Docs for bunkers_storm_motion are very sparse

[edrewitz]

What went wrong?

I'm making a sounding program and I have error messages only part of the time pop up with respect to getting the 0-6km data. I looked at the raw data for both a dataset that works and one that doesn't work and they have the same bottom bound. The one that works is PANC at 5/30/2020 12z and an example of one that doesn't work is PANC at 2/12/2022 00z. I'm not sure what is going on here. I specifically have this issue when trying to calculate bunkers storm motion.

Operating System

Linux

Version

metpy 1.3.0

Python Version

Python 3.9.12

Code to Reproduce

# 0-6km
(pres_trimmed, u_trimmed1, v_trimmed1,
    speed_trimmed1, height_trimmed1) = mpcalc.get_layer(d['pressure'],
                                                    d['u_wind'],
                                                    d['v_wind'],
                                                    d['speed'],
                                                    d['height'],
                                                    depth=6 * units.km)

# Wind mean is the U and v component of sfc-6km mean flow
right, left, wind_mean = mpcalc.bunkers_storm_motion(pres_trimmed, u_trimmed1, v_trimmed1, height_trimmed1)

Errors, Traceback, and Logs

ValueError                                Traceback (most recent call last)
Input In [14], in <cell line: 398>()
    393 strShear = str(rounded_bulk_shear)
    395 #***Bunkers Storm Motion***
    396 # Gets u and v components for each type of bunkers storm motion
    397 # Wind mean is the U and v component of sfc-6km mean flow
--> 398 right, left, wind_mean = mpcalc.bunkers_storm_motion(pres_trimmed, u_trimmed1, v_trimmed1, height_trimmed1)
    400 # Extracts u and v components for each category
    401 uright = right[0]

File ~/miniconda3/lib/python3.9/site-packages/metpy/xarray.py:1235, in preprocess_and_wrap.<locals>.decorator.<locals>.wrapper(*args, **kwargs)
   1232     _mutate_arguments(bound_args, units.Quantity, lambda arg, _: arg.m)
   1234 # Evaluate inner calculation
-> 1235 result = func(*bound_args.args, **bound_args.kwargs)
   1237 # Wrap output based on match and match_unit
   1238 if match is None:

File ~/miniconda3/lib/python3.9/site-packages/metpy/units.py:298, in check_units.<locals>.dec.<locals>.wrapper(*args, **kwargs)
    295 @functools.wraps(func)
    296 def wrapper(*args, **kwargs):
    297     _check_units_inner_helper(func, sig, defaults, dims, *args, **kwargs)
--> 298     return func(*args, **kwargs)

File ~/miniconda3/lib/python3.9/site-packages/metpy/calc/indices.py:195, in bunkers_storm_motion(pressure, u, v, height)
    155 r"""Calculate the Bunkers right-mover and left-mover storm motions and sfc-6km mean flow.
    156 
    157 Uses the storm motion calculation from [Bunkers2000]_.
   (...)
    192 
    193 """
    194 # mean wind from sfc-6km
--> 195 _, u_mean, v_mean = get_layer(pressure, u, v, height=height,
    196                               depth=units.Quantity(6000, 'meter'))
    197 wind_mean = units.Quantity([np.mean(u_mean).m, np.mean(v_mean).m], u_mean.units)
    199 # mean wind from sfc-500m

File ~/miniconda3/lib/python3.9/site-packages/metpy/xarray.py:1235, in preprocess_and_wrap.<locals>.decorator.<locals>.wrapper(*args, **kwargs)
   1232     _mutate_arguments(bound_args, units.Quantity, lambda arg, _: arg.m)
   1234 # Evaluate inner calculation
-> 1235 result = func(*bound_args.args, **bound_args.kwargs)
   1237 # Wrap output based on match and match_unit
   1238 if match is None:

File ~/miniconda3/lib/python3.9/site-packages/metpy/units.py:298, in check_units.<locals>.dec.<locals>.wrapper(*args, **kwargs)
    295 @functools.wraps(func)
    296 def wrapper(*args, **kwargs):
    297     _check_units_inner_helper(func, sig, defaults, dims, *args, **kwargs)
--> 298     return func(*args, **kwargs)

File ~/miniconda3/lib/python3.9/site-packages/metpy/calc/tools.py:600, in get_layer(pressure, height, bottom, depth, interpolate, *args)
    597 else:
    598     raise ValueError('Depth must be specified in units of length or pressure')
--> 600 top_pressure, _ = _get_bound_pressure_height(pressure, top, height=height,
    601                                              interpolate=interpolate)
    603 ret = []  # returned data variables in layer
    605 # Ensure pressures are sorted in ascending order

File ~/miniconda3/lib/python3.9/site-packages/metpy/calc/tools.py:427, in _get_bound_pressure_height(pressure, bound, height, interpolate)
    424     raise ValueError('Specified bound is outside pressure range.')
    425 if height is not None and not (_less_or_close(bound_height, np.nanmax(height))
    426                                and _greater_or_close(bound_height, np.nanmin(height))):
--> 427     raise ValueError('Specified bound is outside height range.')
    429 return bound_pressure, bound_height

ValueError: Specified bound is outside height range.

[kylejgillett]

I think the bunkers calculation will find 0-6km on its own, so you shouldn't have to use 'trimmed' arrays. In my code I just use my base p, u, v, & z arrays.

[dopplershift]

@kylejgillett is correct, bunkers_storm_motion will take care of calculating all the layers necessary, so you should pass the full profiles you have--don't worry about trimming them.

I'm going to leave this open as a reminder to improve the docs to describe the method and explicitly call out that full profiles should be passed.