An interdecadal change in the influence of the Central Pacific ENSO on the subsequent north tropical Atlantic spring SST variability around the mid-1980s

Abstract

North tropical Atlantic (NTA) spring sea surface temperature (SST) tends to be warmer (cooler) than normal in Central Pacific (CP) El Nino decaying years during 1960s to mid-1980s. However, the relationship between the NTA spring SST and CP El Nino-Southern Oscillation (ENSO) is weakened after mid-1980s. This study presents this interdecadal change and investigates possible causes. Before the mid-1980s, above-normal NTA SST peaks in post-El Nino spring. The CP El Nino can affect NTA spring SST by inducing a negative phase of North Atlantic Oscillation (NAO) anomaly over North Atlantic from winter to spring. This negative NAO circulation weakens the Azores High and causes weaker than normal trade wind. As a result, less heat loses from the NTA Ocean and above-normal SST anomalies generated. In contrast, after the middle 1980s, the connection between CP ENSO and NAO-like anomaly has been disrupted. This leads to a weakening of CP ENSO influences on the NTA spring SST. The observed change in the relationship between NTA spring SST and CP ENSO is likely related to the state of the polar vortex. Before the middle 1980s, the polar vortex is weak, this favors the propagation of ENSO-related wave flux. The Rossby wave trains spread to the stratosphere during El Nino conditions and cause weaker than normal polar vortex, resulting in a negative NAO in the low levels. And the subtropical jet is enhanced and elongated which provides a potential waveguide for wave activity propagating to the Atlantic through a tropospheric way. However, the polar vortex is strong after mid-1980s, preventing the propagation of the ENSO-related wave trains through the stratosphere or the troposphere.