Origins of coupled-model biases in the Arabian-Sea climatological state

Origins of coupled-model biases in the Arabian-Sea climatological state AbstractIn this study, we investigate biases of the climatological mean state of the northern Arabian Sea (NAS) in 31 coupled ocean-atmosphere models. Our focus is to understand the cause of the large biases in the depth of the 20°C isotherm (△D20) that occur in many of them. Other prominent biases are: the depth (hPG) and temperature (TPG) of Persian-Gulf water (PGW); and the wintertime mixed-layer thickness (MLT) along the northern boundary.For models that lack a Persian Gulf (Group 1), △D20 is determined by the wintertime MLT bias (△MLT) through the formation of an Arabian-Sea high-salinity water mass (ASHSW) that is too deep. For models with a Persian Gulf (Group 2), if hPG > MLT (Group 2B), PGW remains mostly trapped to the western boundary and, again, △MLT directly controls △D20. If hPG ≲ MLT (Group 2A), PGW spreads into the NAS and impacts △D20 because TPG > 20°C; nevertheless △MLT still influences △D20 indirectly through its impact on hPG.The thick, wintertime mixed layer is driven primarily by surface cooling Q during the fall. Nevertheless, variations in △MLT among the models are more strongly linked to biases in the density stratification (jump) across the bottom of the mixed layer than to Q biases. The jump is in turn determined primarily by sea-surface-salinity biases (△SSS) advected into the NAS by the West India Coastal Current, and the source of △SSS is the rainfall deficit associated with the models’ weak, summer-monsoon. Ultimately, then, △D20 is linked to this deficit. http://www.deepdyve.com/assets/images/DeepDyve-Logo-lg.png Journal of Climate American Meteorological Society

Origins of coupled-model biases in the Arabian-Sea climatological state

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Publisher
American Meteorological Society
Copyright
Copyright © American Meteorological Society
ISSN
1520-0442
D.O.I.
10.1175/JCLI-D-17-0417.1
Publisher site
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Abstract

AbstractIn this study, we investigate biases of the climatological mean state of the northern Arabian Sea (NAS) in 31 coupled ocean-atmosphere models. Our focus is to understand the cause of the large biases in the depth of the 20°C isotherm (△D20) that occur in many of them. Other prominent biases are: the depth (hPG) and temperature (TPG) of Persian-Gulf water (PGW); and the wintertime mixed-layer thickness (MLT) along the northern boundary.For models that lack a Persian Gulf (Group 1), △D20 is determined by the wintertime MLT bias (△MLT) through the formation of an Arabian-Sea high-salinity water mass (ASHSW) that is too deep. For models with a Persian Gulf (Group 2), if hPG > MLT (Group 2B), PGW remains mostly trapped to the western boundary and, again, △MLT directly controls △D20. If hPG ≲ MLT (Group 2A), PGW spreads into the NAS and impacts △D20 because TPG > 20°C; nevertheless △MLT still influences △D20 indirectly through its impact on hPG.The thick, wintertime mixed layer is driven primarily by surface cooling Q during the fall. Nevertheless, variations in △MLT among the models are more strongly linked to biases in the density stratification (jump) across the bottom of the mixed layer than to Q biases. The jump is in turn determined primarily by sea-surface-salinity biases (△SSS) advected into the NAS by the West India Coastal Current, and the source of △SSS is the rainfall deficit associated with the models’ weak, summer-monsoon. Ultimately, then, △D20 is linked to this deficit.

Journal

Journal of ClimateAmerican Meteorological Society

Published: Dec 15, 2017

References

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