Research On The Possible Effects Of Solar Radiation On The Interdecadal Changes Of Tropical Pacific Ocean Temperature And ENSO

In this study,the possible effects of TSI on the main air-sea systems in the tropical Pacific are investigated by using sea surface temperature?SST?data,the20^th-century reanalysis data of the National Oceanic and Atmospheric Administrator?NOAA?and solar radiation is characterized by monthly total solar irradiance?TSI?,it is one of the solar forcing sets of the Sixth Coupled Model Comparison Program?CMIP6?.Firstly,the relationship between TSI and the leading modes of tropical Pacific SST is analyzed,and the influence of TSI on tropical Pacific SST are also studied.Then the possible effects of the TSI on the decadal variation of SST in the tropical central Pacific are diagnosed.Finally,the relationships between TSI and El Ni?o-Southern Oscillation?ENSO?are discussed.The conclusions are summarized as follows:There is a significant correlation between the winter TSI and winter SST in the tropical Pacific from 1910 to 2010.The spatial distribution of the correlation coefficients between the winter TSI and SST in the tropical Pacific displays"-+-"pattern In the meridional direction.That is,notable negative correlation exists the tropical northwest Pacific and the south Pacific along the eastern coast of Australia,while significant positive correlation southwestward extend from the northeast Pacific to the tropical central Pacific,as well as the eastern Pacific along the coast of Peru.Empirical orthogonal function?EOF?decomposition of the winter SST for tropical Pacific shows that the second mode of the winter SST for tropical Pacific is similar to the spatial distribution of correlation coefficients between the winter TSI and SST over tropical Pacific,and the correlation coefficients between the winter TSI and the time series coefficient corresponding to the second mode of winter SST for tropical Pacific are 0.201,significant at 95%confidence level.These imply that there is an intrinsic relationship between the winter TSI and SST for tropical Pacific.By analyzing the regression coefficients of the winter TSI and SST in tropical Pacific as well as the composite for peak and valley values of TSI?divided by?0.8standard deviations?,it can be seen that the spatial distribution of the SST in tropical Pacific region also shows a meridional“-+-”anomalous pattern,which is similar to the spatial distribution of correlation coefficients between winter TSI and SST in tropical Pacific.These results suggest that the formation of the meridional“-+-”SST pattern in the tropical Pacific in winter may be closely related to TSI.Both the SST in the tropical central Pacific and the TSI with a period of quasi-11 year.By comparing the relationships between the TSI index and SST as well as other atmospheric variables,the SST anomaly pattern is featured by the most significantly positive correlation at lag 1-3 years,confirming the presence of the TSI signals in the decadal SST anomalies in the tropical central Pacific but with a lag response.The net shortwave radiation caused in phase by the TSI is clearly the direct contributor to the warming of the tropical Pacific SST on the decadal timescale even though it might be reduced by the cloud-radiation feedback after 2-3 lag years.The positive SST anomalies could induce the surface zonal wind variation and might be in turn enhanced by the westerly wind anomalies through air-sea interaction over the tropical central Pacific.Also,these SST anomalies can warm tropospheric temperature and increase moisture into air,which favor formation of more cloud accompanied with the ascending motion.Both the responses of surface zonal wind and total cloud amount may provide a feedback onto SST itself in terms of dynamical and thermodynamical processes.Based on the mean value of the original sequence of TSI index,the peak and valley periods of TSI are defined,the peak or valley period of TSI corresponds to the eastern ENSO events.This may be due to the heterogeneity of cloud distribution,which results in different solar radiation received on the sea surface.In the peak period of TSI,there is less cloudiness in the tropical eastern Pacific and more cloudiness in the western Pacific.Therefore,more solar radiation can be absorbed on the surface of the tropical eastern Pacific,resulting in the rise of SST in the tropical eastern Pacific,forming an eastern El Ni?o event.In the valley period of TSI,the situation is opposite,forming an eastern La Ni?a event.Then carry out the analysis of SST and 850hPa zonal wind during the peak or valley period of TSI,the results show that the TSI peak and valley periods provide a decadal background for ENSO cycle,and the peak period of TSI mostly corresponds to the occurrence of El Ni?o events,while the valley period of TSI mostly corresponds to the occurrence of La Ni?a events.The 850 hPa zonal wind result is that the westerly anomaly prevails almost in the tropical Pacific during the peak period of TSI.Such wind configuration contributes to the warming of SST in the tropical eastern Pacific and the formation of El Ni?o events.During the valley period of TSI,the easterly anomaly dominants in the middle and eastern Pacific.This can lead to the westward expansion of surface warm sea water and makes the east Pacific cold water surge,conducive to the formation of La Ni?a events.