National Oceanic and
Atmospheric Administration
United States Department of Commerce


FY 2022

Serendipitous internal wave signals in Deep Argo data

Johnson, G.C., C.D. Whalen, S.G. Purkey, and N. Zilberman

Geophys. Res. Lett., 49(7), e2022GL097900, doi: 10.1029/2022GL097900, View online (2022)

Serendipitous measurements of deep internal wave signatures are evident in oscillatory variations around the background descent rates reported by one model of Deep Argo float. For the 10,045 profiles analyzed here, the average root-mean-square of vertical velocity variances, √(w´2), from 1,000 m to the seafloor, is 0.0045 m s−1, with a 5%–95% range of 0.0028–0.0067 m s−1. Dominant vertical wavelengths, λz, estimated from the integrals of lagged autocorrelation sequences have an average value of 757 m, with a 5%–95% range of 493–1,108 m. Both √(w´2) and λz exhibit regional variations among and within some deep ocean basins, with generally larger √(w´2) and shorter λz in regions of rougher bathymetry or stronger deep currents. These correlations are both expected, since larger √(w´2) and shorter λz should be found near internal wave generation regions.

Plain Language Summary. Ocean density increases with increasing depth, supporting internal waves below the ocean surface. These internal waves are generated near the surface by varying wind forcing such as passing storms and near the bottom by interactions of currents (including tidal) with rough bathymetry (such as seamounts and ridges). They can travel for long distances in both the vertical and the horizontal. When they break, they play important roles in mixing temperature, salinity, and other water properties. Deep Argo is an observing system designed to measure temperature and salinity profiles from the surface to the bottom of the ocean. One model of Deep Argo float serendipitously observes internal wave signals as variations in descent rate data, which it collects primarily for navigation purposes, from the surface to the seafloor. These observations reveal patterns in the magnitudes of these internal wave signals, with stronger internal wave activity near continental rises and mid-ocean ridges and lower levels over smoother abyssal plains. Also, regions with strong deep flows, such as the Samoan Passage through which bottom water is funneled into the North Pacific, or the region south of the Campbell Plateau through which the Antarctic Circumpolar Current flows, exhibit stronger deep internal wave signatures.

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