High latitude data assimilation study. RA-2

• Main Authors: Evensen, Geir, Hugen, V. J., Brusdal, K.
• Format: Report
• Language: English
• Published: Zenodo 2000
• Subjects: Nordic Seas; Atlantic; Ocean; Model; Data-assimilation; Altimetry; Ensemble Kalman Filter; Arctic Basin; North Atlantic
• Online Access: https://doi.org/10.5281/zenodo.7660700

The usefulness of high latitude altimeter data in a data assimilation system has been evalueted for the North Atlantic and the Nordic Seas. Within the project we have focused on reprocessing and gridding of high latitude altimeter data as well as the development and implementation of a sophisticated data assimilation method with a state of the art OGCM. The OGCM used is based on the Miami Isopycnic Coordinated Ocean Model (MICOM) which is a state of the art 3-dimensional ocean circulation model including thermodynamics and a mixed layer which interacts with atmospheric forcing fields. The assimilation scheme used is the Ensemble Kalman Filter (EnKF), which is a sophisticated method where proper evolution of error statistics is taken into account. The method has been particularly developed for use with highly nonlinear models with large state spaces and it is a natural choice for meeting the objectives in this particular project. The OGCM has been set up for the North Atlantic and the Nordic Seas on an orthogonal curvilinear grid, with enhanced resolution in the Gulf Stream extension and in the Nordic Seas. The model also includes the Arctic basin and has an ice model coupled to it. Thus, the model comprises a sophisticated system for modeling the circulation and climate in the North Atlantic and the Nordic Seas. A pilot assimilation experiment has been performed where altimeter data have been assimilated into MICOM using the EnKF. In this experiment we used a low resolution version of the model system for numerical efficiency. In addition to the assimilation of altimeter data we also implemented the possibility of assimilating sea surface temperature next phase of the project where the assimilation system is used with higher resolution to get a more realistic representation of the ocean circulation at the scales resolved by the altimeter data. Further, the possibility of real time operation of the system should be demonstrated. NERSC Technical Report no. 175. Funded by the European Space Agency, through ...