first_derivative_x

first_derivative_x(fs, mode='fdiff', poles_missing_values=False)

Computes the zonal (from West to East) partial derivative of each field in fs in */m units.

Parameters

  • fs (Fieldset) – input 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 derivative 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=”scalar_gradient” option to compute the gradient and taking the zonal component of it

The computations for a field f are based on the following formula:

\[\frac {\partial f}{\partial x} = \frac{1}{R \ cos\phi}\frac{\partial f}{\partial \lambda}\]

where:

  • R is the radius of the Earth

  • \(\phi\) is the latitude

  • \(\lambda\) is the longitude.

Note

See also first_derivative_y(), second_derivative_x(), second_derivative_y() and gradient().