Applied Mathematics Seminar | Amir Atoufi, Topographically driven stratified turbulent mixing

MC 5501

Speaker

Amir Atoufi, University of Cambridge

Title

Topographically driven stratified turbulent mixing

Abstract

Stably stratified shear flows are key to many environmental and geophysical applications. The local dynamics of such flows involve a competing interaction between (stabilising) stable stratification and (destabilising) background shear. These flows can also be significantly affected by topography. In this talk, I will present various topographical effects on stratified shear flow dynamics such as internal hydraulics as well as lateral, and vertical confinement.

In doing so, I will present results from high-resolution simulations, laboratory experiments, and mathematical modelling of stratified shear flows. It will be argued these topographical effects can have considerable non-local influence on the mixing processes and therefore can impose extra challenges for mixing parametrisations in climate models that have been so far overlooked. A two-layer hydraulic theory linked with long-wave instability is employed to justify the non-local effects of internal hydraulics. I will further introduce a viscous three-layer hydraulic model that accounts for viscous effects and the dynamically important middle layer in stratified shear flows. Theoretical predictions are confirmed by a series of direct numerical simulations and experiments. The non-local effects of lateral and vertical confinement are also discussed. I will conclude by relating the findings to topographical mixing processes in the Arctic Ocean, the atmospheric boundary layer, and estuaries. Finally, I mention the challenges ahead and pose fundamental fluid dynamics problems based on the presented topics that are relevant to climate adaptation and mitigation.