Joint Seminar: Subsurface Tropical Instability Waves in the Atlantic Ocean in ICON-O and Observations

Tropical instability waves (TIWs) are important for air-sea interactions and regional climate variability. Recent observations in the Pacific Ocean suggest that apart from TIWs at the surface, there also exist subsurface TIWs (subTIWs), which can alter vertical mixing. Previous studies have focused on the impact of TIW dynamics near the surface, however, to properly assess vertical mixing in the upper ocean, it is necessary to improve our understanding of the vertical structure of TIWs and the influence of subTIWs. In this study, we show the presence of subTIWs in the Atlantic Ocean for the first time using mooring observations at 23◦W/4◦N and 23◦W/0◦N. We expand the analysis using 18 years of simulation of the comprehensive, global, high-resolution ocean model ICON-O to characterize subTIWs with regard to their spatial and temporal variability and investigate their influence on vertical mixing. We find subTIWs between 40 m depth and the thermocline and unlike TIWs, subTIWs are active on both sides of the Equator. Further, we show that subTIWs induce an oscillating multi-layer shear structure, suggesting subTIWs to destabilize the mean flow and thereby induce mixing. This is strongest north of the Equator, where both TIWs and subTIWs act simultaneously, implying TIW/subTIW  interactions. We conclude that subTIWs are a distinct feature of the tropical Atlantic  Ocean with regionally varying implications for vertical mixing and heat flux. Hence, fu ture assessments of upper ocean dynamics should not be limited to the effect of TIWs  alone, but also include subTIWs, particularly in subTIW dominated regions.




15:15–16:15 h


Virtual Seminar


Mia-Sophie Specht


Dirk Olonscheck

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