ACPD Atmospheric Chemistry and Physics Discussions ACPD 1680-7375 Copernicus GmbH Göttingen, Germany 10.5194/acpd-9-14735-2009 UV Raman lidar measurements of relative humidity for the characterization of cirrus cloud microphysical properties Di Girolamo P. 1 Summa D. 1 Lin R.-F. 2 3 Maestri T. 4 Rizzi R. 4 Masiello G. 1 Dipartimento di Ingnegeria e Fisica dell'Ambiente, Univ. of Basilicata, 85100 Potenza, Italy Goddard Earth Sci. and Technology Center, Univ. of Maryland Baltimore County, MD, USA Mesoscale Atmospheric Processes Branch, NASA GSFC, Code 613.1 Building 33, Greenbelt, MD 20771 USA Dipartimento di Fisica, Università di Bologna, viale Berti-Pichat 6/2, 40127 Bologna, Italy 08 07 2009 9 4 14735 14769 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/9/14735/2009/acpd-9-14735-2009.html The full text article is available as a PDF file from http://www.atmos-chem-phys-discuss.net/9/14735/2009/acpd-9-14735-2009.pdf

Raman lidar measurements performed in Potenza by the Raman lidar system <i>BASIL</i> in the presence of cirrus clouds are discussed. Measurements were performed on 6 September 2004 in the frame of Italian phase of the EAQUATE Experiment. <br><br> The major feature of <i>BASIL</i> is represented by its capability to perform high-resolution and accurate measurements of atmospheric temperature and water vapour, and consequently relative humidity, both in daytime and night-time, based on the application of the rotational and vibrational Raman lidar techniques in the UV. <i>BASIL</i> is also capable to provide measurements of the particle backscatter and extinction coefficient, and consequently lidar ratio (at the time of these measurements only at one wavelength), which are fundamental to infer geometrical and microphysical properties of clouds. <br><br> A case study is discussed in order to assess the capability of Raman lidars to measure humidity in presence of cirrus clouds, both below and inside the cloud. While air inside the cloud layers is observed to be always under-saturated with respect to water, both ice super-saturation and under-saturation conditions are found inside these clouds. Upper tropospheric moistening is observed below the lower cloud layer. <br><br> The synergic use of the data derived from the ground based Raman Lidar and of spectral radiances measured by the NAST-I Airborne Spectrometer allows to determine the temporal evolution of the atmospheric cooling/heating rates due to the presence of the cirrus cloud anvil. <br><br> Lidar measurements beneath the cirrus cloud layer have been interpreted using a 1-D cirrus cloud model with explicit microphysics. The 1-D simulations indicates that sedimentation-moistening has contributed significantly to the moist anomaly, but other mechanisms are also contributing. This result supports the hypothesis that the observed mid-tropospheric humidification is a real feature which is strongly influenced by the sublimation of precipitating ice crystals. Results illustrated in this study demonstrate that Raman lidars, like the one used in this study, can resolve the spatial and temporal scales required for the study of cirrus cloud microphysical processes and appears sensitive enough to reveal and quantify upper tropospheric humidification associated with cirrus cloud sublimation.

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