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Open boundary conditions for tidally and subtidally forced circulation in a limited‐area coastal model using the Regional Ocean Modeling System (ROMS)
Author(s) -
Liu Zhiqiang,
Gan Jianping
Publication year - 2016
Publication title -
journal of geophysical research: oceans
Language(s) - English
Resource type - Journals
eISSN - 2169-9291
pISSN - 2169-9275
DOI - 10.1002/2016jc011975
Subject(s) - forcing (mathematics) , geology , baroclinity , barotropic fluid , oceanography , flow (mathematics) , circulation (fluid dynamics) , tidal model , boundary (topology) , boundary current , spurious relationship , ocean current , climatology , computer science , mechanics , physics , mathematical analysis , mathematics , machine learning
In limited‐area ocean models, open boundary conditions (OBCs) often create dynamic inconsistencies and perform poorly in resolving tidal or subtidal flow when both forces exist. Orlanski‐type radiation OBCs are reasonably efficient at treating the subtidally forced flow, and Flather ‐type OBCs are commonly adapted for the tidally forced flow. However, neither of them performs well when tidal and subtidal forces simultaneously drive the flows. We have developed a novel OBC that integrates the active OBC in Gan and Allen (2005) and a Flather‐type OBC. This new OBC accommodates the concurrent Tidal and Subtidal (TST) forcing, and the respective tidal or subtidal forcing, at the open boundary of a limited‐area model. This new TST‐OBC treats the tidal component with a Flather‐type OBC, and it separates subtidal barotropic and baroclinic components into local (forced) and global (unforced) components. Then an unforced Orlanski‐type OBC can be applied to the global part. We applied the TST‐OBC to all model variables to reduce dynamic inconsistence. Using the Regional Ocean Modeling System, we applied the TST‐OBC to the shallow East China Sea shelf where strong tidal and subtidal forces over complex topography govern the circulation. Our numerical experiments and analyses suggest that the TST‐OBC was robust for both concurrent tidal‐subtidal forcing and solely tidal or subtidal forcing at the open boundary. It reduced spurious energy reflection, and, overall, it performed better than an Orlanski‐type or Flather‐type OBC in reproducing realistic tidal and subtidal shelf circulation.