docs: def get_lon_variable(nc):
      '''
      Returns the variable for longitude
  
      :param netCDF4.Dataset nc: netCDF dataset
      '''
      if 'longitude' in nc.variables:
          return 'longitude'
      longitudes = nc.get_variables_by_attributes(standard_name="longitude")
      if longitudes:
          return longitudes[0].name
      return None