Research brief: The mystery of vertical mixing in the eastern Pacific cold tongue

In this study, the researchers used a high-resolution numerical simulation of the cold tongue region to show that strong turbulent mixing occurs not only on the Equator, but also off the Equator on the edge of the cold tongue associated with passing energetic oceanic waves with periods of 15-40 days known as Tropical Instability Waves.

Picture: Breaking wave. Credit: Emiliano Arano (Pexels).

Oceanic heat uptake in the cold tongue of the eastern Pacific ocean plays a crucial part in setting the global climate system’s average state as well as influencing modes of variability such as the El Nino/Southern Oscillation.

This heat uptake is enhanced by vertical mixing within the cold tongue – and yet little is known about the spatial and temporal structure of this mixing. In this study, the researchers used a high-resolution numerical simulation of the cold tongue region to show that strong turbulent mixing occurs not only on the Equator but also off the Equator on the edge of the cold tongue associated with passing energetic oceanic waves with periods of 15-40 days known as Tropical Instability Waves.

These results strongly motivate the need for observational campaigns that can extend current equatorial measurements of mixing to off-equatorial regions.

Paper: Cherian, D., Whitt, D., Holmes, R. M., Lien, R-C., Bachman, S. and Large, W. (2021): Off-equatorial deep-cycle turbulence forced by Tropical Instability Waves in the equatorial Pacific. Journal of Physical Oceanography, accepted.