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- Title
Validating Finescale Parameterizations for the Eastern Arctic Ocean Internal Wave Field.
- Authors
Baumann, Till M.; Fer, Ilker; Schulz, Kirstin; Mohrholz, Volker
- Abstract
In the Arctic Ocean, vertical transport of heat by turbulent mixing is ultimately coupled to the sea‐ice cover, with immediate and far‐reaching impacts on the climate and ecosystem. Unfortunately, direct observations of mixing are difficult, expensive and sparse. Finescale Parameterization (FS) of turbulent energy dissipation rate (ɛ) allows for the quantification of turbulence from breaking internal waves using standard measurements, such as profiles of hydrography and velocity. While FS proved to be reliable in mid‐latitudes, the Arctic Ocean internal wave field is distinct in terms of composition and energy level, rendering the applicability of FS uncertain. To test FS in a wide range of eastern Arctic conditions, we compiled data from eight cruises. All profiles used to calculate FS were collocated with in‐situ measurements of ɛ obtained from microstructure profilers. FS was applied between 50 and 450 m below the surface. Results show a satisfactory performance of FS, with 84% of FS‐derived ɛ being within a factor of 5 to observations. This improved to 90% when using lower‐noise velocity profiles of lowered current meters instead of ship‐mounted current meters. In our data, FS performance is independent of the shear‐strain ratio (Rω) and internal wave field bandwidth (N/f), but there is evidence that highly stratified environments with large potential energy, low turbulence and substantially non‐white shear spectra are less suitable for FS. A widely used formulation of FS using only hydrography and a prescribed Rω = 7 results in 73% of FS estimates being within a factor of 5 to observations. Plain Language Summary: Turbulent mixing of water masses can redistribute heat in the ocean. This is especially important in the Arctic Ocean, where turbulent transport of heat from the relatively warm interior could reach the cold surface waters and thus melt sea ice. Unfortunately, direct observations of turbulence are complicated and expensive and therefore sparse. However, turbulence at centimeter scales induced by breaking internal waves can be estimated from standard observations of ocean current and density profiles measured at O(10) $\mathcal{O}(10)$ m scales, using finescale parameterization (FS). FS was designed for the mid‐latitudes in environments and internal wave fields distinct from the Arctic and it is unclear if the method works well in the Arctic. We use data from eight Arctic cruises that performed standard observations together with direct measurements of turbulence. This enables us to test FS and compare the results to direct measurements. We find that 84% of FS‐derived values for the dissipation rate ɛ are within a factor of 5 to observations. This is a fairly good agreement for turbulence measurements and indicates that FS is applicable in Arctic environments. However, we also identified some specific conditions that may be less suitable for FS. Key Points: Comparisons to in‐situ measurements show that Finescale Parameterization (FS) is applicable over a wide range of eastern Arctic conditionsEnergy content and shape of the spectra describing the internal wave field may indicate whether conditions are suitable for FSFor the strain‐only formulation of FS, a shear‐strain ratio of 7 appears to be representative of eastern Arctic conditions
- Subjects
OCEAN waves; TURBULENT mixing; INTERNAL waves; WATER waves; SHEAR strain; WATER masses; SEA ice; SOLAR cycle
- Publication
Journal of Geophysical Research. Oceans, 2023, Vol 128, Issue 11, p1
- ISSN
2169-9275
- Publication type
Article
- DOI
10.1029/2022JC018668