pressure_derivative

pressure_derivative(f[, p])

New in Metview version 5.13.0.

Computes the vertical pressure derivative.

Parameters

  • f (list, ndarray, Fieldset) – input data defined on a given set of pressure values

  • p (number, ndarray or Fieldset) – pressure (Pa)

Return type

same type as f or None

The result is the vertical pressure derivative in */Pa units. The following rules are applied when f is a Fieldset:

  • if f is a pressure level Fieldset no p is needed

  • if f is defined on ECMWF model levels (hybrid/eta) p must be either a single LNSP (logarithm of surface pressure, identified by paramId=152) field or a Fieldset defining the pressure on the same levels as f (see pressure())

  • for other level types p must be a Fieldset defining the pressure on the same levels as f.

In the computations, first the values are sorted by pressure, then a non-uniform central difference scheme (one-sided difference at the bottom and top) is used to estimate the derivatives. The results are then re-sorted to appear in the same order as in f. This allows for the following type of computations:

import metview as mv

# read fields defined on the same set of, potentially unsorted,
# pressure levels. I.e. the fields in f1 and f2 are properly lined
# up in terms of pressure.
f1 = mv.read("data1.grib")
f2 = mv.read("data2.grib")

# the fields are still lined up for computing r since
# pressure_derivative() keeps the original field ordering
r = f2 * mv.pressure_derivative(f1)