Turbulence Transition

Turbulence in natural environments, like the ocean and atmosphere, is typically episodic: it starts from a laminar or less turbulent state and transitions to energetic turbulence, as is shown in the figure through breakdown of a Kelvin-Helmholtz billow. We study the imprint of the transition process on the characteristics of the ensuing turbulence, such as mixing and energy cascade. An analogue Magneto Hydrodynamics problem exits with astrophysical applications, to which we are interested in extending our oceanic work [see MCP13,17].


Mixing

In the ocean, turbulence mixes temperature, salinity, sediments, nutrients, carbon, pollutants etc. Our work has primarily focused on role of such mixing in resurfacing of deep and abyssal waters that form and sink in polar oceans [MP13, Mashayek et al. 17]. Such resurfacing is essential for the ocean overturning circulation.

Turbulent mixing of dense (red) water with the overlying lighter (blue) water. Mixing is relevant to many geophysical applications on a wide range of scales.

Turbulent mixing of dense (red) water with the overlying lighter (blue) water. Mixing is relevant to many geophysical applications on a wide range of scales.


Ocean Turbulence

Internal waves are generated at the surface, bottom and interior of the ocean continuously and propagate in all directions. They nonlinearly interact and breakdown to turbulence and influence the density and momentum budgets on regional and global scale. Connecting our understanding of physics of individual waves or a group of them to actual oceanic environments is challenging and requires a tight coupling of data, theory and models. First panel in the figure below shows generation of internal waves in the deep Southern Ocean just south of Chile. These waves were generated through impinging of ocean eddies and jets over rough topography [a part of DIMES, a UK-US funded field program; see Mashayek et al. 2017]. The second panel shows mixing of Antarctic Bottom Waters (blue) into North Pacific deep waters (red) through mixing in the Samoan Passage [see Alford et al. 2015 & Mashayek et al. 2019].