Yasumasa Miyazawa, Max Yaremchuk, Sergey M. Varlamov, Toru Miyama, Yu-Lin K. Chang, Hakase Hayashida
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An ensemble-based data assimilation system for forecasting variability of the Northwestern Pacific ocean
An adjoint-free four-dimensional variational (a4dVar) data assimilation (DA) is implemented in an operational ocean forecast system based on an eddy-resolving ocean general circulation model for the Northwestern Pacific. Validation of the system against independent observations demonstrates that fitting the model to time-dependent satellite altimetry during a 10-day DA window leads to substantial skill improvements in the succeeding 60-day hindcast. The a4dVar corrects representation of the Kuroshio path variation south of Japan by adjusting the dynamical balance between amplitude/wavelength of the meander and flow advection. A larger ensemble spread tends to reduce the skill in representing the observed sea surface height anomaly, suggesting that it is possible to use the ensemble information for quantifying the forecast error. The ensemble information is also utilized for modification of the background error covariance (BEC), which improves the accuracy of temperature and salinity distributions. The modified BEC yields the skill decline of the Kuroshio path variation during the 60-day hindcast period, and the ensemble sensitivity analysis shows that changes in the dynamical balance caused by the ensemble BEC result in such skill deterioration.
期刊介绍:
Ocean Dynamics is an international journal that aims to publish high-quality peer-reviewed articles in the following areas of research:
Theoretical oceanography (new theoretical concepts that further system understanding with a strong view to applicability for operational or monitoring purposes);
Computational oceanography (all aspects of ocean modeling and data analysis);
Observational oceanography (new techniques or systematic approaches in measuring oceanic variables, including all aspects of monitoring the state of the ocean);
Articles with an interdisciplinary character that encompass research in the fields of biological, chemical and physical oceanography are especially encouraged.