Discovery of Chile Niño/Niña.

A new air‐sea coupled mode is discovered off the coast of northern Chile and named Chile Niño/Niña. It shows remarkable interannual variability in sea surface temperature (SST) with the peak in austral summer from January to March. The related warm (cold) SST anomalies are mainly generated by anomalous southward (northward) alongshore surface winds that suppress (enhance) the coastal upwelling and subsurface mixing and, in turn, reinforce the wind anomalies by heating (cooling) the overlying atmosphere and strengthening the anomalous cross‐shore pressure contrast. The positive feedback is called the coastal Bjerknes feedback in analogy to the equatorial Bjerknes feedback that is responsible for generation of El Niño–Southern Oscillation. The anomalous surface shortwave radiation through the SST‐low stratus cloud thermodynamic feedback and the variation in the mixed‐layer depth play positive roles in the evolution of Chile Niño (Niña). In contrast, the wind‐evaporation‐SST feedback plays almost no role in the evolution. Plain Language Summary: The coastal air‐sea coupled modes occur along eastern boundaries of most of major subtropical oceans and have noticeable biogeochemical impacts on marine ecosystems. However, no such phenomenon has been reported in the southeast Pacific so far. Here, by carefully removing the influence of El Niño–Southern Oscillation, we have discovered a new coastal climate mode off northern Chile and named it Chile Niño/Niña. The intrinsic climate mode along the coast is generated by the coastal Bjerknes feedback among alongshore surface winds, coastal upwelling, and the SST anomalies. The anomalous surface shortwave radiation and the variation in the mixed‐layer depth contribute to the evolution of Chile Niño/Niña. Our results reveal the existence and generation mechanism of Chile Niño/Niña for the first time, which advance our knowledge of ocean‐atmosphere‐land coupled interactions and may provide new insights into the research of marine ecology and blue economy. Key Points: A new intrinsic climate mode is discovered off the coast of northern Chile and named Chile Niño/Niña for the first timeThe coastal Bjerknes feedback involving the ocean‐atmosphere‐land interaction plays an essential role in generating Chile Niño/NiñaThe anomalous shortwave radiation by a stratus cloud feedback and variation of the mixed‐layer depth influence Chile Niño/Niña evolution [ABSTRACT FROM AUTHOR]