Size distribution time series of a polar stratospheric cloud observed above Arctic Lidar Observatory for Middle Atmosphere Research (ALOMAR) (69°N) and analyzed from multiwavelength lidar measurements during winter 2005

A case study of a polar stratospheric cloud (PSC) is described using multiwavelength (355, 532, and 1064 nm) lidar measurements performed at the Arctic Lidar Observatory for Middle Atmosphere Research (ALOMAR) on 6 December 2005. Rotational Raman signals at 529 and 530 nm are used to derive a temperature field within the cloud using the rotational Raman technique (RRT). The PSC size distributions are retrieved between 1500 and 2000 UTC through a combination of statistical filtering and best match approaches. Several PSC types were detected between 22 and 26 km during the measurement session. Liquid ternary aerosols are identified before about 1600 and after 1900 UTC typically; their averaged retrieved size distribution parameters and associated errors at the backscatter peak are: N o ≈ 1–10 cm −3 (50%), r m ≈ 0.15 μ m (20%), and σ ≈ 1.2 (15%). A mode of much larger particles is detected between 1600 and 1900 UTC (N o ≈ 0.04 cm −3 (30%), r m ≈ 1.50 μ m (15%), and σ ≈ 1.37 (10%). The different PSC types are also identified using standard semiempirical classifications, based on lidar backscatter, temperature, and depolarization. Overall, the characteristics of the retrieved size distributions are consistent with these classifications. They all suggest that these very large particles are certainly nitric acid trihydrate that could have been generated by the strong gravity wave activity visible in the temperature profiles. The results demonstrate that multiwavelength lidar data coupled to both RRT temperatures and our size distribution retrieval can provide useful additional information for identification of PSC types and for direct comparisons with microphysical model simulations.