Editorial Type:
Article
Article Type:
Research Article

An Empirical Parameterization of Subsurface Entrainment Temperature for Improved SST Anomaly Simulations in an Intermediate Ocean Model

Rong-Hua Zhang International Research Institute for Climate Prediction (IRI), The Earth Institute at Columbia University, Palisades, New York

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Richard Kleeman Courant Institute for Mathematical Studies, New York University, New York, New York

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Stephen E. Zebiak International Research Institute for Climate Prediction (IRI), The Earth Institute at Columbia University, Palisades, New York

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Noel Keenlyside Max-Planck-Institut für Meteorologie, Hamburg, Germany

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Stephane Raynaud Courant Institute for Mathematical Studies, New York University, New York, New York

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Print Publication:
15 Jan 2005
DOI:
https://doi.org/10.1175/JCLI-3271.1
Page(s):
350–371
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Abstract

An empirical model for the temperature of subsurface water entrained into the ocean mixed layer (Te) is presented and evaluated to improve sea surface temperature anomaly (SSTA) simulations in an intermediate ocean model (IOM) of the tropical Pacific. An inverse modeling approach is adopted to estimate Te from an SSTA equation using observed SST and simulated upper-ocean currents. A relationship between Te and sea surface height (SSH) anomalies is then obtained by utilizing a singular value decomposition (SVD) of their covariance. This empirical scheme is able to better parameterize Te anomalies than other local schemes and quite realistically depicts interannual variability of Te, including a nonlocal phase lag relation of Te variations relative to SSH anomalies over the central equatorial Pacific. An improved Te parameterization naturally leads to better depiction of the subsurface effect on SST variability by the mean upwelling of subsurface temperature anomalies. As a result, SSTA simulations are significantly improved in the equatorial Pacific; a comparison with other schemes indicates that systematic errors of the simulated SSTAs are significantly small—apparently due to the optimized empirical Teparameterization. Cross validation and comparisons with other model simulations are made to illustrate the robustness and effectiveness of the scheme. In particular it is demonstrated that the empirical Te model constructed from one historical period can be successfully used to improve SSTA simulations in another.

* Current affiliation: Earth System Science Interdisciplinary Center, University of Maryland, College Park, College Park, Maryland

Corresponding author address: Rong-Hua Zhang, ESSIC, Computer and Space Science Bldg., No. 224, University of Maryland, College Park, College Park, MD 20742. Email: rzhang@essic.umd.edu

Abstract

An empirical model for the temperature of subsurface water entrained into the ocean mixed layer (Te) is presented and evaluated to improve sea surface temperature anomaly (SSTA) simulations in an intermediate ocean model (IOM) of the tropical Pacific. An inverse modeling approach is adopted to estimate Te from an SSTA equation using observed SST and simulated upper-ocean currents. A relationship between Te and sea surface height (SSH) anomalies is then obtained by utilizing a singular value decomposition (SVD) of their covariance. This empirical scheme is able to better parameterize Te anomalies than other local schemes and quite realistically depicts interannual variability of Te, including a nonlocal phase lag relation of Te variations relative to SSH anomalies over the central equatorial Pacific. An improved Te parameterization naturally leads to better depiction of the subsurface effect on SST variability by the mean upwelling of subsurface temperature anomalies. As a result, SSTA simulations are significantly improved in the equatorial Pacific; a comparison with other schemes indicates that systematic errors of the simulated SSTAs are significantly small—apparently due to the optimized empirical Teparameterization. Cross validation and comparisons with other model simulations are made to illustrate the robustness and effectiveness of the scheme. In particular it is demonstrated that the empirical Te model constructed from one historical period can be successfully used to improve SSTA simulations in another.

* Current affiliation: Earth System Science Interdisciplinary Center, University of Maryland, College Park, College Park, Maryland

Corresponding author address: Rong-Hua Zhang, ESSIC, Computer and Space Science Bldg., No. 224, University of Maryland, College Park, College Park, MD 20742. Email: rzhang@essic.umd.edu

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