截面分析问题

Question

我正尝试按照 Metpy 网站上的示例代码对网格数据集执行横截面分析。

首先，我可以使用 xarray 读取原始的 grib2 数据集，也可以在将其转换为 netCDF 格式后读取。

我成功导入了所有需要的包：

import cartopy.crs as ccrs
import cartopy.feature as cfeature
import matplotlib.pyplot as plt
import numpy as np
import xarray as xr

import metpy.calc as mpcalc
from metpy.interpolate import cross_section

然后，我确保可以使用以下命令读取文件：

data = xr.open_dataset('/home/rik/hrrr/gtgn/gtgn.t2215z.edr.f000.nc', False)
print(data)
<xarray.Dataset>
Dimensions:            (alt: 52, time: 1, x: 451, y: 337)
Coordinates:
  * time               (time) datetime64[ns] 2020-06-18T22:15:00
  * x                  (x) float64 0.0 1.355e+04 ... 6.082e+06 6.095e+06
  * y                  (y) float64 0.0 1.355e+04 ... 4.538e+06 4.551e+06
  * alt                (alt) float64 0.0 30.0 304.0 ... 1.494e+04 1.524e+04
Data variables:
    Lambert_Conformal  int32 ...
    param30.19.0       (time, alt, y, x) float32 ...
Attributes:
    CDI:          Climate Data Interface version 1.9.8 (https://mpimet.mpg.de...
    Conventions:  CF-1.6
    history:      Wed Oct 07 17:19:41 2020: cdo -f nc copy gtgn.t2215z.edr.f0...
    institution:  National Center for Atmospheric Research
    CDO:          Climate Data Operators version 1.9.8 (https://mpimet.mpg.de...

添加 MetPy 的 CF 解析命令给我以下 ValueError：

data = xr.open_dataset('/home/rik/hrrr/gtgn/gtgn.t2215z.edr.f000.nc')
data = data.metpy.parse_cf().squeeze()
print(data)
---------------------------------------------------------------------------
ValueError                                Traceback (most recent call last)
<ipython-input-3-fa63435fbf07> in <module>
      1 data = xr.open_dataset('/home/rik/hrrr/gtgn/gtgn.t2215z.edr.f000.nc')
----> 2 data = data.metpy.parse_cf().squeeze()
      3 print(data)

~/miniconda3/envs/metpy/lib/python3.7/site-packages/metpy/xarray.py in parse_cf(self, varname, coordinates)
    510         """
    511         from .cbook import iterable
--> 512         from .plots.mapping import CFProjection
    513 
    514         if varname is None:

~/miniconda3/envs/metpy/lib/python3.7/site-packages/metpy/plots/__init__.py in <module>
     25                 convert_gempak_color])  # pylint: disable=undefined-variable
     26 try:
---> 27     from .cartopy_utils import USCOUNTIES, USSTATES
     28     __all__.extend([USCOUNTIES, USSTATES])
     29 except ImportError:

~/miniconda3/envs/metpy/lib/python3.7/site-packages/metpy/plots/cartopy_utils.py in <module>
     41 
     42 
---> 43 USCOUNTIES = MetPyMapFeature('us_counties', '20m', facecolor='None', edgecolor='black')
     44 
     45 USSTATES = MetPyMapFeature('us_states', '20m', facecolor='None', edgecolor='black')

~/miniconda3/envs/metpy/lib/python3.7/site-packages/metpy/plots/cartopy_utils.py in __init__(self, name, scale, **kwargs)
     14     def __init__(self, name, scale, **kwargs):
     15         """Create USCountiesFeature instance."""
---> 16         super().__init__('', name, scale, **kwargs)
     17 
     18     def geometries(self):

~/miniconda3/envs/metpy/lib/python3.7/site-packages/cartopy/feature/__init__.py in __init__(self, category, name, scale, **kwargs)
    262         self.scaler = scale
    263         # Make sure this is a valid resolution
--> 264         self._validate_scale()
    265 
    266     @property

~/miniconda3/envs/metpy/lib/python3.7/site-packages/cartopy/feature/__init__.py in _validate_scale(self)
    272             raise ValueError(
    273                 '{} is not a valid Natural Earth scale. '.format(self.scale) +
--> 274                 'Valid scales are "110m", "50m", and "10m".'
    275             )
    276 

ValueError: 20m is not a valid Natural Earth scale. Valid scales are "110m", "50m", and "10m".

我正在使用 Metpy v0.12.1 和 xarray v0.15.1

而且，有趣的是，当我重新运行相同的代码时，我收到了另一条错误消息： NameError: name 'ctables' is not defined

请指教解析数据时出了什么问题。

Answer 1

get_test_data() 仅适用于使用 MetPy 的 built-in 测试数据集之一。使用您自己的数据时，您应该省略调用此函数，因此使用 open_dataset 的代码应如下所示：

data = xr.open_dataset('/home/rik/hrrr/gtgn/gtgn.t2215z.edr.f000.nc')

截面分析问题

Cross Section Analysis Issue

metpy