An ongoing cooling in the eastern Pacific linked to eastward migrations of the Southeast Pacific Subtropical Anticyclone

Abstract

Previous studies demonstrate that recent global warming hiatuses are associated with an ongoing cooling in the eastern Pacific. However, the possible driver for this cooling remains vigorously debated. Present theories can be generally categorized into three different frameworks, the most prevailing theory considering the increased heat uptake in ocean interior as a direct trigger in cooling the eastern equatorial Pacific, the next regarding the prolonged solar minimum as a potential driver in producing weak radiative forcing over the Pacific, while another suggesting that changes in atmospheric water vapour and aerosols play an unnegligible role in absorbing and reflecting solar radiation. Most recently, some studies argue that the ongoing cooling in the eastern Pacific is induced by a strengthening of the easterly trade winds. Nevertheless, observational records coming from the monitoring buoys deployed along the equator by NOAA since 1992 indicate that an intensification of the trade winds is only confined to the central tropical Pacific (around 170° E–170° W) during hiatus decades, elsewhere along the equatorial Pacific the trade winds exhibit a stable condition even a slight weakening in the eastern equatorial Pacific, rendering it as a trigger of this cooling in the eastern Pacific unlikely. Here we use a model and long-term observational data to demonstrate that a persistent cooling in the eastern Pacific is directly linked to an eastward displacement of the Southeast Pacific Subtropical Anticyclone (SPSA). Interactions between the Andes and an eastward shift of the SPSA generate greater pressure gradients in the eastern flank, in turn, stronger alongshore winds and more intense upwelling, ultimately contributing to hiatus decades.