我正试图按照这个训练示例来计算NCEP/NCAR数据上的QGω，但我被mpcalc.conversion((所困扰。
看起来好像我的dx和dy变量是不同的形状，但我直接遵循了一个在线示例中的例程，这个示例应该是有效的。
import numpy as np
import xarray as xr
import metpy.calc as mc
import metpy.constants as mpconstants
from metpy.units import units
# CONSTANTS
# ---------
sigma = 2.0e-6 * units('m^2 Pa^-2 s^-2')
f0 = 1e-4 * units('s^-1')
Rd = mpconstants.Rd
path = './'
uf = 'uwnd.2018.nc'
vf = 'vwnd.2018.nc'
af = 'air.2018.nc'
ads = xr.open_dataset(path+af).metpy.parse_cf()
uds = xr.open_dataset(path+uf).metpy.parse_cf()
vds = xr.open_dataset(path+vf).metpy.parse_cf()
a700 = ads['air'].metpy.sel(
level=700 * units.hPa,
time='2018-01-04T12')
u700 = uds['uwnd'].metpy.sel(
level=700 * units.hPa,
time='2018-01-04T12')
v700 = vds['vwnd'].metpy.sel(
level=700 * units.hPa,
time='2018-01-04T12')
lats = ads['lat'].metpy.unit_array
lons = ads['lon'].metpy.unit_array
X, Y = np.meshgrid(lons,lats)
dx, dy = mc.lat_lon_grid_deltas(lons,lats)
avort = mc.absolute_vorticity(u700, v700,
dx, dy, lats[:,None])
print('Array shape:', avort.shape)
print('DX shape:', dx.shape)
print('DY shape:', dy.shape)
print('U700 shape:', u700.shape)
print('V700 shape:', v700.shape)
vortadv = mc.advection(avort, (u700,v700), (dx,dy)).to_base_units()
这是错误消息，看起来我可能有单元问题？
Found lat/lon values, assuming latitude_longitude for projection grid_mapping variable
Found lat/lon values, assuming latitude_longitude for projection grid_mapping variable
Found lat/lon values, assuming latitude_longitude for projection grid_mapping variable
/work1/jsa/anconda3/envs/earth/lib/python3.7/site-packages/metpy/calc/basic.py:1033: UserWarning: Input over 1.5707963267948966 radians. Ensure proper units are given.
'Ensure proper units are given.'.format(max_radians))
/work1/jsa/anconda3/envs/earth/lib/python3.7/site-packages/pint/quantity.py:888: RuntimeWarning: invalid value encountered in true_divide
magnitude = magnitude_op(new_self._magnitude, other._magnitude)
Array shape: (73, 144)
DX shape: (73, 143)
DY shape: (72, 144)
U700 shape: (73, 144)
V700 shape: (73, 144)
Traceback (most recent call last):
File "metpy.decomp.py", line 56, in <module>
vortadv = mc.advection(avort, (u700,v700), (dx,dy)).to_base_units()
File "/work1/jsa/anconda3/envs/earth/lib/python3.7/site-packages/metpy/xarray.py", line 570, in wrapper
return func(*args, **kwargs)
File "/work1/jsa/anconda3/envs/earth/lib/python3.7/site-packages/metpy/calc/kinematics.py", line 61, in wrapper
ret = func(*args, **kwargs)
File "/work1/jsa/anconda3/envs/earth/lib/python3.7/site-packages/metpy/calc/kinematics.py", line 320, in advection
wind = _stack(wind)
File "/work1/jsa/anconda3/envs/earth/lib/python3.7/site-packages/metpy/calc/kinematics.py", line 24, in _stack
return concatenate([a[np.newaxis] if iterable(a) else a for a in arrs], axis=0)
File "/work1/jsa/anconda3/envs/earth/lib/python3.7/site-packages/metpy/calc/kinematics.py", line 24, in <listcomp>
return concatenate([a[np.newaxis] if iterable(a) else a for a in arrs], axis=0)
File "/work1/jsa/anconda3/envs/earth/lib/python3.7/site-packages/xarray/core/dataarray.py", line 642, in __getitem__
return self.isel(indexers=self._item_key_to_dict(key))
File "/work1/jsa/anconda3/envs/earth/lib/python3.7/site-packages/xarray/core/dataarray.py", line 1040, in isel
indexers, drop=drop, missing_dims=missing_dims
File "/work1/jsa/anconda3/envs/earth/lib/python3.7/site-packages/xarray/core/dataset.py", line 2014, in _isel_fancy
name, var, self.indexes[name], var_indexers
File "/work1/jsa/anconda3/envs/earth/lib/python3.7/site-packages/xarray/core/indexes.py", line 106, in isel_variable_and_index
new_variable = variable.isel(indexers)
File "/work1/jsa/anconda3/envs/earth/lib/python3.7/site-packages/xarray/core/variable.py", line 1118, in isel
return self[key]
File "/work1/jsa/anconda3/envs/earth/lib/python3.7/site-packages/xarray/core/variable.py", line 766, in __getitem__
dims, indexer, new_order = self._broadcast_indexes(key)
File "/work1/jsa/anconda3/envs/earth/lib/python3.7/site-packages/xarray/core/variable.py", line 612, in _broadcast_indexes
return self._broadcast_indexes_outer(key)
File "/work1/jsa/anconda3/envs/earth/lib/python3.7/site-packages/xarray/core/variable.py", line 688, in _broadcast_indexes_outer
return dims, OuterIndexer(tuple(new_key)), None
File "/work1/jsa/anconda3/envs/earth/lib/python3.7/site-packages/xarray/core/indexing.py", line 410, in __init__
f"invalid indexer array, does not have integer dtype: {k!r}"
TypeError: invalid indexer array, does not have integer dtype: array(None, dtype=object)
提前感谢您的帮助！
所以问题是在MetPy 1.0中，为了更容易使用，advection的签名更改为advection(scalar, u, v)。此外，由于您使用MetPy 1.0处理Xarray数据，它可以为您处理所有坐标数据——您甚至不需要手动处理dx和dy：
subset = dict(level=700 * units.hPa, time='2018-01-04T12')
a700 = ads['air'].metpy.sel(**subset)
u700 = uds['uwnd'].metpy.sel(**subset)
v700 = vds['vwnd'].metpy.sel(**subset)
avort = mc.absolute_vorticity(u700, v700)
vortadv = mc.advection(avort, u700, v700).to_base_units()
我们需要更新这个训练示例，但现在我建议查看画廊示例500百帕位势高度、绝对涡度、风和500百帕涡平流。