Modulation of Equatorial Currents and Tropical Instability Waves during the 2021 Atlantic Nio

Presenter(s): Dr. Franz Philip Tuchen (AOML/PhOD)

Sponsor(s): NOAA/Atlantic Oceanographic & Meteorological Laboratories (AOML)

Seminar Contact(s): Kandaga Pujiana ; kandaga.pujiana@noaa.govthis link opens in a new window

Location: Hybrid; AOML first floor conference room and onlinethis link opens in a new window

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United States: +1 502-482-3123 Access Code: 204 859 863#

Abstract: Every few years the eastern equatorial Atlantic Ocean is significantly warmer than usual during boreal summer. Such warm events are referred to as Atlantic Nio events, and share similarities with El Nio events in the Pacific. In 2021, the strongest Atlantic Nio in at least four decades was observed in the equatorial Atlantic. This presentation is the first that investigates the complex interaction between Atlantic Nio, tropical Atlantic upper-ocean currents, and equatorial waves based on various observational data sets. It shows that the developing 2021 Atlantic Nio weakened both the background flow and the variability of near-surface currents in May, which in turn largely reduced the strength of intraseasonal (20 to 50 days) waves that are usually generated by instability of the upper-ocean zonal currents. As a consequence, the cooling effect that these waves usually have north of the equator and the warming effect along the equator vanished from May to July 2021. Interestingly, variability of chlorophyll concentration was enhanced, suggesting that enhanced meridional chlorophyll gradients compensated for reduced wave activity.