Interdecadal Variability Of Sea Surface Salinity In The Tropical Pacific And Its Modulation On ENSO

Based on observations,reanalysis,and model simulation datasets,the decadal characteristics of salinity in the tropical Pacific and the relationship between temperature and salinity were analyzed.Further research included the relationship between decadal salinity and Interdecadal Pacific Oscillation(IPO)in tropical Pacific,and the modulation and mechanism of the decadal salinity variation on ENSO.In addition,some models of CMIP5 and CMIP6 were evaluated based on the analytical results.It was found that the high salinity variability was concentrated within the mixed layer,and the relative contribution of the decadal variability reached about 60%.Corresponding to temperature,there was a remarkable decadal pattern of salinity in Pacific.Salinity and the related physical fields were not simply reversed symmetrical changes under different IPO phases.The averaged salinity in Equator Key Area(EKA)had an advancing relationship with the TPI leading about 10-20 months.The surface forcing aim at the effect of subsurface on salinity budgets,and then influenced each other.Under the further action of surface advection,the salinity in EKA had changed in advance.The interannual variability was affected and modulated by the decadal variability in the tropical Pacific in spatial mode,range and intensity of ENSO with phase asymmetry.That was to say,the decadal variabilities of salinity had different contributions to the El Nino and La Nina events within the positive and negative phases of the IPO.For the strength of ENSO,in the positive phase of IPO,decadal salinity contributed positively to El Nino and negatively contribution to La Nina;In the negative phase of IPO,it has a negative contribution to El Nino and a positive contribution to La Nina.As far as the duration of the event is concerned,the duration of the El Nino in the positive phase of IPO had been extended to a certain degree,and the La Nina event in the negative phase of IPO did so as well.The models of CMIP5 and CMIP6 were selected to conduct a preliminary assessment on the decadal variability in the tropical Pacific.The simulation of the salinity decadal variability was obviously different among models with excessive high variability and zonal displacement.There were some uncertainty in simulating the relationship between decadal temperature and salinity in models.The CMIP6 models had a significant improvement over the CMIP5 in the simulation of the decadal salinity spatial pattern,which was manifested in the eastward shift of the equatorial high value area,and the improvement in the simulation bias of the CMIP5 model to the negative sea surface salinity anomaly in the South Pacific Convergence Zone.Based on the analysis in this study,the reasons for the decadal variability of ENSO characteristics can be discussed from the aspect of ocean multi-scale motion interaction,and a theoretical basis for ENSO prediction can be provided.In particular,the analysis of the relationship between salinity variability and decadal climate changes in the tropical Pacific can provide us with a new viewpoint and method for monitoring and forecasting climate change.