Georgy ManucharyanI am a Postdoctoral Scholar at the California Institute of Technology, Division of Geological and Planetary Sciences and starting from June 2019 I will be moving to the University of Washington, School of Oceanography as an Assistant Professor. My research resides at a synergetic overlap between geophysical fluid dynamics, physical oceanography, and climate dynamics, currently focusing on the Arctic Ocean and sea ice dynamics. You can find a brief description of my research here.
Phone: (626) 395-8715
ResearchOur climate is affected by the inherently turbulent oceanic flows in which the energy is being continuously transferred across a wide range of scales. An accurate understanding of small-scale processes and their interactions with large-scale flows remains as one of the big challenges in our ability to model and comprehend climate system as a whole. My interests are in exploring fundamental processes governing the dynamics of the Arctic Ocean. The general approach I take is aimed at gaining fundamental knowledge by reducing complex oceanographic phenomena to their core driving mechanisms. My methods are primarily based on the development and exploration of testable theories guided by insights from numerical modeling and supported by observational data analysis and laboratory experiments.
Below is a brief description of the research I am involved in.
Climate models commonly use a Viscous-Plastic sea ice rheology as a model of internal stresses arising from floe interactions. However, its treatment of ice as a continuous medium only applies at scales sufficiently large for floe interactions to have meaningful statistics, O(100 km) and larger. At smaller scales, which are critically important for ice-ocean interactions, individual floe dynamics dominate, and continuous rheology models are inadequate. I am working on a concept of a new Lagrangian ice floe model that will explicitly simulate interactions between individual floes that have realistic shapes without assuming continuous rheology. The model will consist of mechanical and thermodynamic components, giving the advantage of direct comparisons and validations against on-sight and satellite floe observations.
Video: a prototype of an ice floe model that simulates elastic interactions between floes driven by eddying ocean currents (see if you can catch some bugs in the video). In addition to shape-conserving interactions, the future versions of the model will include floe mergers during thermodynamic growth and ridging, as well as fractures leading to the creation of new smaller floes. Achieving realistic sea ice mechanics will be the cornerstone of the floe model.
Global warming with its strong polar amplification resulted in a substantial reduction of the Arctic sea ice thickness and concentration. As a result, both mechanical and thermodynamic sea ice - ocean interactions have strengthened and lead to enhanced footprints of ocean eddies in sea ice characteristics. The 'turbulent' sea ice, i.e. carrying signatures of ocean eddies and filaments, is evident during summer seasons for concentrations less than about 60%.
Video: sea ice vorticity (normalized by f) as simulated by the 1/48 degree ocean model (MITGCM) at the Jet Propulsion Laboratory, Caltech\NASA. Note the presence of strong submesoscales in marginal ice zones and mesoscale eddies throughout the Arctic when the sea ice melts.
Localized and episodic fluxes due to submesoscale oceanic turbulence, currents with O(1) Rossby numbers, play an important role in the vertical transport of heat and nutrients. In the Arctic Ocean, despite being strongly dissipated by the sea ice cover, the submesoscale eddies have significant kinetic energy and may actively interact with overlying sea ice by either redistributing it through mechanical motion or by enhancing vertical heat fluxes that modify its growth/melt rates. In turn, the multi-fractal nature of sea ice cover (and its corresponding buoyancy fluxes) provides conditions for highly non-homogeneous buoyancy and momentum fluxes that generate submesoscale eddies. These mechanical and thermodynamical interactions are particularly prominent in marginal ice zones -- regions of most considerable uncertainties in sea ice forecasts.
Recently the Arctic Ocean has accumulated a large amount of freshwater largely stored within the Beaufort Gyre. The accumulation was linked to changing atmospheric winds which can cause a release of the accumulated fresh waters with global climate implications possible provided they reach deep convection regions. Nonetheless, the basic gyre dynamics are not well understood and it is unclear how much FWC can be held in under such persistent forcing and how quickly can these fresh waters be released. Combining theory with numerical simulations I work to explore the dominant physical processes governing the FWC dynamics: the Ekman pumping and mesoscale eddies that balance to reach equilibrium. It is the interplay between these processes that defines the gyre stability and affects its wind-driven variability.
Sub-mixed layer eddies commonly observed in the Arctic Ocean can affect the melting of sea ice due to increased heat fluxes associated with their turbulent currents. They are typically found at large distances (up to 500 km) away from surface fronts - their assumed formation sites. I use analytical theories and high-resolution ocean model to explore the dynamics of outcropping density fronts and identify the factors influencing the formation of coherent well-separated eddies. An in-depth understanding of the eddy formation and propagation dynamics in the vicinity of outcropping fronts allows identifying the factors influencing the eddy separation distance from the front. This, in turn, brings us closer to quantification of the cross-frontal tracer transport.
The growth of an oceanic mixed layer forced by a surface stress presents one of the testbeds for our understanding of the stratified shear turbulence. The mixed layer deepening depends on a complex interplay between a shear-driven kinetic energy production, and its redistribution between the gravitational potential energy and dissipation. Under relatively weak forcing, persistent secondary mixed layers can be formed below the surface mixed layer. These smaller layers can be generated spontaneously, merge with each other or decay but most importantly they can affect the deepening of the surface mixed layer. I am interested in exploring their dynamics experimentally as well as theoretically.
Density currents, so ubiquitous to geophysical flows, are fluid masses submerged into relatively stationary ambient fluids of different density, with their motion driven by the buoyancy force. The dynamics of such currents are significantly affected by the turbulent entrainment processes that lead to an exchange of their density and momentum with the environment. I investigate the influence of rotation on the efficiency of the turbulent entrainment. Systematically deriving a mathematical model for these currents and making use of turbulent fluxes parameterization it is possible to obtain analytical predictions for the development of the flow demonstrating that the fluid cannot penetrate below this critical level and should spread out horizontally. In conjunction with laboratory experiments, the theory allows to illustrate and quantify the suppression of entrainment due to rotation providing insights into the nature of turbulence in geophysical flows.
In preparation or under review
Not peer reviewed:
Phone: (626) 395-8715
Office: Room 226, Linde + Robinson
Laboratory, ESE, Caltech.
Mailing Address: MC 131-24,
California Institute of Technology,
1200 East California Boulevard,
Pasadena, CA 91125, USA.