"A new flow instability, known as zig-zag instability, has been revealed to be at the origin of the spontaneous formation of decoupled horizontal layers in stably stratified fluids (density decreasing along the vertical). Such layered structure is widely observed in the atmosphere and oceans. It governs the vertical transport of pollutants and chemical components and the dissipation of momentum. A critical problem is, for example, the thermal inversion in urban areas that causes the stagnation of pollutants and small particles in the lower part of the atmosphere. The main goal of this research is to investigate the linear and nonlinear evolution of the zig-zag instability in complex stratified flows as previous work has been restricted to prototype flows. This will improve the fundamental understanding of stratified turbulence, a crucial step towards developing accurate parametrization of stratified turbulence in numerical models of the atmosphere and oceans. The research will be carried out through theoretical and numerical studies and with new designed laboratory experiments and measurement techniques which may result in the development of patents with the collaboration of the European industry. This project provides the opportunity to work on a highly interdisciplinary topic at an internationally renowned institution, the Laboratoire d'Hydrodynamique at Ecole Polytechnique, offering the possibility to translate research results into academic papers and patents, which can be used in both academic and practitioner contexts. Understanding the dynamics of stratified turbulence will be valuable to improve climate models and to support future predictions in forthcoming Intergovernmental Panel of Climate Change reports."