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Fix q_vector units w/ default static stability #3690

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Jan 6, 2025
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Fix q_vector units w/ default static stability #3690

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407eb0d
DOC: Improve q_vector documentation (Fixes #3689)
dopplershift Nov 13, 2024
5bebff4
DOC: Pass static_stability in QVector example
dopplershift Jan 2, 2025
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6 changes: 4 additions & 2 deletions examples/calculations/QVector.py
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Original file line number Diff line number Diff line change
Expand Up @@ -23,8 +23,10 @@
# Calculate the temperature advection of the flow
tadv = mpcalc.advection(ds.temperature, ds.uwind, ds.vwind)

# Calculate the q-vectors
u_qvect, v_qvect = mpcalc.q_vector(ds.uwind, ds.vwind, ds.temperature, 850 * units.hPa)
# Calculate the q-vectors. Passing in a fixed value of static stability, but could also
# use `mpcalc.static_stability()`.
u_qvect, v_qvect = mpcalc.q_vector(ds.uwind, ds.vwind, ds.temperature, 850 * units.hPa,
static_stability=0.02 * units('J / kg / Pa^2'))

# start figure and set axis
fig, ax = plt.subplots(figsize=(5, 5))
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9 changes: 8 additions & 1 deletion src/metpy/calc/kinematics.py
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Expand Up @@ -1275,7 +1275,8 @@ def inertial_advective_wind(
broadcast=('u', 'v', 'temperature', 'pressure', 'static_stability', 'parallel_scale',
'meridional_scale')
)
@check_units('[speed]', '[speed]', '[temperature]', '[pressure]', '[length]', '[length]')
@check_units('[speed]', '[speed]', '[temperature]', '[pressure]', '[length]', '[length]',
'[energy] / [mass] / [pressure]**2')
def q_vector(
u,
v,
Expand Down Expand Up @@ -1307,6 +1308,12 @@ def q_vector(
- 2 \nabla_p \cdot \vec{Q} -
\frac{R}{\sigma p} \beta \frac{\partial T}{\partial x}
By default, this function uses a unitless value of 1 for ``static_stability``, which
replicates the functionality of the GEMPAK ``QVEC`` function. If a value is given for
``static_stability``, it should have dimensionality of ``energy / mass / pressure^2``, and
will result in behavior that matches that of GEMPAK's ``QVCL`` function;
`static_stability` can be used to calculate this value if desired.
Parameters
----------
u : (..., M, N) `xarray.DataArray` or `pint.Quantity`
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