The initial errors occurring over Pacific-Atlantic Oceans and exerting large disturbing effect on ENSO predictability

Using a novel data analysis method for predictability dynamics, the impacts of initial sea surface temperature (SST) errors over Pacific and Atlantic Oceans on the predictability of eastern and central Pacific El Niño (i.e., EP and CP El Niño) are investigated. The results reveal the initial SST errors that cause large disturbing effects on EP and CP El Niño forecasting, respectively. These initial errors are both exhibiting a positive-negative-positive-negative-positive chain structure along the direction from northwest to southeast over the Pacific for EP and CP El Niño, which resemble a combined mode of North Pacific Victoria Mode (VM), eastern tropical Pacific positive SST pattern (ETPPSP), and South Pacific meridional mode (SPMM); simultaneously, they exhibit a positive-negative meridional dipole pattern over South Atlantic, referred to as South Atlantic subtropical dipole mode (SASD); additionally, there exist initial warm SST anomalies in the equatorial Atlantic for EP El Niño and in the north tropical Atlantic for the CP El Niño. The above initial errors lead to the underestimation of both CP and EP El Niño. Further analyses illustrate that the initial warm SST errors in the north tropical Atlantic are positively correlated with the VM-like error pattern, which competed with the effect of the ETPPSP, makes the intensity of CP El Niño underestimated; whereas the SASD-like error pattern is revealed to have a positive relationship with the SPMM-like error mode, which only exists during EP El Niño period and interacts with the ETPPSP for much weak EP El Niño intensity. It is obvious that, for predicting which type of El Niño will occur, attention should also be paid to the initial sea temperature accuracy in the Atlantic Ocean under the interference effect of the Pacific Ocean temperature uncertainties.