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Ocean Surface Topography from Space
Dynamics of multiple, migrating quasi-zonal jets in the ocean


Oleg Melnichenko - (University of Hawaii, Honolulu)

  Prof. Ali Bel Madani
(University of Hawaii, Honolulu)

Surface kinetic energy in the ocean is dominated by mesoscale variability or eddies. Eddies are thought to be mainly a product of baroclinic instability, gaining their energy from a huge reservoir of available potential energy associated with the mean circulation. However, the classical view of the ocean circulation as one consisting of the large-scale gyres filled with random eddies appears to be far from accurate. There is a growing body of evidence suggesting that the mesoscale eddy field is not completely random, but is organized into coherent structures that are intermediate in both spatial and temporal scales between the eddies and mean flow. These structures include, but are not limited to, patterns of preferred eddy pathways, as well as transient, migrating quasi-zonal jets, which, while featuring systematic meridional drift, remain coherent over time periods much exceeding a typical eddy life-time. Satellite observations also indicate that transient quasi-zonal jets are able to organize the eddy field into some sort of storm tracks, elongated along the jets and moving with them. Transient quasi-zonal jets and their associated storm tracks represent a marked mode of oceanic low-frequency variability and may play an important role in the ocean component of the Earth’s climate system. Yet, these features remain poorly characterized and understood and are, thus, the focus of the proposed research.

The objectives of the proposed research are to:

  1. provide a systematic description and characterization of transient quasi-zonal jets and storm tracks in the ocean;
  2. generally, quantify their dynamics;
  3. specifically, investigate the dynamical link between the jets, large-scale circulation, and eddy genesis and variability; and
  4. estimate the impact on mixing and transport of tracers.

To achieve these objectives, we will analyze the ~20-year-long satellite altimetry dataset combined with results from ocean general circulation models. Due to the multi-scale nature of oceanic motions, our primary tool to identify and characterize transient quasi-zonal jets in both the altimetry and model data will be a wavenumber frequency spectral analysis of oceanic variability. High-resolution numerical models will also supply information about subsurface variability, essential to provide dynamical interpretation of satellite observations. Comparisons between the models, run with and without inter-annual forcing, will help to quantify the relative importance of the jets and eddies in driving oceanic low-frequency variability. Finally, dedicated numerical experiments with Lagrangian particles will help to evaluate the impact on mixing and transport of tracers.

The proposed research directly addresses the objectives of the Ocean Surface Topography Science Team: (1) to support studies in Physical Oceanography utilizing the combined ~20-year TP/Jason data, preferably jointly with other satellite and in situ data and/or models; and (2) to support studies of high-resolution merged altimetric data sets. The proposed study will help develop a more complete description and dynamical understanding of mesoscale variability in the ocean and its role in shaping the general circulation.

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