Ekman模型时间变化风应力系数的伴随参数估计

Based on the time-varying parameters, we used the adjoint assimilation method to invert the time-varying wind drag coefficients (WDCs) in the Ekman model. The method is testified by running twin experiments and practical experiments. In the twin experiments, the response of estimated WDCs to different influencing factors is studied, including: distributions of wind speed, distributions of WDCs, initial guess values, number of independent parameters, observation errors, and layers of observations. The results of twin experiments verified the effectiveness of the time-varying WDCs in the Ekman model. The results are followed. 1. The different distributions of WDCs can be successfully inverted under different wind speed distributions. 2. The inversion result is sensitive to the values of initial guess; therefore, the initial guess should be as reasonable as possible to improve the results and reduce the convergence time. 3. The selection of the number of the independent WDCs can significantly affect the inversion results. 4. The observation error can affect the inversion results, and reasonable inversion results can be obtained with maximum error below 20%. 5. The inversion results are more sensitive to the surface and subsurface observations, which is determined by the physical dynamics of the Ekman model. In practice, the observed Ekman current components are obtained from Bermuda Testbed Moorings by removing the periodic tidal components and the geostrophic components. Then the observed Ekman currents are assimilated into the model to invert the time-varying WDCs during the observation. By comparing the simulated with the observed velocities, we proved that the adjoint assimilation method could derive reasonable time-varying WDCs from measured data, which is a useful attempt to determine the WDCs for ocean models.