Konopka, Paul
[Author];
Spang, R.
[Author];
Günther, G.
[Author];
Müller, R.
[Author];
McKenna, D. S.
[Author];
Offermann, D.
[Author];
Riese, M.
[Author]
How homogeneous and isotropic is stratospheric mixing? Comparison of CRISTA-1 observations with transport studies based on the Chemical Lagrangian Model of the Stratosphere (CLaMS)
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Media type:
E-Article
Title:
How homogeneous and isotropic is stratospheric mixing? Comparison of CRISTA-1 observations with transport studies based on the Chemical Lagrangian Model of the Stratosphere (CLaMS)
Contributor:
Konopka, Paul
[Author];
Spang, R.
[Author];
Günther, G.
[Author];
Müller, R.
[Author];
McKenna, D. S.
[Author];
Offermann, D.
[Author];
Riese, M.
[Author]
imprint:
Wiley, 2005
Published in:Quarterly journal of the Royal Meteorological Society 131, 565 - 579 (2005). doi:10.1256/qj.04.47
Footnote:
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Description:
The Chemical Lagrangian Model of the Stratosphere (CLaMS) is used for the interpretation of N2O observed during the CRISTA-1 experiment in early November 1994. By comparing CRISTA data with CLaMS simulations, the impact of the large-scale horizontal deformations on mixing is studied. Using the probability density function technique (PDF) quantifying the statistics of N2O variability, the critical deformation gamma(c) was inferred that triggers the mixing algorithm in CLaMS. The critical deformation gamma(c) measures the ratio between the major and minor axes of the ellipse resulting from the stretching of a circle surrounding a given Lagrangian air parcel, i.e. only deformations stronger than gamma(c) are relevant for mixing in CLaMS.The PDF derived from CRISTA observations at 700 K and on horizontal scales of the order of 200 km is characterized by a Gaussian core and non-Gaussian tails indicating filamentary structures typical for 2D turbulence. The PDFs obtained from CLaMS simulations strongly depend on gamma(c) but only weakly on the horizontal resolution r(0) that was varied between 45 and 200 km. The choice gamma(c) = 0.8 in the model best reproduces the observed PDE This implies that the large-scale isentropic transport leads to scale collapse and subsequent mixing in those parts of the flow where on a time scale approximate to 12 hours and a spatial scale approximate to 200 km the flow stretches a circle to an ellipse with the ratio between the major and minor axes exceeding 5. Owing to the spatial resolution of the CRISTA instrument that smooths out the non-Gaussian tails, the elongation rate approximate to 5 estimates only the lower bound of the critical deformation.Furthermore, our simulations show that air masses of low N2O amounts observed by CRISTA between 20 degrees and 40 degrees S are fragments of the polar vortex that have been peeled from the vortex edge. The history of these fragments can be divided into two phases: formation and mixing of filaments at the vortex edge where gamma > ...