def nc_div(nc, tidx, grd=None):
if grd is None:
grd = nc_grid(nc)
nc = Dataset(nc)
u = nc.variables['u'][tidx]
v = nc.variables['v'][tidx]
return ( (diff(u, axis=-1)/diff(grd.x_u, axis=-1))[...,1:-1,:] + \
(diff(v, axis=-2)/diff(grd.y_v, axis=-2))[...,:,1:-1] )
def nc_curl(nc, tidx, grd=None):
if grd is None:
grd = nc_grid(nc)
nc = Dataset(nc)
u = nc.variables['u'][tidx]
v = nc.variables['v'][tidx]
return ( diff(v, axis=-1)/diff(grd.x_v, axis=-1) - \
diff(u, axis=-2)/diff(grd.y_u, axis=-2) )
def nc_div(nc, tidx, grd=None):
if grd is None:
grd = nc_grid(nc)
nc = Dataset(nc)
u = nc.variables['u'][tidx]
v = nc.variables['v'][tidx]
return ( (diff(u, axis=-1)/diff(grd.x_u, axis=-1))[...,1:-1,:] + \
(diff(v, axis=-2)/diff(grd.y_v, axis=-2))[...,:,1:-1] )
def nc_curl(nc, tidx, grd=None):
if grd is None:
grd = nc_grid(nc)
nc = Dataset(nc)
u = nc.variables['u'][tidx]
v = nc.variables['v'][tidx]
return ( diff(v, axis=-1)/diff(grd.x_v, axis=-1) - \
diff(u, axis=-2)/diff(grd.y_u, axis=-2) )
def nc_pstrain(nc, tidx, grd=None):
if grd is None:
grd = nc_grid(nc)
nc = Dataset(nc)
u = nc.variables['u'][tidx]
v = nc.variables['v'][tidx]
ex = (diff(u, axis=-1) / diff(grd.x_u, axis=-1))[..., 1:-1, :]
ey = (diff(v, axis=-2) / diff(grd.y_v, axis=-2))[..., :, 1:-1]
gamma = shrink ( diff(u, axis=-2)/diff(grd.y_u, axis=-2) + \
diff(v, axis=-1)/diff(grd.x_v, axis=-1) , ex.shape)
return 0.5*(ex + ey) + sqrt( (0.5*(ex - ey))**2 + (0.5*gamma)**2 ), \
0.5*(ex + ey) - sqrt( (0.5*(ex - ey))**2 + (0.5*gamma)**2 )
def nc_pstrain(nc, tidx, grd=None):
if grd is None:
grd = nc_grid(nc)
nc = Dataset(nc)
u = nc.variables['u'][tidx]
v = nc.variables['v'][tidx]
ex = (diff(u, axis=-1)/diff(grd.x_u, axis=-1))[...,1:-1,:]
ey = (diff(v, axis=-2)/diff(grd.y_v, axis=-2))[...,:,1:-1]
gamma = shrink ( diff(u, axis=-2)/diff(grd.y_u, axis=-2) + \
diff(v, axis=-1)/diff(grd.x_v, axis=-1) , ex.shape)
return 0.5*(ex + ey) + sqrt( (0.5*(ex - ey))**2 + (0.5*gamma)**2 ), \
0.5*(ex + ey) - sqrt( (0.5*(ex - ey))**2 + (0.5*gamma)**2 )