divergence

divergence(fx, fy, mode='fdiff', poles_missing_values=False)

Computes the divergence of 2-dimensional vector fields.

Parameters

  • fx (Fieldset) – zonal (west-east) vector component fieldset

  • fy (Fieldset) – meridional (south-north) vector component fieldset

  • mode ({"fdiff", "felem"}, default: "fdiff") – specifies the computation mode (see below)

  • poles_missing_values (bool, default: False) – puts missing values at the poles when mode is “felem”.

Return type

Fieldset

The numerical method to compute the divergence is based on the value of mode.

When mode is “fdiff”:

  • a second order finite-difference approximation is used

  • the output fields contain missing values at the poles

  • only works for regular latitude-longitude grids

When mode is “felem”:

  • a finite-element technique is used

  • works with (regular and reduced) latitude-longitude and Gaussian grids

  • no missing values are allowed in fs!

  • the computations are performed by using regrid() with the nabla=”uv_divergence” option

The computations for a vector field f=(fx,fy) are based on the following formula:

\[div(f) = \frac{1}{R \ cos\phi}\frac{\partial f_x}{\partial \lambda} + \frac{1}{R}\frac{\partial f_y}{\partial \phi} - \frac{f_y}{R}tan\phi\]

where:

  • R is the radius of the Earth (in m)

  • \(\phi\) is the latitude

  • \(\lambda\) is the longitude.

If fx and fy are horizontal wind components the ecCodes paramId of the resulting field is set to 155 (=divergence).

Note

See also vorticity(), shear_deformation() and stretch_deformation().