为什么xarray reftime键的末尾突然变成1？

我正在使用siphon从Unidata Thredds服务器下载GFS数据，因此可以使用MetPy对其进行绘制。我写了一个脚本来做到这一点，昨天效果很好：

#Get data using siphon
best_gfs = TDSCatalog('http://thredds.ucar.edu/thredds/catalog/grib/NCEP/GFS/Global_0p25deg/catalog.xml?dataset=grib/NCEP/GFS/Global_0p25deg/Best')
best_ds = best_gfs.datasets[0]
ncss = best_ds.subset()
query = ncss.query()
query.lonlat_box(north=55, south=20, east=-60, west=-120).time(datetime.utcnow())
query.accept('netcdf4')
query.variables('Geopotential_height_isobaric')

data = ncss.get_data(query)

#Parse data using MetPy
ds = xr.open_dataset(NetCDF4DataStore(data))
data = ds.metpy.parse_cf()

time_of_run = data['reftime'][0].dt.strftime('%Y%m%d_%H%MZ').values
print(time_of_run)

当我在美国东部时间下午2点运行时，此代码输出了2020-03-29 12：00Z，一切都很好。

当我今天早上运行它时，出现一个错误：

Traceback (most recent call last):
  File "C:\Users\jacks\Anaconda3\envs\metpy_test\lib\site-packages\xarray\core\dataset.py", line 1155, in _construct_dataarray
    variable = self._variables[name]
KeyError: 'reftime'

During handling of the above exception, another exception occurred:

Traceback (most recent call last):
  File "h5_rh_wind_gph_temp.py", line 51, in <module>
    time_of_run = data['reftime'][0].dt.strftime('%Y%m%d_%H%MZ').values
  File "C:\Users\jacks\Anaconda3\envs\metpy_test\lib\site-packages\xarray\core\dataset.py", line 1245, in __getitem__
    return self._construct_dataarray(key)
  File "C:\Users\jacks\Anaconda3\envs\metpy_test\lib\site-packages\xarray\core\dataset.py", line 1158, in _construct_dataarray
    self._variables, name, self._level_coords, self.dims
  File "C:\Users\jacks\Anaconda3\envs\metpy_test\lib\site-packages\xarray\core\dataset.py", line 165, in _get_virtual_variable
    ref_var = variables[ref_name]
KeyError: 'reftime'

这表明对“ reftime”键的引用无效。为了进行调查，我随后打印了“数据” xarray：

<xarray.Dataset>
Dimensions:                       (isobaric6: 34, lat: 141, lon: 241, time1: 1)
Coordinates:
    reftime1                      (time1) datetime64[ns] ...
  * time1                         (time1) datetime64[ns] 2020-03-30T12:00:00
  * isobaric6                     (isobaric6) float32 40.0 100.0 ... 100000.0
  * lat                           (lat) float32 55.0 54.75 54.5 ... 20.25 20.0
  * lon                           (lon) float32 240.0 240.25 ... 299.75 300.0
    crs                           object Projection: latitude_longitude
Data variables:
    Geopotential_height_isobaric  (time1, isobaric6, lat, lon) float32 ...
    LatLon_Projection             int32 ...
Attributes:
    Originating_or_generating_Center:                                        ...
    Originating_or_generating_Subcenter:                                     ...
    GRIB_table_version:                                                      ...
    Type_of_generating_process:                                              ...
    Analysis_or_forecast_generating_process_identifier_defined_by_originating...
    Conventions:                                                             ...
    history:                                                                 ...
    featureType:                                                             ...
    History:                                                                 ...
    geospatial_lat_min:                                                      ...
    geospatial_lat_max:                                                      ...
    geospatial_lon_min:                                                      ...
    geospatial_lon_max:                                                      ...

这表明我想要的信息（模型的运行时间）现在存储为“ reftime1”。为什么1突然出现在reftime键的末尾？它的出现有规律吗？我希望最终将这个脚本作为cron作业运行，以自动生成图，因此，最好能找到一种方法来预期名称的更改或完全避开键名。