The use of an Adaptive Mesh Refinement Transport Code to study the 2002 Antarctic polar vortex evolution

Walter E. Legnani1, Pablo O. Canziani2,3, Alan O'Neill4, and Nikolaos Nikiforakis5

1 Instituto de Cálculo - Universidad de Buenos Aires - Argentina2 Programa de Estudios de Procesos Atmosféricos en el Cambio Global –Pontificia Universidad Católica Argentina/CONICET – Argentina

3 Departamento de Ciencias de la Atmosfera y los Océanos, Universidad de Buenos Aires/CONICET - Argentina4University of Reading - U.K.

5University of Cambridge - U. K.

A new Adaptive Mesh Refinement transport code is used for the first time to model the Southern Hemisphere stratosphere during a highly perturbed period that led to the unprecedent Antarctic sudden warming event during 2002. This warming led to the splitting of the vortex/ozone hole system. Nevertheless this splitting process is only very distinct at the top and bottom of the region considered, i.e. in the middle stratosphere and the lowermost stratosphere. The AMR code is capable of reproducing the fine structure of the system under study, in good agreement with the GOME assimilated total ozone and the broad fine structures detectable in PV calculations from the NCEP reanalysis. The model results were able to detect significant mixing process, through lamination between the vortex and the surrounding atmosphere. Finally the evolution of the vortex in the lowermost stratosphere confirms the influence of synoptic scale perturbations in the dynamics of the region

The study case

The southerm vortex split in 2002

Why Adaptive Meshes ?

Because of the physics and chemistry that must be resolved!If the processes happen on a certain scale and if they are important for your

model and if you cannot account for this physics and chemistry by subgrid-scale modeling …

you must resolve the problem at the scale involved.

The AMR Model Results – The Evolution of 2002 Vortex Splitting at 850K as an Example

850K - 18-09-02 850K - 19-09-02 850K - 20-09-02 850K - 21-09-02 850K - 22-09-02

850K - 23-09-02 850K - 24-09-02 850K - 25-09-02 850K - 26-09-02 850K - 27-09-02

SUMMING UP

AMR schemes are very efficient during the integration of transport equations to study fine scale structures. They require low hardware resources. The adaptation criteria involve the physics of the participating processes. The vortex splitting was a phenomena with a strong 3D characterisation The filaments of the lobes and the inner mixing zones were put in evidence only with the model more than any other kind of observations. Particularly interesting is the difference between the splitting, separation and dilution of one of the lobes at the upper and lower limits of the vertical range, and the apparent re-merger and delayed dilution of the smaller lobe in the centre of the vertical domain with respect to the other two levels. The comparison of the EP-flux evolution for waves 1 and 2 (not shown) with the sequence of model PV fields shows the pre-eminence of wave 2 in the whole process, while wave 1 is primarily responsible for displacing the whole system off the polar region into mid latitudes where the solar radiation further contributed to the warming and weakening of the vortex and its remains.