The Discovery of New Coastal Climate Mode: Chile Niño/Niña

A new ocean-atmosphere coupled mode is identified in the coastal region of the Southeast Pacific. This coastal mode displays remarkable interannual sea surface temperature (SST) variability off Chile, and we call this Chile Niño/Niña in analogy of equatorial warm/cold ENSO events. It shows a prominent seasonal phase locking feature, with the largest variability appearing in austral summer from January to March (JFM). The warm (cold) SST anomalies associated with Chile Niño (Niña) are observed to grow and decay with anomalous southward (northward) alongshore surface winds, coastal ocean downwelling (upwelling). The associated deceased (increased) cross-shore pressure gradient indicates the existence of an essential role of the coastal Bjerknes feedback in generating Chile Niño (Niña). Moreover, during the developing phase of Chile Niño (Niña), the warm (cold) SST anomalies lead to increased (decreased) downward shortwave radiation through SST–low stratus cloud thermodynamic feedback. Meanwhile, accompanying the reduced (increased) surface wind speed off Chile, the mixed-layer depth there is anomalously shallowed (deepened). Therefore, the combined effects of increased (decreased) shortwave radiation anomaly and thinner (thicker) mixed layer depth also contribute to the developing of Chile Niño (Niña). The present study reports the existence of an intrinsic coastal atmosphere-ocean coupled mode off Chile for the first time, adding a new member to the “coastal Niño/Niña” family.