The geography of near-shelf mixing on the east coast of South Africa.

Autor: Pringle, J., Stretch, D., Tirok, K.
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Zdroj: Environmental Fluid Mechanics; Oct2023, Vol. 23 Issue 5, p1145-1165, 21p
Abstrakt: Direct observations of turbulent mixing in energetic ocean currents are fundamentally important to improving the understanding of stratified turbulence and the predictive capability of ocean models. In this study, we have selected an energetic region of the Western Indian Ocean to make simultaneous measurements of temperature and velocity to directly infer the geography of turbulent mixing on the east coast of South Africa. Direct measurements of the rate of turbulent kinetic energy dissipation, ϵ , were recorded by an autonomous underwater vehicle glider platform and vertical microstructure profiler (VMP). The glider was deployed in the Agulhas current in 2015 over a 200 km transect and measured approximately 250 vertical profiles of turbulent microstructure. Additional vertical profiles near the shelf were obtained from approximately 85 VMP casts during 2018 in a region where the powerful Agulhas current is formed and interacts with the shelf. VMP and glider data collected at Sodwana Bay and the Agulhas current showed evidence of elevated dissipation rates 10 - 8 < ϵ < 10 - 6 Wkg - 1 . Our results indicate that in general turbulent mixing in the Agulhas is concentrated spatially in pancake-shaped patches. Ordinary Kriging was used to interpolate between consecutive profiles and showed that the horizontal scale of the turbulent patches was typically O(1 km) while the vertical scales of the patches ranged between 0.01 and 10 m. Article Highlights: Direct measurements of turbulent dissipation in the strong persistent Agulhas current are presented for the first time using sensors fitted on a glider and vertical microstructure profiler. Ordinary Kriging revealed the geography of mixing and that turbulent mixing in the Agulhas is concentrated spatially in pancake-shaped patches. VMP data collected at Sodwana showed evidence of elevated dissipation rates 10 - 8 < ϵ < 10 - 6 Wkg - 1 . [ABSTRACT FROM AUTHOR]
Databáze: Complementary Index
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