wrf.udhel

wrf.udhel(zstag, mapfct, u, v, wstag, dx, dy, bottom=2000.0, top=5000.0, meta=True)

Return the updraft helicity.

This function calculates updraft helicity to detect rotating updrafts. The formula follows Kain et al., 2008, Wea. and Forecasting, 931-952, but this version has controls for the limits of integration, bottom to top, in m AGL. Kain et al used 2000 to 5000 m. The expected range is 25 to 250 m-2/s-2. Keith Brewster, CAPS/Univ. of Oklahoma ; March, 2010

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:

  • zstag (xarray.DataArray or numpy.ndarray) – Geopotential height in [m] that is at least three dimensions with a staggered vertical dimension. The rightmost dimensions are bottom_top_stag x south_north x west_east.

  • mapfct (xarray.DataArray or numpy.ndarray) – The map scale factor on the mass grid. An array of at least two dimensions, whose rightmost two dimensions must be south_north x west_east. If this array is more than two dimensions, they must be the same as zstag’s leftmost dimensions.

  • u (xarray.DataArray or numpy.ndarray) –

    The u component of the wind [m s-1] whose rightmost three dimensions must be bottom_top x south_north x west_east. The leftmost dimensions must be the same as zp’s leftmost dimensions.

    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.

  • v (xarray.DataArray or numpy.ndarray) – The v component of the wind [m s-1] whose rightmost three dimensions must be bottom_top x south_north x west_east. The leftmost dimensions must be the same as zstag’s leftmost dimensions.

  • wstag (xarray.DataArray or numpy.ndarray) – The z component of the wind [m s-1] with the same dimensionality as zstag.

  • dx (float) – The distance between x grid points.

  • dy (float) – The distance between y grid points.

  • bottom (float, optional) – The bottom limit of integration. Default is 2000.0.

  • top (float, optional) – The upper limit of integration. Default is 5000.0.

  • 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 updraft 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

See also

wrf.getvar(), wrf.srhel()