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                        2015. április 21.
                          kedd, 14 óra
             ELTE TTK északi épület, 5.128-as terem

                         Patrice Le Gal
 CNRS Institut de Recherche sur les Phénomenes Hors Equilibre (IRPHE),
        and Aix-Marseille Université, Marseille, France

            "An Experimental and Numerical Study of
      Cyclones and Anticyclones in Rotating Stratified Flows"


Stratified rotating fluid flows are well described by the thermal wind 
equation
from which we obtained a new scaling law describing the shape of 3D vortices.
This new law has been confirmed experimentally and numerically and also
using measurement data of Atlantic Ocean Meddies and Jovian vortices. One
consequence of this law is that inside the cyclones (anticyclones) the fluid
should be more (less) stratified than the ambient fluid. This means that to
generate a cyclone in Nature, a process must produce both a cyclonic eddy and
locally a super-stratification. We conducted laboratory experiments and
numerical simulations to study 3D cyclones and anticyclones. Anticyclones are
produced by a localized injection while cyclones are generated by a local
suction. We show that this latter process produces indeed regions both
super-stratified and with a cyclonic rotation, but with a more complex
structure than expected. Our study provides a new understanding of the
asymmetry between cyclones and anticyclones observed in Nature as it seems
easier to mix a region of fluid than to super-stratify the fluid as it is the
case inside cyclones. An extension of this work to understand the shape of
floating oceanic vortices will finally be discussed.



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