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
Résumé
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: No 1–10 cm3 (50%), rm 0.15 mm
(20%), and s 1.2 (15%). A mode of much larger particles is detected between 1600 and
1900 UTC (No 0.04 cm3 (30%), rm 1.50 mm (15%), and s 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.
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