Multidecadal Intensification of Atlantic Tropical Instability Waves

Tropical Instability Waves (TIWs) are the dominant source of intraseasonal variability in the central equatorial Atlantic and play an important role in the redistribution of heat in the upper ocean. Here we use multidecadal records of sea surface temperature, sea level anomaly, sea surface salinity, and near-surface currents constructed from in situ and satellite observations to reveal a long-term intensification of the intraseasonal variability of these variables due to an increase of TIW activity. Enhanced barotropic energy conversion from increased covariance of horizontal current fluctuations, rather than low-frequency changes of the mean zonal currents, drives the TIW intensification. As a consequence, boreal summer cooling of tropical North Atlantic surface waters through horizontal eddy temperature advection increased by 0.03 degrees C month(-1) decade(-1) during 1993-2021, a change of 74% +/- 53% relative to the long-term mean. The presented multidecadal TIW trends are strongly modulated by interannual variations like the 2021 Atlantic Nino.

Automated summary

Tropical Instability Waves (TIWs) are the dominant source of intraseasonal variability in the central equatorial Atlantic and play a crucial role in redistributing heat in the upper ocean. A study using multidecadal records of various oceanic variables has shown a long-term intensification of intraseasonal variability, particularly due to increased TIW activity. This pattern is driven by enhanced barotropic energy conversion from the covariance of horizontal current fluctuations.