Lidar observations of natural and volcanic-ash-induced cirrus clouds

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Cirrus clouds, composed entirely of ice particles, play a crucial role in the Earth’s radiation budget by scattering incoming solar radiation (cooling effect) and absorbing outgoing radiation (warming effect). However, their influence has not been quantified. This thesis aims to enhance our understanding of cirrus clouds through lidar measurements and model simulations. The first part presents observations from a backscatter lidar over Jülich, focusing on establishing a representative cirrus climatology. A temporal average extinction profile is obtained, considering multiple scattering corrections. Climatological observations are analyzed with additional meteorological data, addressing macrophysical, radiative, and microphysical aspects, and compared to other mid-latitude lidar climatologies. Most cirrus clouds were linked to synoptic weather patterns, exhibiting a significant vertical thickness of about 2.2 km, primarily occurring just below the tropopause. Mean and median optical depth values are approximately 0.28 and 0.12, respectively, with a range from 0.002 to 3. The most frequently observed ice water content (IWC) was 6 ppmv, ranging from 0.01 to 400 ppmv. Lidar observations confirm the lowest IWC values detected by aircraft in situ measurements (∼ 0.01 ppmv), providing clarity on the ability of in situ instruments to detect the thinnest cirrus clouds.