ACP Atmospheric Chemistry and Physics ACP 1680-7324 Copernicus GmbH Göttingen, Germany 10.5194/acp-5-1301-2005 Analysis of water vapor LIDAR measurements during the MAP campaign: evidence of sub-structures of stratospheric intrusions D'Aulerio P. 1 2 Fierli F. 1 Congeduti F. 1 Redaelli G. 2 Institute for Atmospheric Sciences and Climate, CNR, Roma, Italy Department of Physics, University of L’Aquila, L’Aquila, Italy 01 06 2005 5 5 1301 1310 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.net/5/1301/2005/acp-5-1301-2005.html The full text article is available as a PDF file from http://www.atmos-chem-phys.net/5/1301/2005/acp-5-1301-2005.pdf

This paper presents two case studies of transport of dry air in the free troposphere measured by a ground based Raman LIDAR in the Northern-Italy, during the Mesoscale Alpine Programme (MAP). Two observations characterized by the presence of anomalously dry layers, below 6 km height, were analyzed using Lagrangian techniques. These events are related to upper-tropospheric, high Potential Vorticity (PV) streamers crossing the Alpine region. These are interpreted as small-scale features of stratospheric intrusions associated with the PV ridge during its phase of dissipation. One of the measurements also shows the presence of two distinct dehydrated structures associated with the same event. The water vapor concentration also suggests dilution processes of dry stratospheric air in the troposphere. Lagrangian simulations allowed to successfully reproduce the observed water vapor distribution and the air parcel histories confirmed the stratospheric origin of the dry layers.