invoke ipython with the scipy/numpy/pylab capabilities.
ipython -pylab

#  Import the capabilities of the Python-NetCDF package. 
import netCDF3,netCDF4

#  Create an object containing the NetCDF file file.nc.
nc = netCDF3.Dataset('file.nc','r+')

#  Extract the U and V velocity variables called Uwind and Vwind in the NetCDF file.
U = nc.variables['Uwind'][:]
V = nc.variables['Vwind'][:]

#  Create a vector plot choosing the first time step and every 5th spatial step.
quiver(U[1,::5,::5], V[1,::5,::5])

Interrogating a NetCDF file to discover what lies within.

#  Create an object containing the NetCDF file file.nc.
nc = netCDF3.Dataset('file.nc','r+')

#  Discover the variables therein.
nc.variables

{'Uwind': ,
 'Vwind': ,
 'lat_rho': ,
 'lon_rho': ,
 'wind_time': }

#  Extract the Uwind variable field into u.
u = nc.variables['Uwind'][:]

#  Find the shape of u.
u.shape

(248, 246, 288)

#  Discover the dimension names therein.
nc.dimensions

{'eta_rho': ,
 'wind_time': ,
 'xi_rho': }

#  Find the size of a given dimension.
len(nc.dimensions['wind_time'])

248

#  Discover the file format.
nc.file_format

#  Discover the global attributes.
nc.ncattrs()

['title',
 'institution',
 'source',
 'history',
 'note1',
 'note2',
 'note3',
 'note4']

#  Discover a global attribute value.
nc.title

'ECMWF Global Interim Winds Interpolated to ROMS Oman Grid'

#  Discover variable attribute values.  First, create an object, e.g.
uu = nc.variables['Uwind']

#  Next, find out the attributes for that variable.
uu.ncattrs()

['units',
 'long_name',
 'time',
 'standard_units',
 'standard_name',
 'origin',
 'model',
 'center',
 'geographical_limits']

# Finally, find the value for a specific attribute.
uu.units

'meter second-1'