Different Influencing Mechanisms of Two ENSO Types on the Interannual Variation in Diurnal SST over the Nino-3 and Nino-4 Regions

In this paper, the different effects of the eastern equatorial Pacific (EP) and central equatorial Pacific (CP) Ocean El Nino-Southern Oscillation (ENSO) events on interannual variation in the diurnal sea surface temperature (SST) are explored in both the Nino-3 and Nino-4 regions. In the Nino-3 region, the diurnal SST anomaly (DSSTA) is negative during both EP and CP El Nino events and becomes positive during both EP and CP La Nina events. However, the DSSTA in the Nino-4 region is positive in El Nino years and negative in La Nina years, which is opposite to that in the Nino-3 region. Further analysis indicates that the incident shortwave radiation (SWR), wind stress (WS), and upward latent heat flux (LHF) are the main factors causing the different interannual variations in the DSST. In the Nino-3 region, decreased SWR and increased LHF lead to a negative DSSTA in EP El Nino years, and enhanced WS and increased LHF cause a negative DSSTA in CP El Nino years. Conversely, in that same region, increased SWR and decreased LHF lead to a positive DSSTA in EP La Nina years, and reduced WS and decreased LHF cause a positive DSSTA in CP La Nina years. In the Nino-4 region, the reduced trade wind plays a key role in producing the positive DSSTA, whereas the decreased SWR has an opposite effect that reduces the range of the DSSTA during both EP and CP El Nino events, and conversely the enhanced trade wind plays a key role in producing the negative DSSTA, whereas the increased SWR has an opposite effect that increases the range of the DSSTA during both EP and CP La Nina events.