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3. Discussion

The common explanation for the larger probability of PSC genesis in Sodankylä is the possibility of lee-waves. Those mesoscale waves may be induced by the Scandinavian mountain ridge and propagate upwards into the stratosphere, where adiabatic cooling leads to temperature fluctuations. Thus, the local temperature may fall below T_NAT and induce particle formation.

Another possibility for the enhanced incidence of PSC above Sodankylä could be the different distribution of trace gases at the vortex edge compared to the vortex centre. As T_NAT and T_ICE both highly depend on the H₂O amount in the stratosphere, areas of enhanced H₂O may lead to PSC formation by raising the threshold temperature. A positive anomaly of 1 ppmv in water vapor amounts in a raise of about 1 K in the threshold temperature.

As the vortex edge is an area of high filamentation, laminae in ozone profiles are frequently observed (Reid et al., 1993; Manney et al., 1998) and can be expected in other trace gases. With laminae in water vapor, T_NAT locally can be raised.