Polar stratospheric clouds over the Alps

Polar stratospheric clouds (PSCs) typically form in polar regions at temperatures below −78 ∘ C, at altitudes of approximately 20–25 km. Such temperatures are normally not reached over the Alps, as the stratosphere at mid-latitudes generally remains warmer (−60 ∘ C to −70 ∘ C). The documented case, which, to our knowledge, is likely the first observation of PSCs over the Alps at a geographic latitude of 46–47° N, is examined. PSCs at such southern latitudes have neither been previously observed in Central Europe nor detected through satellite data analyses. This case is particularly notable not only for its geographic rarity but also because the nacreous clouds were detected in long-exposure webcam images under moonlight—a phenomenon that has not previously been documented in Central Europe.