Temporal variability of vertical nontidal circulation pattern in a partially mixed estuary: Comparison of self‐organizing map and empirical orthogonal functions

On the basis of a 233‐day moored acoustic Doppler current profiler data set in an estuarine strait, temporal variability of vertical estuarine circulation is examined using self‐organizing map (SOM) and empirical orthogonal functions (EOF). The SOM identifies a continuum of patterns of which eight have been selected. The best matching unit (BMU) time series shows distinct seasonal variation which separates the data set into three seasonal segments. Also, monthly variation can be discerned by BMU sequences, and the data set is further separated into seven monthly segments. The EOF analysis of the whole record identifies only four patterns which are contained in the SOM patterns. However, EOF analysis of the seven monthly segments shows distinct monthly variation of the first two EOF modes. Moreover, those EOF modes are compatible with the SOM patterns showing consistency between the two techniques. The synoptic variability is described by four selected events which correspond to particular BMU sequences and represent filling and draining processes. The pattern‐forcing relationships are explored with EOF principle components. Long‐term variations of circulation patterns are dominated by river discharge and winds. Short‐term variations explored within seasonal and monthly segments indicate that the flow patterns are results of combined effect of forcing. Officer's (1976) analytical solutions of estuarine circulation are applied, and the results support the flow patterns and pattern‐forcing relationship revealed by SOM and EOF analysis.