Basic usage

This section describes the basic usage of the VectorWind objects in a generic way that is applicable to all interfaces.

Importing a VectorWind object

The VectorWind objects are stored in interface specific modules: windspharm.<interface>.VectorWind. To import the standard interface:

from windspharm.standard import VectorWind

the iris interface:

from windspharm.iris import VectorWind

the xarray interface:

from windspharm.xarray import VectorWind

and the cdms interface:

from windspharm.cdms import VectorWind

Creating a VectorWind object

Creating a VectorWind object from eastward and northward wind components u and v can be as simple as:

w = VectorWind(u, v)

In the case of the windspharm.standard.VectorWind interface there is a keyword argument gridtype which should be set to either ‘regular’ for equally spaced grids or ‘gaussian’ for Gaussian grids (the default is ‘regular’):

w = VectorWind(u, v, gridtype='gaussian')

Computing with VectorWind

To perform a computation you call one of the methods of the VectorWind object. For example, to compute the vorticity and divergence:

vrt, div = w.vrtdiv()

All the computation methods take an optional truncation keyword argument which can be used to truncate the spectral coefficients before doing the computation.

It is also possible to compute gradients of scalar fields, which is useful for many applications. For example, to compute the gradients of absolute vorticity:

absvrt = w.absolutevorticity()
absvrt_u, absvrt_v = w.gradient(absvrt)

Note

Some of the quantities can be computed separately or part of another computation e.g. vorticity() and divergence() or vrtdiv(). If you only want one of the results then you can call the single version, but if you want both the method that computes both at once will always be faster than calling both single versions.