Low-mode internal tides and small scale surface dynamics in the SWOT cal/val region

Anna Savage1, Amy Frances Waterhouse1, Jennifer A MacKinnon1, Jonathan D Nash2, Samuel Maurice Kelly3, Zhongxiang Zhao4, Justin Shapiro5, Andrew J. Lucas6, Louis St Laurent5, Matthias J Lankhorst7 and Uwe Send8, (1)Scripps Institution of Oceanography, La Jolla, CA, United States, (2)Oregon State University, Corvallis, OR, United States, (3)Massachusetts Institute of Technology, Sommerville, MA, United States, (4)University of Washington, (5)Applied Physics Laboratory University of Washington, Seattle, WA, United States, (6)University of California San Diego, Scripps Institution of Oceanography, La Jolla, CA, United States, (7)UCSD, La Jolla, CA, United States, (8)University of California, San Diego, CA, United States
While the mode-1 internal tide is considerably more energetic than higher-mode internal tides, in some locations the mode-1 and mode-2 internal tides have been shown to have comparable sea surface height amplitudes. The shorter wavelengths associated with the higher mode internal tides suggest that they may be more likely to contaminate the low-frequency small scale dynamics targeted by the upcoming SWOT mission. Here, we will examine the implications of low-mode internal tides on the resolution of submesoscale dynamics from satellite altimetry. Our study uses observations from the SWOT cal/val region off of Monterey, CA where we will use observations including 3 month-long moored velocity and density records (Sep-Dec 2019), recently collected in-situ measurements of isopycnal displacement, dissipation, and dynamic height from Dec 2019, and a Coupled-mode Shallow Water model. Due to their differences in phase speed, we expect the mode-1 and -2 tides to lose energy in different time scales and transfer energy over different spatial scales. The slower phase speeds of higher mode internal tides make them more susceptible to interactions with low-frequency eddies, and therefore more likely to dephase on shorter spatial scales, making them nonstationary and invisible to altimetry away from generation. We will provide initial estimates of the differences in vertical modal structure and phase of the mode-1 and mode-2 internal tides as they propagate away from generation, determine the dependence of dissipation on distance from generation, and provide preliminary estimates of the dominant horizontal scales of surface dynamics in the SWOT cal/val region. This work provides a framework for translating a loss of the internal tide surface signal to ocean interior dynamics, and in turn for mapping the submesoscale field.