North and equatorial Pacific Ocean circulation in the CORE-II hindcast simulations

Abstract

We evaluate the mean circulation patterns, water mass distributions, and tropical dynamics of the North and Equatorial Pacific Ocean based on a suite of global ocean-sea ice simulations driven by the CORE-II atmospheric forcing from 1963-2007. The first three moments (mean, standard deviation and skewness) of sea surface height and surface temperature variability are assessed against observations. Large discrepancies are found in the variance and skewness of sea surface height and in the skewness of sea surface temperature. Comparing with the observation, most models underestimate the Kuroshio transport in the Asian Marginal seas due to the missing influence of the unresolved western boundary current and meso-scale eddies. In terms of the Mixed Layer Depths (MLDs) in the North Pacific, the two observed maxima associated with Subtropical Mode Water and Central Mode Water formation coalesce into a large pool of deep MLDs in all participating models, but another local maximum associated with the formation of Eastern Subtropical Mode Water can be found in all models with different magnitudes. The main model bias of deep MLDs results from excessive Subtropical Mode Water formation due to inaccurate representation of the Kuroshio separation and of the associated excessively warm and salty Kuroshio water. Further water mass analysis shows that the North Pacific Intermediate Water can penetrate southward in most models, but its distribution greatly varies among models depending not only on grid resolution and vertical coordinate but also on the model dynamics. All simulations show overall similar large scale tropical current system, but with differences in the structures of the Equatorial Undercurrent.

Sensitivity of Coupled Tropical Pacific Model Biases to Convective Parameterization in CESM1

“…The wind stress curl and consequently the NECC are both present in SODA. However, the CORE data set, which is used to force the OCN simulation does not accurately represent the positive wind stress curl along 10°N (Tseng et al, ). As a result, the thermocline ridge and NECC are poorly simulated in the OCN simulation (supporting information Figure S6).…”

Mechanisms Driving the Interannual Variability of the Bering Strait Throughflow

“…The model employs a climatology of the monthly mean river runoff provided by Dai et al (). Previous research showed that FESOM with CORE‐II forcing can reasonably simulate sea ice and ocean in the Arctic and North Pacific Oceans compared to observations and other models (e.g., Ilıcak et al, ; Tseng et al, ; Wang et al, , ).…”

“…The model employs a climatology of the monthly mean river runoff provided by Dai et al (2009). Previous research showed that FESOM with CORE-II forcing can reasonably simulate sea ice and ocean in the Arctic and North Pacific Oceans compared to observations and other models (e.g., Ilıcak et al, 2016;Tseng et al, 2016;Wang et al, 2016aWang et al, , 2016b. A historical simulation (hereinafter referred to as "control") was carried out using the interannually varying forcing (IAVF) of the CORE-II data sets.…”

The Modeling of the North Equatorial Countercurrent in the Community Earth System Model and its Oceanic Component

“…It has been found that the NECC is not well simulated in many ocean models partly because of these complex dynamics (e.g., Grima et al, ; Philander et al, ; Tseng et al, ; Wu et al, ). In the recent second phase of the Coordinated Ocean‐ice Reference Experiments (CORE‐II), the NECC simulated in the stand‐alone ocean models generally tend to be weak (Tseng et al, , their Figure 19). The climatological mean zonal current speeds of the NECC from 15 different ocean models are all less than half of the observational estimate of 0.4 m/s (Johnson et al, ) at 220°E.…”

“…Even the high‐resolution KIEL model shows similar weak velocity magnitude. Although Tseng et al () identified the systematic model biases from the CORE‐II models and found that the systematic error may come mainly from the surface wind stress curl in the tropic, they did not further investigate the fundamental causes.…”