基于卫星高度计资料同化的渤海和黄海M_2潮流数值模拟

Three-dimensional simulation of M_2 tidal current in Bohai and Yellow Seas by assimilating satellite altimetry

将基于数学物理反问题的四维变分同化技术应用到陆架浅海区正压潮流的三维数值模拟中.孪生实验结果表明,借助伴随同化技术,三维正压潮流模型的水位开边界条件可成功反演.实际实验同化从TOPEX/Poseidon高度计资料提取的潮汐调和常数,通过反演水位的第一边值开边界条件,数值模拟了渤海和黄海的M2潮汐潮流.同化后代价函数以及代价函数关于开边界Fourier系数的梯度的值均大幅度下降,证明了伴随同化方法的有效性.实验过程中潮流资料未参与同化,但由其表达的代价函数值仍然由1下降至0.09,表明从高度计数据反演陆架浅海区的潮流场具有高度的可行性.与其它工作相比,潮流模拟值与观测值之间的误差较小,所得同潮图及潮流椭圆分布图准确体现了渤海和黄海M2潮汐潮流的基本特征.本文工作表明伴随同化方法可有效提高潮流数值模拟的准确度.

The four-dimensional variational data assimilation technology based on inverse problem is applied to simulate the tidal currents in marginal shelf seas by assimilating satellite altimetry.The prescribed open boundary conditions of a three-dimensional barotropic tidal model are successfully inverted in the twin experiments.In the practical experiments,the open boundary conditions are optimized and the M2 tides and tidal currents in Bohai and Yellow Seas are simulated by assimilating tidal harmonic constants deduced from the TOPEX/Poseidon altimeter data.During the assimilation,the cost function and the gradients of cost function with respect to the open boundary conditions are decreased significantly.Although the current observations are not assimilated,the cost function in terms of current data is still decreased from 1 to 0.09,which demonstrates the feasibility of inverting tidal currents from satellite altimetry or other elevation measurements.The co-tidal charts and the near-surface M2 tidal current ellipses obtained in the practical experiment are in good agreement with the observed tides and tidal currents in the Bohai and Yellow Seas.This work indicates that the adjoint method can significantly improve the accuracy of three-dimensional simulation of tidal currents in the marginal shelf seas.