NUMERICAL SIMULATION OF LOW-FREQUENCY WATER-LEVEL FLUCTUATION IN BOHAI SEA BASED ON ENSEMBLE KALMAN FILTER
The low-frequency fluctuation of water level at a subtidal scale caused by wind relaxation is a common marine dynamic process in the Bohai Sea and Yellow Sea in autumn and winter.It requires the numerical modelling to cover the entire Bohai Sea and Yellow Sea region and even the East China Sea to reproduce this phenomenon.As in the Bohai Sea model that taking the Bohai Strait as the open boundary,this modelling cannot be reproduced due to limited wind fetch.To solve this problem,we employed the ensemble kalman filter(ENKF)assimilation method,with which this phenomenon was successfully reproduced.Furthermore,the role of ENKF assimilation and its influencing factors was analyzed.It was found that the low-frequency fluctuation of water level in the Bohai Sea is driven by the water-levels at the open boundary.Using tidal data and wind data only could not reproduce the subtidal water level variation in the Bohai Sea.However,the low-frequency fluctuation of water level can be reproduced by the ENKF assimilation;and the assimilation result is better than the results driven sole by the open boundary forcings.The accuracy of ENKF assimilation is related to the number of ensembles and the location of sampling stations.Although more ensembles would lead to better assimilation results,over 40 ensembles could not improve the results significantly.The sampling stations selected should be evenly distributed in the Bohai Sea and kept far enough away from the boundary.
low frequency fluctuationdata assimilationensemble Kalman filteringBohai Seaopen boundary
万方数据
维普
