NCL Home > Documentation > Functions > WRF

# wrf_omega

Calculates approximate omega in C, given vertical velocity, water vapor mixing ratio, temperature, and pressure from WRF model output.

Available in version 6.2.0 and later.

## Prototype

```	function wrf_omega (
qv  : numeric,
t   : numeric,
v   : numeric,
p   : numeric
)

return_val  :  float or double
```

## Arguments

qv

Water vapor mixing ratio in [kg/kg]. The rightmost dimensions are bottom_top x south_north x west_east.

t

Temperature in [K]. An array with the same dimensionality as qv.

v

Vertical velocity in [m/s]. An array with the same dimensionality as qv.

p

Pressure in [mb]. An array with the same dimensionality as qv.

## Return value

Approximate omega [dp/dt]. The rightmost three dimensions will be bottom_top x south_north x west_east, and the leftmost dimensions, if any, will be the same as qv's. The array will contain the same named dimensions as qv; otherwise, the rightmost two dimensions will be named "south_north" and "west_east". The type will be double if any of the input is double, and float otherwise.

## Description

This function calculates approximate omega in C, given vertical velocity, water vapor mixing ratio, temperature, and pressure from WRF model output.

You can use wrf_user_getvar with an argument of "omg" to calculate this diagnostic.

The return variable will contain two attributes:

return_val@description = "Omega"
return_val@units = "Pa/s"

See the full list of WRF functions.

## Examples

Note: for WRF variable names and their definitions, you can easily check them by using "ncl_filedump":

```  ncl_filedump wrfout_d01_2000-01-24_12:00:00.nc
```

Example 1

You can see some other example scripts and their resultant images at:

http://www2.mmm.ucar.edu/wrf/OnLineTutorial/Graphics/NCL/