MC 5501

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.