A Spatially Dependent Nudging Method and Its Application to a Global Tide Assimilation.

Tides represent a crucial dynamic process in the ocean and play a vital role in both marine and atmospheric studies; thus, accurate simulation of tidal processes is of the utmost importance in tidal circulation models. Based on the sequential data assimilation method and the concept of the Kalman gain matrix, this paper proposes a new nudging method with spatially dependent coefficients for tidal assimilation. The spatial-dependent nudging method not only retains the advantages of the traditional nudging method but also facilitates the direct determination of a more reasonable spatial distribution of nudging coefficients. Utilizing the M2 tidal constituent (the main lunar semidiurnal tide) as an illustration, we conducted assimilation experiments of sea-level data to the barotropic circulation and tide model to assess the global harmonic constants of the M2 constituent. The results demonstrate that the spatial-dependent nudging method successfully mitigates deviations of tidal phase lag. Following assimilation using the new method, the deviations of the M2 tidal amplitude and phase lag can be reduced by 47% and 18% compared to the traditional nudging method, respectively, while the respective values for the non-assimilated case are as much as 9% and 11%. We also applied the S-nudging method to realistic tidal simulations and noted a significantly enhanced effectiveness relative to traditional methods, making it highly valuable for modeling oceanic tidal circulations. [ABSTRACT FROM AUTHOR]