Decadal Modulation of ENSO Spring Persistence Barrier by Thermal Damping Processes in the Observation.

The spring persistence barrier remains a critical challenge for the prediction of El Niño–Southern Oscillation (ENSO) because it severely limits the potential ability of ENSO forecast across the boreal spring. Our observational analysis shows that the spring persistence barrier exhibited a significant decadal modulation in the last half century. Further analysis shows that this decadal modulation is caused by the decadal variation in spring ENSO stability, which, in turn, is dominated by the thermal damping feedback of the sea surface temperature (SST) through latent heat flux and shortwave radiation flux. The change of the thermal damping feedback is associated with the background mean SST, with a cooler SST corresponding to a greater ENSO instability and a severer spring persistence barrier and vice versa. Plain Language Summary: Obtaining effective and correct El Niño–Southern Oscillation (ENSO) forecasts is always an inspiring and challenging task but requires additional research for optimization. One fundamental obstacle that must be faced is the so‐called boreal spring persistence barrier, which relates to the significant decrease in ENSO's prediction skill that always occurs during the boreal spring. Through investigating the spring persistence barrier issues by the observational analyses, our study proposes a mechanism for controlling its variability on the decadal time scale and highlights the significant effects of the interdecadal climate variability in the tropical Pacific. As the mean state of the tropical Pacific warms, more moisture is released into the atmosphere for the same magnitude of sea surface temperature warming, which further leads to the thermal damping over the tropical Pacific and induces more stable ENSO during the boreal spring. The more stable ENSO then weakens the spring persistence barrier, making ENSO easier to predict. This study will draw the scientific community's attention on understanding about ENSO and ENSO predictability; the decadal variations in spring persistence barrier intensity and its related physical processes should be adequately represented in climate models used for seasonal predictions and studies of climate variability, change, and projection. Key Points: The ENSO spring persistence barrier exhibited a significant decadal variability in the last half centuryThe decadal modulation of the barrier is caused by the decadal variation in spring ENSO stabilityThe ENSO's stability is further dominated by the nonlinear heat flux‐SST damping feedback [ABSTRACT FROM AUTHOR]