The Influence of Convectively Coupled Kelvin Waves on Atlantic Niños

Abstract

AbstractAtlantic Niños dominate the equatorial Atlantic variability during boreal summer (June–August). The coupled ocean‐atmosphere processes associated with Atlantic Niños have been extensively documented. However, the role of atmospheric convectively coupled Kelvin waves (CCKWs), which are uncorrelated to those previously identified processes, in triggering Atlantic Niños has been unclear. Here we identify CCKWs using Wheeler‐Kiladis filtering based on 10°S–10°N averaged daily outgoing longwave radiation. CCKWs propagate eastward from South America and induce surface zonal wind anomalies over the equatorial Atlantic Ocean. Strong anomalous CCKWs during spring (March–May) and their associated surface westerly wind anomalies can trigger downwelling oceanic Kelvin waves that change the east–west slope of the thermocline, consequently leading to Atlantic Niño. A causal effect network reveals that interannual sea surface temperature (SST) anomalies in the Atlantic Niño Index area and CCKWs, both in spring, are uncorrelated, but both appear to influence SST anomalies over the Atlantic Niño Index area in summer. The CCKWs are also uncorrelated to other coupled ocean‐atmosphere sources, such as El Niño–Southern Oscillation and Atlantic Meridional Mode. Among a total of 15 Atlantic Niño/Niña events identified for the period of 1980–2017, two‐thirds of the events are linked to CCKWs. In particular, three Atlantic Niña events (1982, 1994, and 2005) are mainly triggered by CCKWs, under unfavorable SST preconditions. Thus, CCKWs in spring, due to atmospheric internal variability, provide another mechanism for triggering Atlantic Niños and probably weaken their predictability.