ELFT HÍRADÓ

[StatFizSzeminar <statfiz AT glu.elte.hu>]

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             ELTE TTK Fizikai Intézet
         STATISZTIKUS FIZIKAI SZEMINÁRIUM


                  2019. március 6.

                       szerda 

                       11.00

                    Imre M. Jánosi


      ELTE Department of Complex Systems

  "Eddy census over the oceans: overview of 
     methods, and a super-vortex proxy"

Mesoscale eddies are energetic, swirling, time-
dependent circulatory flows on a characteristic
scale of around 100 km, which are observed almost
everywhere in satellite altimetry data of global
sea surface height. The total volume transport by
drifting eddies is comparable in magnitude to that
of the large-scale wind-driven and thermohaline
circulations, therefore mesoscale eddies play a 
crucial role in global material and heat transport
and mixing of oceans. In spite of their importance,
it is far from trivial to identify and characterize
such eddies from remote sensing data. The vast 
majority of the related studies is based on some 
automatic algorithm that identifies and tracks the 
eddies from gridded maps of sea level anomaly. 
I give a short overview of Lagrangian and Eulerian
methods to identify mesoscale eddies. The algorithms
based on searching for finite-time Lagrangian 
coherent structures obey a better theoretical 
foundation, nevertheless a recent test of twelve 
different approaches revealed that the various 
methods often produce very different predictions for
coherent structures with false positives and negatives.
Our own empirical flow field data evaluation in a well
studied ocean region along the U.S. West Coast revealed
a surprisingly strong relationship between the surface
integrals of kinetic energy and enstrophy (squared 
vorticity). This relationship defines a single isolated
Gaussian super-vortex, whose fitted size parameter is
related to the mean eddy size, and the square of the 
fitted height parameter is proportional to the sum of 
the square of all individual eddy amplitudes obtained
by standard vortex census. This finding allows a very
effective coarse-grained eddy statistics with minimal
computational efforts. As an illustrative example, the
westward drift velocity of eddies is determined from a
simple cross correlation analysis of kinetic energy 
integrals.


1117, Budapest, Pázmány P. sétány 1/A, Északi tömb 2.54
        honlap: http://glu.elte.hu/~statfiz

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