Interactions Between Nonlinear Internal Ocean Waves and the Atmosphere

Abstract

The heterogeneity in surface roughness caused by transient, nonlinear internal ocean waves is readily observed in coastal waters. However, the quantifiable impact this heterogeneity has on the marine atmospheric surface layer has not been documented. A comprehensive data set collected from a unique ocean platform provided a novel opportunity to investigate the interaction between this internal ocean process and the atmosphere. Relative to the background atmospheric flow, the presence of internal waves drove wind velocity and stress variance. Furthermore, it is shown that the wind gradient adjusts across individual wave fronts, setting up localized shear that enhanced the air-sea momentum flux over the internal wave packet. This process was largely mechanical, though secondary impacts on the bulk humidity variance and gradient were observed. This study provides the first quantitative analysis of this phenomenon and provides insights into submesoscale air-sea interactions over a transient, internal ocean feature.

Plain Language Summary The ocean surface appears rough because the wind applies a tangential force to the water, which deforms the surface, generating short and steep waves. These small waves, in turn, increase the friction felt by the wind as it blows across the ocean surface, thereby setting up a feedback mechanism that physically links, or couples, the lower atmosphere to the upper ocean. However, our understanding of this interaction in the case of a heterogeneously rough ocean surface is limited. Using a unique ocean platform, we have collected a novel and complete data set demonstrating the impact internal ocean waves have on the near-surface atmospheric variability, through their modulation of the ocean surface roughness. The surface currents associated with internal waves generate bands of smooth and rough water that travel coherently with the internal wave packet. Our analysis shows that these transient surface features have a distinct and profound impact on the physical characteristics and structure of the near-surface atmosphere. In particular, internal waves enhance the wind forcing over the ocean and individual wave fronts significantly alter the vertical wind gradient. Our results provide the first documentation of the impact internal waves have on the atmosphere and suggest that these dynamics should be accounted for when studying fine-scale atmosphere-ocean interactions and the impact internal waves have on the marine environment.