CNRS-NSF Workshop on
Three-dimensional Stratified and Sheared Turbulent Flows:
Comparison between DNS, LES and Observations

Paris, December 19-20th, 2001


Francis Dalaudier
Service d'Aeronomie, Verrieres-Le-Buisson, France

High resolution measurements within the stratosphere

This presentation will focus on simultaneous high resolution measurements obtained within the lower stratosphere either in situ, under small balloons or remotely by a VHF atmospheric radar.

In a first part, the measurement principle will be shortly described and the characteristics of the obtained data will be discussed with emphasis on (time and space) resolution and coverage, noise related limitations, accessible spectral characteristics (scales). As an illustration, data samples will be presented and some small scale dynamics characteristics of the stratosphere will be emphasized.

In a second part, selected open scientific questions resulting from the analysis of experimental stratospheric data will be discussed. Two example of dynamical (Richardson) instability resulting from strong wind shear (either modulus shear or direction shear), and related questions about their time evolution in both situations. Experimental hints about the evolution of the edges of a mixing (or mixed) layer and about subsequent instabilities and entrainment phenomena will be presented.

The possibility to investigate (and answer) these questions through numerical simulation will be stressed with special emphasis on the requirements in terms of resolution and coverage.

 

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