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The derivatives are computed with a second order finite-difference approximation. The resulting fields contain missing values on the poles. If the input fields are horizontal wind components the GRIB paramId of the resulting field is set to 138 (relative vorticity). Please note that this function is only implemented for regular latitude-longitude grids.

number w_from_omega(omega: number,  t: number,  p: number)

vector w_from_omega(omega: number,  t: number,  p: number)

fieldset w_from_omega(omega: fieldset, t: fieldset)

fieldset w_from_omega(omega: fieldset,  t: fieldset,  p: fieldset)

Computes the hydrostatic vertical velocity from  pressure velocity (omega) for a given temperature and pressure, where

• • omega: pressure velocity (Pa/s)
  • t: temperature (K)
  • p: pressure (Pa)

The result is the vertical velocity in m/s units. On error  nil is returned. The following rules are applied when omega is a fieldset:

• • if omega is a pressure level fieldset no pressure argument is needed
  • if omega is defined on ECMWF model levels (hybrid/eta) p is either a single LNSP (logarithm of surface pressure, identified by paramId=152) field or a fieldset defining the pressure on the levels of omega
  • for other level types p is a fieldset defining the pressure on the levels of omega

The computation is based on the following hydrostatic formula:

w = - \frac{\omega T R_{d}}{p g}

where

• Rd is the specific gas constant for dry air (287.058 J/(kg K)).
• g is the gravitational acceleration (9.81 m/s²)

This functions was introduced in version 5.10.0.