The influence of Amazonian rainfall on the onset of Atlantic Niño and its potential role in modulating the ENSO influence on Atlantic Niños

Abstract:

Using a suite of satellite and insitu observations, our analysis show that an anomalously stronger rainfall and late ending of the wet season over Amazonian in boreal spring can trigger the onset of the Atlantic Niños in early summer. This is a result of an increase of convective coupled Kelvin waves generated by deep convection over the equatorial Amazonia, which propagate eastward and induce westerly surface wind anomalies across equatorial Atlantic. Such an increase of frequency and intensity of the westerly surface wind anomalies can trigger Kelvin waves in the equatorial Atlantic ocean and change the slope of the sea-level height and thermocline depth, as shown by both satellite altimeter and buoy data. These oceanic responses lead to warmer sea surface temperature anomalies over the equatorial central-eastern Atlantic and Gulf of Guinea, leading to the onset of the Atlantic Niños in early summer. As a result, the onsets the Atlantic Niños follow the late endings of the Amazonian rainy seasons. In contrast, the Atlantic Niñas do not necessarily follow the earlier ending of the Amazonian rainy seasons.

It has been well documented in literature that Amazonian rainfall is influenced by both ENSO and the meridional mode of the tropical Atlantic variability. However, such oceanic influence is modulated by the rainforests through its deep roots and seasonal cycle. We will discuss the role of Amazonian rainforests in modulating the influences of ENSO and Atlantic Meridional mode on the zonal mode of the tropical Atlantic variability, especially Atlantic Niños.