The Potential Role of Seasonal Surface Heating on the Chaotic Origins of the El Niño/Southern Oscillation Spring Predictability Barrier.

The Spring Predictability Barrier (SPB) phenomenon is characterized by the reduced accuracy of El Niño/Southern Oscillation (ENSO) forecasts during the spring, which substantially limits our ability to predict ENSO events. By investigating the nonlinear dynamic characteristics of ENSO systems simulated by a box model, we found that the strong surface heating process in spring may contribute to the SPB by regulating the different coupling processes between the ocean and atmosphere. Specifically, the intensified springtime surface heating increases the Sea Surface Temperature (SST), further amplifying the thermal damping effect of SST anomalies and reducing the dynamic connection between zonal SST gradient and upwelling process, and finally increasing the chaotic degree of ENSO systems simulated by the box model. The enhanced chaotic degree of ENSO systems leads to a more rapid growth of initial errors in the forecast model in spring, potentially leading to the SPB phenomenon. Plain Language Summary: The El Niño‐Southern Oscillation (ENSO) is a climate phenomenon characterized by the periodic fluctuation of Sea Surface Temperature (SST) anomaly in the tropical Pacific, which has a significant impact on global weather and climate patterns. However, predicting ENSO evolution several seasons in advance is challenging due to the Spring Predictability Barrier (SPB) phenomenon, which refers to the reduced accuracy of ENSO forecasts during the spring. Our investigation into the nonlinear dynamic characteristics of ENSO systems revealed that the strong surface heating process in spring could be a contributing factor to the SPB. The strong springtime surface heating increases the SST in the eastern tropical Pacific and further affects the different coupled processes between ocean and atmosphere, finally raising the chaotic degree of ENSO systems. As the chaotic degree of ENSO systems increases, initial errors in the forecast model grow more rapidly, which may lead to the SPB phenomenon. Key Points: The box model was utilized to investigate the physical mechanisms for the Spring Predictability Barrier phenomenonThe El Niño/Southern Oscillation systems undergo a chaotic regime transition when the couple processes between the ocean and atmosphere change in springThe strong surface heating in spring may be responsible for the change of couple processes [ABSTRACT FROM AUTHOR]