Abstract
As salinity stratification is necessary to form the barrier layer (BL), the quantification of its role in BL interannual variability is crucial. This study assessed salinity variability and its effect on the BL in the equatorial Pacific using outputs from Beijing Normal University Earth System Model (BNU-ESM) simulations. A comparison between observations and the BNU-ESM simulations demonstrated that BNU-ESM has good capability in reproducing most of the interannual features observed in nature. Despite some discrepancies in both magnitude and location of the interannual variability centers, the displacements of sea surface salinity (SSS), barrier layer thickness (BLT), and SST simulated by BNU-ESM in the equatorial Pacific are realistic. During El Nino, for example, the modeled interannual anomalies of BLT, mixed layer depth, and isothermal layer depth, exhibit good correspondence with observations, including the development and decay of El Nino in the central Pacific, whereas the intensity of the interannual variabilities is weaker relative to observations. Due to the bias in salinity simulations, the SSS front extends farther west along the equator, whereas BLT variability is weaker in the central Pacific than in observations. Further, the BNU-ESM simulations were examined to assess the relative effects of salinity and temperature variability on BLT. Consistent with previous observation-based analyses, the interannual salinity variability can make a significant contribution to BLT relative to temperature in the western-central equatorial Pacific.
Highlights
It is well known that ENSO is Earth’s dominant source of interannual climate variability in the tropical Pacific
The salinity effects on ocean physics in the western equatorial Pacific are of primary importance to the climate system given the role of salinity in the stratification of the ocean and in ENSO variability
It is important that coupled models, including CMIP5 models, have the capability to reproduce the effect of salinity on SST, and determine the potential resulting barrier layer (BL)
Summary
It is well known that ENSO is Earth’s dominant source of interannual climate variability in the tropical Pacific. Coupled ocean–atmosphere models are able to reproduce the salinity effect on SST, as well as the potential resulting feedback To study this feedback mechanism or for forecasting purposes, for example, a hierarchy of models has been designed. Because a process-based model evaluation can help identify the cause of specific biases, the following questions were investigated: Can the interannual salinity variations of the tropical Pacific be realistically described by BNU-ESM? A summary of the study’s key findings is provided in the final section
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