Abstract
In this study, water levels observed at tide stations in the Bohai Sea, Yellow Sea, and East China Sea during Typhoons 7203 and 8509 were assimilated into a numerical assimilation storm surge model combined with regularization technique to study the wind-stress drag coefficient. The Tikhonov regularization technique with different regularization parameters was tested during the assimilation. Using the regularization technique, the storm surge elevations were successfully simulated in the whole sea areas during Typhoons 7203 and 8509. The storm surge elevations calculated with the regularization technique and the elevations calculated with independent point method were separately compared with the observed data. Comparison results demonstrated that the former was closer to the observed data. The regularization technique had the best performance when the regularization parameter was 100. The spatial distribution of the inverted drag coefficient, storm surge elevations, and the wind fields during both typhoons were presented. Simulated results indicated that the change of drag coefficient is more significant in the coastal regions of the Bohai Sea and north of the Yellow Sea. Further analysis showed that the rising water elevation in the Bohai Sea is mostly attributed to the influence of onshore winds, and the negative storm surge in the South Yellow Sea is mainly caused by offshore winds.
Highlights
Abnormal sea level rise or fall associated with storm surge usually results from strong winds and atmospheric perturbations [1,2,3,4]
Lionello et al utilized the variational data assimilation method to forecast the storm surge in the north of Adriatic Sea, showing that the assimilation method can effectively improve the reliability of the storm surge forecast [13]
In the present study, by assimilating water levels observed at tide stations during Typhoons 7203 and 8509 into a storm surge model, we will optimize the drag coefficient in the Bohai Sea, Yellow Sea, and East China Sea using the Tikhonov regularization technique with different regularization parameters, and examine the spatially varying drag coefficient in these areas
Summary
Abnormal sea level rise or fall associated with storm surge usually results from strong winds and atmospheric perturbations [1,2,3,4]. To improve storm surge forecast, Li et al optimized the drag coefficient and initial condition using the three-dimensional numerical and adjoint ocean model, and their result demonstrated that simultaneously adjusting both of them can achieve much more improvements [18]. Xu et al investigated the impacts of tide-surge interactions on storm surges in the coast of the Bohai Sea, Yellow Sea, and East China Sea using a two-dimensional coupled tide-surge model It indicated that the tide-surge interactions should be considered when predicting storm surge levels [20]. In the present study, by assimilating water levels observed at tide stations during Typhoons 7203 and 8509 into a storm surge model, we will optimize the drag coefficient in the Bohai Sea, Yellow Sea, and East China Sea using the Tikhonov regularization technique with different regularization parameters, and examine the spatially varying drag coefficient in these areas. The spatially varying wind stress drag coefficient with wind speed is obtained by the regularization method, providing the service for the accurate simulation and prediction of storm surges
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