absolute_momentum#

metpy.calc.absolute_momentum(u, v, index='index')#

Calculate cross-sectional absolute momentum (also called pseudoangular momentum).

The cross-sectional absolute momentum is calculated given u- and v-components of the wind along a 2 dimensional vertical cross-section. The coordinates of u and v must match.

Parameters:

  • u (xarray.DataArray) – The input DataArray of the x-component (in terms of data projection) of the wind.

  • v (xarray.DataArray) – The input DataArray of the y-component (in terms of data projection) of the wind.

  • index (str or int, optional) – Denotes the index coordinate of the cross-section, defaults to ‘index’ as set by metpy.interpolate.cross_section

Returns:

absolute_momentum (xarray.DataArray) – Absolute momentum

See also

metpy.interpolate.cross_section, cross_section_components

Notes

As given in [Schultz1999], absolute momentum (also called pseudoangular momentum) is given by:

\[M = v + fx\]

where \(v\) is the along-front component of the wind and \(x\) is the cross-front distance. Applied to a cross-section taken perpendicular to the front, \(v\) becomes the normal component of the wind and \(x\) the tangential distance.

If using this calculation in assessing symmetric instability, geostrophic wind should be used so that geostrophic absolute momentum \(\left(M_g\right)\) is obtained, as described in [Schultz1999].

Changed in version 1.0: Renamed u_wind, v_wind parameters to u, v