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4. Conclusion

In Ny-Ålesund, in the centre of the polar vortex, the synoptic scale conditions with temperatures below T_NAT were not always sufficient for particle formation. Under the same synoptic scale conditions in Sodankylä, at the edge of the polar vortex, mesoscale structures induced PSC formation.

In our case study, lee-wave activity can be excluded according to Dörnbrack et al., 2000. Therefore, we could show that other mesoscale processes apart from lee-waves influence PSC formation at the vortex edge.

Dynamical processes at the vortex edge enhance the probability of PSC formation. At the vortex edge, mesoscale air filaments with different properties exist side by side. Intrusions from mid-latitudes contain more condensation nuclei, while filaments from upper polar vortex air contain more water vapor. At the same temperature, filaments with enhanced H₂O content provide a higher threshold temperature T_NAT for PSC formation.

Thus, mesoscale PSC formation may not be restricted to mountain ridges, but may occur everywhere at the edge of the polar vortex.