ACPD Atmospheric Chemistry and Physics Discussions ACPD 1680-7375 Copernicus GmbH Göttingen, Germany 10.5194/acpd-11-11379-2011 Denitrification and polar stratospheric cloud formation during the Arctic winter 2009/2010 Khosrawi F. 1 Urban J. 2 Pitts M. C. 3 Voelger P. 4 Achtert P. 1 Kaphlanov M. 1 Murtagh D. 2 Fricke K.-H. 5 6 MISU, Stockholm University, Stockholm, Sweden Department of Radio and Space Science, Chalmers University of Technology, Göteborg, Sweden NASA Langley Research Center, Hampton, USA Swedish Institute of Space Physics (IRF), Kiruna, Sweden formerly at: Physikalisches Institut der Universität Bonn, Bonn, Germany deceased, 10 August 2010 12 04 2011 11 4 11379 11415 This is an open-access article ditributed under the terms of the Creative Commons Attribution License, which permits unrestricted use, distribution, and reproduction in any medium, provided the original author and source are credited. This article is available from http://www.atmos-chem-phys-discuss.net/11/11379/2011/acpd-11-11379-2011.html The full text article is available as a PDF file from http://www.atmos-chem-phys-discuss.net/11/11379/2011/acpd-11-11379-2011.pdf

The sedimentation of HNO<sub>3</sub> containing Polar Stratospheric Cloud (PSC) particles leads to a permanent removal of HNO<sub>3</sub> and thus to a denitrification of the stratosphere, an effect which plays an important role in stratospheric ozone depletion. The polar vortex in the Arctic winter 2009/2010 was very cold and stable between end of December and end of January. Strong denitrification was observed in the Arctic in mid of January by the Odin Sub Millimetre Radiometer (Odin/SMR) which was the strongest denitrification that had been observed in the entire Odin/SMR measuring period (2001–2010). Lidar measurements of PSCs were performed in the area of Kiruna, Northern Sweden with the IRF (Institutet för Rymdfysik) lidar and with the Esrange lidar in January 2010. The measurements show that PSCs were present over the area of Kiruna during the entire period of observations. The formation of PSCs during the Arctic winter 2009/2010 is investigated using a microphysical box model. Box model simulations are performed along air parcel trajectories calculated six days backward according to the PSC measurements with the ground-based lidar in the Kiruna area. From the temperature history of the trajectories and the box model simulations we find two PSC regions, one over Kiruna according to the measurements made in Kiruna and one north of Scandinavia which is much colder, reaching also temperatures below <i>T</i><sub>ice</sub>. Using the box model simulations along backward trajectories together with the observations of Odin/SMR, CALIPSO (Cloud-Aerosol Lidar and Infrared Pathfinder Satellite Observations) and the ground-based lidar we investigate how and by which type of PSC particles the denitrification that was observed during the Arctic winter 2009/2010 was caused. From our analysis we find that due to an unusually strong synoptic cooling event in mid January, ice particle formation on NAT may be a possible mechanism that caused denitrification during the Arctic winter 2009/2010.

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