Reducing Phase and Amplitude Errors in Restoring Boundary Conditions

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  • 1 Climate Research Division Scripps Institution of Oceanography, La Jolla, California
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Abstract

Restoring boundary conditions are often used to drive ocean general circulation models. As typically such conditions impose time lags and amplitude errors in the seasonal cycle of the model surface tracer fields. Restoring boundary conditions also damp out the high-frequency components of the forcing with more damping for higher frequencies; thus, models using such conditions systematically underrepresent high-frequency variability in the surface tracer fields. A solution to these problems is presented for use when the forcing field is known beforehand. It is shown that this new formulation significantly reduces the time lags associated with the traditional form of restoring boundary conditions and improves the model's representation of surface variability. The new condition has no run-time overhead and does not impose any additional restrictions on the ability of the model to deviate from observations. The results of using the new boundary condition in an oceanic general circulation model are shown for cases with both monthly and weekly forcing.

Abstract

Restoring boundary conditions are often used to drive ocean general circulation models. As typically such conditions impose time lags and amplitude errors in the seasonal cycle of the model surface tracer fields. Restoring boundary conditions also damp out the high-frequency components of the forcing with more damping for higher frequencies; thus, models using such conditions systematically underrepresent high-frequency variability in the surface tracer fields. A solution to these problems is presented for use when the forcing field is known beforehand. It is shown that this new formulation significantly reduces the time lags associated with the traditional form of restoring boundary conditions and improves the model's representation of surface variability. The new condition has no run-time overhead and does not impose any additional restrictions on the ability of the model to deviate from observations. The results of using the new boundary condition in an oceanic general circulation model are shown for cases with both monthly and weekly forcing.

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