Climatology of Arctic polar stratospheric clouds as measured by lidar in Ny‐Ålesund, Spitsbergen (79°N, 12°E)

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Polar stratospheric clouds (PSCs) are observed by lidar at the Koldewey Station in Ny‐Ålesund, Spitsbergen (79°N, 12°E). Here we present a PSC climatology for the period 1995/1996–2003/2004, when the Arctic stratosphere was not disturbed by the presence of volcanic aerosols. The study is restricted to only five of these winters, i.e., when the stratospheric temperatures over Spitsbergen were cold enough for PSC formation. The typical altitude range where PSCs are found is 20–24 km, with a downward shifting of the cloud altitude level occurring during the season. Liquid PSCs, the majority of the observations, are usually detected from mid‐January onward; nitric acid trihydrate (NAT) is more frequent in early winter. Furthermore, NAT is generally located at lower altitudes than the liquid clouds. In this data set we rarely observe NAT enhanced PSCs, and ice clouds are entirely absent. In addition to the traditional PSC classification scheme (types Ia/Ib and II) the detected clouds are distinguished according to their vertical thickness, and they are grouped in two categories (thick and thin PSCs), as in a previous study performed on the Antarctic McMurdo PSC data set. The analysis reveals that in Ny‐Ålesund the spatial‐temporal distribution of thick and thin PSCs corresponds to NAT and liquid cloud signatures, respectively. Comparison between the Ny‐Ålesund and the McMurdo PSC climatologies is also reported. In both records, thick and thin PSCs show similar altitude distribution, while discrepancies between the Arctic and Antarctic cases exist for the appearance of NAT and liquid PSCs during the polar winter.