Internal gravity waves that are similar to surface waves of the ocean are ubiquitous in stratified fluids. Understanding of their dynamics (their transfer of momentum and their collapse generating turbulence) is necessary to explain the jet stream structure at high altitudes and the meridional overturning circulation in the ocean. I have worked on understanding how the jet stream influences gravity waves whose sources are parameterized stochastically and how the momentum transport by gravity waves in turn influences the jet stream. Another thread of research involves the understanding of the mechanism for spontaneous gravity and acoustic wave generation by a balanced flow and understanding of wave-interaction processes leading to wave breaking.
Shear instability is a fundamental, universal process in geophysical fluids and one of the main sources of turbulence and mixing in the atmosphere and the ocean. In my research I have focused on over-reflection of gravity waves, which is the mechanism at the heart of stratified shear instability, and investigated the role of non-normality of the operator governing the linear dynamics of small perturbations around a shear flow on the over-reflection process. I have also investigated the non-normal growth of perturbations leading to the emergence of coherent structures in the atmospheric boundary layer and the mechanisms underlying the instability o a shear layer with a free surface that lead to surface wave generation and breaking.
Self-organization of geophysical macroturbulence
Large scale turbulence in geophysical flows is observed to self-organize into long-lived coherent structures like zonal jets and large scale vortices. The jets control the transports of heat and chemical species in the atmosphere as well as provide the storm track for weather systems, while the vortices produce significant spatio-temporal variability. My current research involves understanding of turbulence self-organization using a theory for the statistical state dynamics of the turbulent flow. The research efforts focus on the dynamical system that governs the evolution of the flow statistics and the investigation of its fixed points that are the climate states of the turbulent flow and the investigation of their instability that underlies regime transitions in the flow. The advantage is that this system is deterministic and amenable to the powerful tools of traditional stability theory and it also allows for the careful investigation of the wave-mean flow interactions underlying most of the important phenomena in a turbulent flow.