Assessment Of Tropical Pacific Salinity And Its Modulation On Mean SST And ENSO In CMIP5

Based on the 25 models of Coupled Model Intercomparison Project 5 (CMIP5)piControl simulation, the present study assessed the spatial distribution of the mean sea surface salinity (SSS). The study also evaluated the spatial distribution of SSS for the Eastern Pacific (EP) and the Central Pacific (CP) El Ni(?)o in the tropical Pacific Ocean and explored the relationships among SSS, the sea surface temperature (SST),precipitation and zonal current. The results illustrate that:(1) The spatial skill scores of mean S ST simulated showed the best performance,followed by those of precipitation, zonal current and SSS. The high correlations between SST and SSS explained that SSS had an obvious feedback on SST. The spatial correlation coefficients in the SSS-precipitation, SSS-zonal current explained that both precipitation and zonal current related to the SSS. The correlations between the precipitation and SSS in warm pool as well as in SPCZ were higher than the correlations between the zonal current and SSS. While the correlations between the zonal current in ITCZ and the SSS in the dateline Pacific were greater than the correlations between precipitation and SSS.(2) SSS anomalies were inextricably linked to ENSO events. The first time coefficients of EOF for SSS anomalies were related to EP ENSO index at 10months lead, which caused by westerly wind burst. The second time coefficients of EOF for SSS anomalies were related to CP ENSO index at 5 months lead. The SSS anomalies in the SPCZ were also related to EP and CP ENSO index at 10 months lead.(3) The simulated horizontal distributions of SST and precipitation anomalies for the EP El Ni(?)o were better than those for the CP El Ni(?)o, but the results were opposite for SSS simulation. During the CP El Ni(?)o period, the positions of maximal SST, precipitation and SSS anomalies were clearly shifted to the west and slightly weaker compared with that during the EP El Ni(?)o. The correlations among SST,precipitation and SSS in the CP El Ni(?)o were higher than that in the EP El Ni(?)o,which showed that SST directly affected precipitation, which then subsequently affected SSS significantly. In addition, SSS had an obvious feedback on SST.Compared with that in EP El Ni(?)o, the interaction between SST and SSS might be weaker because of the horizontal advection, the nonlocal effects and other related ocean physics.(4) Based on each SSS skill score simulated,CMIP5 models were divided into two groups. It was found that the maximal position of the variability with the low(high) scores models were located westward (eastward) in the equatorial Pacific,probably due to the position of the equatorial Pacific cold tongue. When the Pacific cold tongue extended westward, the warm SST anomalies moved westward remarkably during the El Ni(?)o events. This resulted in westward shift of precipitation and SSS anomalies at the same time. Meanwhile, the negative SSS anomalies extended southeastward in the low skill score models,which were probably attributed to the effects of the southeastern branch of the double ITCZ that caused more precipitation and freshen SSS. The SSS variability showed a close relationship with SST associated with the evolution of ENSO.