The accuracy of surface elevations in forward global barotropic and baroclinic tide models
This paper examines the accuracy of surface elevations in a forward global numerical model of 10 tidal constituents. Both one-layer and two-layer simulations are performed. As far as the authors are aware, the two-layer simulations and the simulations in a companion paper (Deep-Sea Research II, 51 (...
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ftumdeepblue:oai:deepblue.lib.umich.edu:2027.42/84338 2023-05-15T14:03:55+02:00 The accuracy of surface elevations in forward global barotropic and baroclinic tide models Arbic, Brian K. Garner, Steve Hallberg, Robert Simmons, Harper Geological Sciences, Department of Ann Arbor 2004 http://hdl.handle.net/2027.42/84338 en_US eng Elsevier Arbic, B.K., Garner, S.T., Hallberg, R.W., and H.L. Simmons 2004, The accuracy of surface elevations in forward global barotropic and baroclinic tide models, Deep-Sea Research II 51, 3069-3101, doi:10.1016/j.dsr2.2004.09.014 <http://hdl.handle.net/2027.42/84338> http://hdl.handle.net/2027.42/84338 15565143 Deep-Sea Research II Article 2004 ftumdeepblue https://doi.org/10.1016/j.dsr2.2004.09.014 2018-04-02T07:30:01Z This paper examines the accuracy of surface elevations in a forward global numerical model of 10 tidal constituents. Both one-layer and two-layer simulations are performed. As far as the authors are aware, the two-layer simulations and the simulations in a companion paper (Deep-Sea Research II, 51 (2004) 3043) represent the first published global numerical solutions for baroclinic tides. Self-consistent forward solutions for the global tide are achieved with a convergent iteration procedure for the self-attraction and loading term. Energies are too large, and elevation accuracies are poor, unless substantial abyssal drag is present. Reasonably accurate tidal elevations can be obtained with a spatially uniform bulk drag cd or horizontal viscosity KH; but only if these are inordinately large. More plausible schemes concentrate drag over rough topography. The topographic drag scheme used here is based on an exact analytical solution for arbitrary small-amplitude terrain, and supplemented by dimensional analysis to account for drag due to flow-splitting and low-level turbulence as well as that due to breaking of radiating waves. The scheme is augmented by a multiplicative factor tuned to minimize elevation discrepancies with respect to the TOPEX/ POSEIDON (T/P)-constrained GOT99.2 model. The multiplicative factor may account for undersampled small spatial scales in bathymetric datasets. An optimally tuned multi-constituent one-layer simulation has an RMS elevation discrepancy of 9.54 cm with respect to GOT99.2, in waters deeper than 1000m and over latitudes covered by T/P (66 N to 66 S). The surface elevation discrepancy decreases to 8.90 cm (92 percent of the height variance captured) in the optimally tuned two-layer solution. The improvement in accuracy is not due to the direct surface elevation signature of internal tides, which is of small amplitude, but to a shift in the barotropic tide induced by baroclinicity. Elevations are also more accurate in the two-layer model when pelagic tide gauges are used as the benchmark, and when the T/Pconstrained TPXO6.2 model is used as a benchmark in deep waters south of 66 S. For Antarctic diurnal tides, the improvement in forward model elevation accuracy with baroclinicity is substantial. The optimal multiplicative factor in the two-layer case is nearly the same as in the one-layer case, against initial expectations that the explicit resolution of low-mode conversion would allow less parameterized drag. In the optimally tuned two-layer M2 solution, local values of the ratio of temporally averaged squared upper layer speed to squared lower layer speed often exceed 10. Article in Journal/Newspaper Antarc* Antarctic University of Michigan: Deep Blue Antarctic Deep Sea Research Part II: Topical Studies in Oceanography 51 25-26 3069 3101 |
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Open Polar |
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University of Michigan: Deep Blue |
op_collection_id |
ftumdeepblue |
language |
English |
description |
This paper examines the accuracy of surface elevations in a forward global numerical model of 10 tidal constituents. Both one-layer and two-layer simulations are performed. As far as the authors are aware, the two-layer simulations and the simulations in a companion paper (Deep-Sea Research II, 51 (2004) 3043) represent the first published global numerical solutions for baroclinic tides. Self-consistent forward solutions for the global tide are achieved with a convergent iteration procedure for the self-attraction and loading term. Energies are too large, and elevation accuracies are poor, unless substantial abyssal drag is present. Reasonably accurate tidal elevations can be obtained with a spatially uniform bulk drag cd or horizontal viscosity KH; but only if these are inordinately large. More plausible schemes concentrate drag over rough topography. The topographic drag scheme used here is based on an exact analytical solution for arbitrary small-amplitude terrain, and supplemented by dimensional analysis to account for drag due to flow-splitting and low-level turbulence as well as that due to breaking of radiating waves. The scheme is augmented by a multiplicative factor tuned to minimize elevation discrepancies with respect to the TOPEX/ POSEIDON (T/P)-constrained GOT99.2 model. The multiplicative factor may account for undersampled small spatial scales in bathymetric datasets. An optimally tuned multi-constituent one-layer simulation has an RMS elevation discrepancy of 9.54 cm with respect to GOT99.2, in waters deeper than 1000m and over latitudes covered by T/P (66 N to 66 S). The surface elevation discrepancy decreases to 8.90 cm (92 percent of the height variance captured) in the optimally tuned two-layer solution. The improvement in accuracy is not due to the direct surface elevation signature of internal tides, which is of small amplitude, but to a shift in the barotropic tide induced by baroclinicity. Elevations are also more accurate in the two-layer model when pelagic tide gauges are used as the benchmark, and when the T/Pconstrained TPXO6.2 model is used as a benchmark in deep waters south of 66 S. For Antarctic diurnal tides, the improvement in forward model elevation accuracy with baroclinicity is substantial. The optimal multiplicative factor in the two-layer case is nearly the same as in the one-layer case, against initial expectations that the explicit resolution of low-mode conversion would allow less parameterized drag. In the optimally tuned two-layer M2 solution, local values of the ratio of temporally averaged squared upper layer speed to squared lower layer speed often exceed 10. |
author2 |
Geological Sciences, Department of Ann Arbor |
format |
Article in Journal/Newspaper |
author |
Arbic, Brian K. Garner, Steve Hallberg, Robert Simmons, Harper |
spellingShingle |
Arbic, Brian K. Garner, Steve Hallberg, Robert Simmons, Harper The accuracy of surface elevations in forward global barotropic and baroclinic tide models |
author_facet |
Arbic, Brian K. Garner, Steve Hallberg, Robert Simmons, Harper |
author_sort |
Arbic, Brian K. |
title |
The accuracy of surface elevations in forward global barotropic and baroclinic tide models |
title_short |
The accuracy of surface elevations in forward global barotropic and baroclinic tide models |
title_full |
The accuracy of surface elevations in forward global barotropic and baroclinic tide models |
title_fullStr |
The accuracy of surface elevations in forward global barotropic and baroclinic tide models |
title_full_unstemmed |
The accuracy of surface elevations in forward global barotropic and baroclinic tide models |
title_sort |
accuracy of surface elevations in forward global barotropic and baroclinic tide models |
publisher |
Elsevier |
publishDate |
2004 |
url |
http://hdl.handle.net/2027.42/84338 |
geographic |
Antarctic |
geographic_facet |
Antarctic |
genre |
Antarc* Antarctic |
genre_facet |
Antarc* Antarctic |
op_relation |
Arbic, B.K., Garner, S.T., Hallberg, R.W., and H.L. Simmons 2004, The accuracy of surface elevations in forward global barotropic and baroclinic tide models, Deep-Sea Research II 51, 3069-3101, doi:10.1016/j.dsr2.2004.09.014 <http://hdl.handle.net/2027.42/84338> http://hdl.handle.net/2027.42/84338 15565143 Deep-Sea Research II |
op_doi |
https://doi.org/10.1016/j.dsr2.2004.09.014 |
container_title |
Deep Sea Research Part II: Topical Studies in Oceanography |
container_volume |
51 |
container_issue |
25-26 |
container_start_page |
3069 |
op_container_end_page |
3101 |
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1766274818543452160 |