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1. Introduction

Polar stratospheric clouds (PSC) provide particle surface for heterogenous chemistry leading to chlorine activation and thus to ozone destruction in the polar stratosphere in spring. In the Arctic, the temporal and spatial PSC occurrence is highly dependant on the variability of the polar vortex and the resulting temperature distribution. Atmospheric models usually assume large-scale PSC occurrence below T_NAT, but observations lead to a more sophisticated view.

Different PSC types and formation conditions have been identified, and the role of stratospheric lee-wave events leading to PSC formation in Northern Scandinavia has been discussed in detail (Carslaw et al., 1998a+b; Dörnbrack et al., 1999). Still, the Scandinavian mountain ridge is not solely responsible for all mesoscale PSC incidents.

Here, PSC events observed by LIDAR (Light Detection and Ranging) in Sodankylä, Northern Finland (67.37°N, 26.65°E), and Ny-Ålesund, Spitsbergen (78.93°N, 11.95°E) are discussed.

The position of the observation sites relative to the polar vortex is taken into consideration, focussing on filamentary structures at the vortex edge. It is shown that other mesoscale processes apart from lee-waves have an effect on PSC formation at the vortex edge.