An empirical parameterization of subsurface entrainment temperature for improved SST anomaly simulations in an intermediate ocean model

An empirical model for the temperature of subsurface water entrained into the ocean mixed layer (T-e) 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 T-e from an SSTA equation using observed SST and simulated Upper-ocean currents. A relationship between T-e 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 T-e anomalies than other local schemes and quite realistically depicts interannual variability of T-e, including a nonlocal phase lag relation of T-e variations relative to SSH anomalies over the central equatorial Pacific. An improved T-e 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 T-e parameterization. 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 T-e model constructed from one historical period can be successfully used to improve SSTA simulations in another.