Tropical Instability Waves in the Atlantic Ocean and their implications for ocean-atmosphere variability in high-resolution ICON simulations

Tropical Instability Waves (TIW) in the Atlantic Ocean are an important source of intraseasonal variability in ocean and atmosphere. Recent studies suggest that energy from TIWs propagates downward as Yanai wave beams, providing energy for Equatorial Deep Jets (EDJ). Such EDJs are thought to affect regional climate variability on a multi-year time scale, in particular rainfall over Africa. Due to their small-scale characteristics, TIWs are poorly captured in observations, and high-resolution models are needed to study their related dynamics. However, to date there are no realistic high-resolution models which are capable of simulating EDJs, and investigations into the relationship between TIWs and EDJ development are limited. Therefore, I analyze the global high-resolution (10 km horizontal resolution, 128 vertical levels) ocean only ICON simulation (ICON-O), which is forced with hourly ERA5 atmospheric data for the period of 2000 – 2018, in regard to the presentation of TIWs and EDJs.

In the upper ocean, TIWs are well captured in ICON-O. Furthermore, the simulated TIWs initiate downward and eastward propagating Yanai wave beams which transfer energy into the deep ocean. Despite this, EDJs are not present in the simulation. This suggests that ICON-O is a useful tool for studying upper ocean dynamics related to TIWs, while deep ocean dynamics are misrepresented. Therefore, I conduct sensitivity experiments to explore why the realistically simulated Yanai wave beams in ICON-O do not destabilize into EDJs. My results will provide important insights into why EDJs are generally absent in models with a realistic setup. Hence, this study could help to include realistic EDJs in future simulations. Ultimately, this will allow for studying the impact of EDJs on regional climate in coupled models.