On the observation of unusual high concentration of small chain-like aggregate ice crystals and large ice water contents near the top of a deep convective cloud during the CIRCLE-2 experiment

J.-F. Gayet, G. Mioche, L. Bugliaro, A. Protat, A. Minikin, M. Wirth, A. Dörnbrack, V. Shcherbakov, B. Mayer, A. Garnier, C. Gourbeyre
2011 Atmospheric Chemistry and Physics Discussions  
During the CIRCLE-2 experiment carried out over Western Europe in May 2007, combined in situ and remote sensing observations allowed to describe microphysical and optical properties near-top of an overshooting convective cloud (11 080 m/−58 • C). The airborne measurements were performed with the DLR Falcon aircraft specially equipped with a unique set of instruments for the extensive in situ cloud measurements of microphysical and optical properties (Polar Nephelometer, FSSP-300, Cloud Particle
more » ... 300, Cloud Particle Imager and PMS 2-D-C) and nadir looking remote sensing observations (DLR WALES Lidar). Quasi-simultaneous space observations from MSG/SEVIRI, CALIPSO/CALIOP-WFC-IIR and CloudSat/CPR combined with airborne RASTA radar reflectivity from the French Falcon aircraft flying above the DLR Falcon depict very well convective cells which overshoot by up to 600 m the tropopause level. Unusual high values of the concentration of small ice particles, extinction, ice water content (up to 70 cm −3 , 30 km −1 and 0.5 g m −3 , respectively) are experienced. The mean effective diameter and the maximum particle size are 43 µm and about 300 µm, respectively. This very dense cloud causes a strong attenuation of the WALES and CALIOP lidar returns. The SE-VIRI retrieved parameters confirm the occurrence of small ice crystals at the top of the convective cell. Smooth and featureless phase functions with asymmetry factors of 0.776 indicate fairly uniform optical properties. Due to small ice crystals the power-law relationship between ice water content (IWC) and radar reflectivity appears to be very different from those usually found in cirrus and anvil clouds. For a given equivalent reflectivity factor, IWCs are significantly larger for the overshooting cell than for the cirrus. Assuming Published by Copernicus Publications on behalf of the European Geosciences Union. 728 J.-F. Gayet et al.: On the observation of unusual high concentration Atmos. Chem. Phys., 12, 727-744, 2012 www.atmos-chem-phys.net/12/727/2012/ www.atmos-chem-phys.net/12/727/2012/ Atmos. Chem. Phys., 12, 727-744, 2012
doi:10.5194/acpd-11-23911-2011 fatcat:dhu2n5355vcghftxr3qoxh2lm4