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[Fizinfo] Stat Fiz Szeminarium

Chronological Thread 
  • From: StatFizSzeminar <statfiz AT>
  • To: fizinfo AT
  • Subject: [Fizinfo] Stat Fiz Szeminarium
  • Date: Thu, 28 Feb 2019 10:44:18 +0100

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ELTE TTK Fizikai Intézet

2019. március 6.



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

1117, Budapest, Pázmány P. sétány 1/A, Északi tömb 2.54

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