docs: def is_circumpolar(self, var):
          """
          Test if a variable is on a circumpolar grid
  
          Parameters
          ----------
          %(CFDecoder.is_triangular.parameters)s
  
          Returns
          -------
          %(CFDecoder.is_triangular.returns)s"""
          xcoord = self.get_x(var)
          return xcoord is not None and xcoord.ndim == 2