Net energy dissipation in the tropical ocean and ENSO dynamics: modeling and theoretical study.

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This project seeks to estimate net energy dissipation in the tropical Pacific ocean in a broad range of frequencies from sub-annual to decadal and to explore how energy dissipation affects certain characteristics of the El Nino / Southern Oscillation (ENSO) phenomenon (its period, amplitude and other properties). The project has four interconnected components: (i) to compute net dissipation rates associated with large-scale motion in the tropical ocean; (ii) to systematically explore the role of various physical mechanisms, and model parameterizations, that control those rates; (iii) to investigate how different values of those rates affect the simulation of ENSO by state-of-the-art coupled ocean-atmosphere general circulation models; and (iv) to use intermediate coupled models and theoretical considerations to elucidate the effect of oceanic energy dissipation on the properties of El Nino. The ultimate task of this project is to develop the energetics into a standard diagnostic tool for general circulation models.Intellectual Merit:Prior studies of ENSO have established that in a continual oscillation, La Nina corresponds to a state of maximum Available Potential Energy (APE), El Nino to a state of minimum energy, since APE is a measure of the thermocline slope in the tropical ocean. The work done on the ocean by the winds modifies the ocean circulation and buoyancy fluxes, thus creating or destroying APE. Energy dissipation in the ocean tends to reduce this work. The equation describing this energy balance encompasses intrinsic nonlinear dynamics of the system and thus provides a convenient mathematical tool for studying nonlinear oscillations. The energetics also offer a standard unifying approach when dealing with different models. The energy balance will be used to investigate how different characteristics of the models affect the energy dissipation rates, and, on the other hand, how changes in energy dissipation affect the properties of ENSO. Preliminary theoretical results support the importance of dissipation in controlling or influencing the main characteristics of ENSO. Ultimately, knowing the net energy dissipation rates associated with large-scale oceanic motion in the tropics will help to resolve an unsettled problem of the tropical climate theory - whether the ENSO cycle is self-sustained or damped. Broader Impacts:The project is aimed at exploring fundamental mechanisms that control the dynamics of ENSO as observed in nature and as simulated by coupled climate models. It will lead to a better simulation of El Nino by general circulation models (GCM). The development of coupled models for the simulation of seasonal and inter-annual climate fluctuations is progressing rapidly but the goal of a reliable El Nino prediction is still out of reach.. A part of this project is to make the development of coupled GCMs more systematic by evaluating large-scale dissipative properties of the oceanic component of coupled models. Transforming the energy-based approach into a diagnostic tool for coupled GCMs will facilitate comparison of different models and contribute to the progress towards a realistic simulation of seasonal-to-inter-annual climate variability. This will be of direct value for climate prediction. Another important part of this project is to develop global climate modeling capacities at Yale University, which will benefit both graduate and undergraduate students by introducing them to modern numerical approaches in climate research. These modeling capacities will be used in the research work of the students supervised by the PI, and in undergraduate senior projects, while research results originated through this proposal will be used in the classes currently taught or being developed by the Principal Investigator. The modeling capabilities will also contribute to collaborative research with other Yale faculty, and will be made available for educational use to the broader Yale community. The proposed educational plan includes the education of a Ph.D. student in climate dynamics.