4D-VAR Chemical Data Assimilation
	The animation displays the daily variation of the Nitric Acid Trihydrate (NAT) over the Arctic. The time window spans over 15 days. A comprehensive investigation of polar stratospheric clouds carried out by scientists of the Max-Planck-Institut fur Kernphysik, Division of Atmospheric Physics, Germany, highlights that particle composition analysis of cloud layers over the polar regions. It showed that a large fraction of the layers was composed of nitric acid trihydrate (NAT) particles, containing water and nitric acid at a molar ratio of 3:1. This finding is of particular importance for climate monitoring, since the presence of NAT particles enhances the potential for chlorine activation with subsequent ozone destruction, particularly in early and late winter. Click here for abstract. The model used in this application is based on 475K, which corresponds to an isentropic level in the lower stratosphere, close to 60 hPa pressure or 20 km altitude. Source: Bascoe (Belgian Assimilation System of Chemical Observations from ENVISAT)

Keywords: ESA European Space Agency - Agence spatiale europeenne, observation de la terre, earth observation, satellite remote sensing, teledetection, geophysique, altimetrie, radar, chimique atmospherique, geophysics, altimetry, radar, atmospheric chemistry