An objective method to associate local weather extremes with characteristic circulation structures

In this paper we give methods to find characteristic circulation patterns which are connected to local extreme temperature anomalies. Two data reduction techniques are applied: Legendre polynomial fitting and watershedding. For polynomial fitting a clear trend is found with respect to local temperatures. However, the trend is not distinctive enough to give clear answers on the type of circulation patterns belonging to local extremes. The main advantage of watershedding is that the physical properties of the circulation patterns are retained while the dimension of the data is largely reduced. Expert knowledge, however, is needed to model these main features as predictors