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Ocean Surface Topography from Space
SCIENCE
Multi-scale interactions in ocean satellite and in situ observations and model outputs: response of quasi-permanent mesoscale features to low-frequency variations in the large-scale background


Author:

Nikolai Maximenko - (University of Hawaii, Honolulu)

Collaborator(s):
  Prof. Per Knudsen
Dr. Dmitri Nechaev
(University of Hawaii, Honolulu)
(University of Hawaii, Honolulu)


Abstract:
Over the two last decades, satellite altimeters have collected unique data sets that combine nearly global coverage with uniform high resolution. These data sets span a wide spectrum of wavenumbers and frequencies and they document signals from many phenomena that have very different scales and are controlled by very different physics and that together determine rich dynamics of the ocean.

In this project, we will study two types of multi-scale interactions: (i) the interactions between small and large spatial scales by focusing on the interactions between eddies and striations with the background flow and (ii) the interactions between high- and low-frequency signals of distinctive jets that emerge from a turbulent flow when observations are averaged over several years.

In the first task, we will identify regions and periods (from seasons to a decade) during which the large-scale circulation exhibited anomalous speeds and analyze the effects of these anomalies on striation patterns and on mesoscale eddy movements. The study of these effects will, among other things, help to better understand the dynamics of the interaction between eddies and a baroclinic flow.

In the second task, we will study the variability of the Kuroshio Extension, the Gulf Stream, and the Agulhas Return Current, in order to analyze the internal structure of each of the jets and the changes in their structures that are associated with jet meanderings and their interactions with eddies. We will also investigate the nature and frequency of countercurrents and recirculations that are often detected on the flanks of the main jets and the role these negative lobes play in keeping the current narrow on multi-year averages.

To achieve the goals of the project, we will improve the mean dynamic topography (MDT) products by synthesizing altimetry with data from the GOCE gravity mission and in situ drifter, Argo, and wind datasets. New methods will be developed to obtain higher resolutions of the MDT and at higher latitudes and in dynamically more complicated regions than currently available. Moreover, the description of the geostrophic circulation will be expanded to intermediate depths of the ocean.

Outputs of the OFES and HYCOM ocean circulation models will be used to optimize the parameters of these new methods in the data analyses, and to interpret the results. The improved descriptions of the surface circulation will be used, in turn, to improve the models for simulating the motion of marine debris and other pollutions on the ocean surface.



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