I downloaded Era5 U and V wind components from era-5 and I am using xarray to read the .nc file and select several lat lon points from the data. After i need to calculate wind speed and direction using metpy.calc function:
ds = xr.open_mfdataset('ERA5_u10_*.nc',combine='by_coords').metpy.parse_cf()
dv = xr.open_mfdataset('ERA5_v10_*.nc',combine='by_coords').metpy.parse_cf()
#direction =mpcalc.wind_direction(ds['u10'],dv['v10'])
#dd=mpcalc.wind_direction(ds.u10,dv.v10)
locations=[]
k=0
u10 = []
v10=[]
speed=[]
direction=[]
u100 = []
v100=[]
for i,j in zip(lats,lons):
stations_u=ds.sel(longitude=j,latitude=i,method='nearest')
stations_v=dv.sel(longitude=j,latitude=i,method='nearest')
u10.append(stations_u.u10)### mudar variavel
v10.append(stations_v.v10)### mudar variavel
speed.append(mpcalc.wind_speed(stations_u.u10,stations_v.v10))
direction.append(mpcalc.wind_direction(stations_u.u10,stations_v.v10))
Wind speed works with no problem, but wind direction raises an error:
runfile('/mnt/data1/ERA5/wind/untitled0.py', wdir='/mnt/data1/ERA5/wind')
Found valid latitude/longitude coordinates, assuming latitude_longitude for projection grid_mapping variable
Found valid latitude/longitude coordinates, assuming latitude_longitude for projection grid_mapping variable
Traceback (most recent call last):
File "/usr/local/python/anaconda3/envs/my_env/lib/python3.6/site-packages/dask/array/core.py", line 1615, in __setitem__
y = where(key, value, self)
File "/usr/local/python/anaconda3/envs/my_env/lib/python3.6/site-packages/dask/array/routines.py", line 1382, in where
return elemwise(np.where, condition, x, y)
File "/usr/local/python/anaconda3/envs/my_env/lib/python3.6/site-packages/dask/array/core.py", line 4204, in elemwise
broadcast_shapes(*shapes)
File "/usr/local/python/anaconda3/envs/my_env/lib/python3.6/site-packages/dask/array/core.py", line 4165, in broadcast_shapes
"shapes {0}".format(" ".join(map(str, shapes)))
ValueError: operands could not be broadcast together with shapes (262968,) (nan,) (262968,)
The above exception was the direct cause of the following exception:
Traceback (most recent call last):
File "/mnt/data1/ERA5/wind/untitled0.py", line 40, in <module>
direction.append(mpcalc.wind_direction(stations_u.u10,stations_v.v10))
File "/usr/local/python/anaconda3/envs/my_env/lib/python3.6/site-packages/metpy/xarray.py", line 1206, in wrapper
result = func(*bound_args.args, **bound_args.kwargs)
File "/usr/local/python/anaconda3/envs/my_env/lib/python3.6/site-packages/metpy/units.py", line 246, in wrapper
return func(*args, **kwargs)
File "/usr/local/python/anaconda3/envs/my_env/lib/python3.6/site-packages/metpy/calc/basic.py", line 104, in wind_direction
wdir[mask] += 360. * units.deg
File "/usr/local/python/anaconda3/envs/my_env/lib/python3.6/site-packages/pint/quantity.py", line 1868, in __setitem__
self._magnitude[key] = factor.magnitude
File "/usr/local/python/anaconda3/envs/my_env/lib/python3.6/site-packages/dask/array/core.py", line 1622, in __setitem__
) from e
ValueError: Boolean index assignment in Dask expects equally shaped arrays.
Example: da1[da2] = da3 where da1.shape == (4,), da2.shape == (4,) and da3.shape == (4,).
If i try to calculate Wdir with only 1 element in U and in V, surprisingly it works:
mpcalc.wind_direction(stations_u.u10[0],stations_v.v10[0]).values
Out[12]: array(173.41553, dtype=float32)
metpy.calc.wind_direction is unfortunately known not to work with Dask arrays--and in fact many places in MetPy don't work well with Dask, though we definitely want to. For now, to use wind_direction you'll need to turn stations_u, etc. into standard numpy arrays using e.g. .compute().