Climatology of Arctic polar stratospheric clouds as measured by lidar in Ny-Alesund, Spitsbergen [79° N,12° E]

Polar stratospheric cloud (PSC) measurements have been taken by means of a lidar system at the German Koldewey Station in Ny-Ålesund, Spitsbergen [79°N, 12 °E], since 1988. Here we present the first PSC climatology for the high Arctic built on Ny-Ålesund lidar data collected from winter 1995/1996 to 2003/2004, thus avoiding the effects of earlierbackground aerosol enhancement by large volcanic eruptions. As in a similar study performed on the Antarctic McMurdo PSC dataset, a numerical code has been applied to distinguish PSCs based on their vertical structure displayed on the lidar profile. Two cloud categories showing low or high variability of backscattering ratio with altitude are individuated andaddressed as Large and Small Scale Variation PSCs (LSV and SSV, respectively). It is possible to make reliable assumptions concerning the relationship between the obtained PSCcategories and the conditions under which they are likely to form. Ny-Ålesund is typically situated in the centre of the northern polar vortex, where the majority of PSC observations can be linked to the synoptic temperature field. The present study not only provides a general description of PSCs occurring at Ny-Ålesund, but it also focuses on the temporal and spatialvariability of cloud types observed under both LSV and SSV categories. Finally, the comparison with the McMurdo climatology provides an overview of long term inter-hemispheric differences in PSC appearance as measured by ground based lidars.