Vorticity and divergence

Calculate vorticity and divergence from u and v wind components using vorticity() and divergence() functions.

fn = os.path.join(migl.get_sample_folder(), 'GrADS', 'model.ctl')
f = addfile(fn)
u = f['U'][0,0,:,:]
v = f['V'][0,0,:,:]
lat = u.dimvalue(0)
lon = u.dimvalue(1)
glon, glat = np.meshgrid(lon, lat)
dx, dy = meteolib.lat_lon_grid_deltas(glon, glat)
vort = meteolib.vorticity(u, v, dx, dy)
divg = meteolib.divergence(u, v, dx, dy)

levs = arange(-3e-5, 3e-5, 1e-6)
subplot(2,1,1,axestype='map')
geoshow('continent')
contourf(lon, lat, vort, levs)
title('Vorticity')
colorbar(orientation='horizontal', aspect=50)
subplot(2,1,2,axestype='map')
geoshow('continent')
contourf(lon, lat, divg, levs)
title('Divergence')
colorbar(orientation='horizontal', aspect=50)