wrf.srhel¶

wrf.srhel(u, v, height, terrain, top=3000.0, meta=True)¶

Return the storm relative helicity.

This function calculates storm relative helicity from WRF ARW output. SRH (Storm Relative Helicity) is a measure of the potential for cyclonic updraft rotation in right-moving supercells, and is calculated for the lowest 1-km and 3-km layers above ground level. There is no clear threshold value for SRH when forecasting supercells, since the formation of supercells appears to be related more strongly to the deeper layer vertical shear. Larger values of 0-3 km SRH (greater than 250 m2 s-2) and 0-1 km SRH (greater than 100 m2 s-2), however, do suggest an increased threat of tornadoes with supercells. For SRH, larger values are generally better, but there are no clear “boundaries” between non-tornadic and significant tornadic supercells.

This is the raw computational algorithm and does not extract any variables from WRF output files. Use wrf.getvar() to both extract and compute diagnostic variables.

Parameters:

u (xarray.DataArray or numpy.ndarray) – The u component of the wind that must have at least three dimensions. The rightmost dimensions are bottom_top x south_north x west_east.
v (xarray.DataArray or numpy.ndarray) – The v component of the wind with the same dimensionality as u.
height (xarray.DataArray or numpy.ndarray) – Geopotential height in [m] with the same dimensionality as u.
terrain (xarray.DataArray or numpy.ndarray) –
Terrain height in [m]. This is at least a two-dimensional array with the same dimensionality as u, excluding the bottom_top dimension.

Note

This variable must be supplied as a xarray.DataArray in order to copy the dimension names to the output. Otherwise, default names will be used.
top (float) – The height of the layer below which helicity is calculated (meters above ground level).
meta (bool) – Set to False to disable metadata and return numpy.ndarray instead of xarray.DataArray. Default is True.

Warning

The input arrays must not contain any missing/fill values or numpy.nan values.

Returns:	The storm relative helicity. If xarray is enabled and the meta parameter is True, then the result will be an `xarray.DataArray` object. Otherwise, the result will be a `numpy.ndarray` object with no metadata.
Return type:	`xarray.DataArray` or `numpy.ndarray`