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Article Dans Une Revue Atmospheric Measurement Techniques Discussions Année : 2024

Lidar-radar synergistic method to retrieve ice, supercooled and mixed-phase clouds properties

Résumé

Mixed-phase clouds are not well represented in climate and weather forecasting models, due to a lack of the key processes controlling their life cycle. Developing methods to study these clouds is therefore essential, despite the complexity of mixedphase cloud processes and the difficulty of observing two cloud phases simultaneously. We propose in this paper a new method to retrieve the microphysical properties of mixed-phase clouds, ice clouds and supercooled water clouds using airborne or satellite radar and lidar measurements. This method extends an existing variational method developed for ice clouds retrieval using lidar, radar and passive radiometers. We assume that the attenuated lidar backscatter β at 532 nm is more sensitive to particle concentration and is consequently mainly sensitive to the presence of supercooled water. In addition, radar reflectivity Z at 95 GHz is sensitive to the size of hydrometeors and hence more sensitive to the presence of ice crystals. Consequently, in the mixed-phase the supercooled liquid droplets are retrieved with the lidar signal and the ice crystals with the radar signal, meaning that the retrieval rely strongly on a priori and errors values. This method retrieves then simultaneously the visible extinction for ice α ice and liquid α liq particles, the ice and liquid water contents IWC and LWC, the effective radius of ice r e,ice and liquid r e,liq particles and the ice and liquid number concentrations N ice and N liq. Moreover, total extinction α tot , total water content TWC and total number concentration N tot can also be estimated. As the retrieval of ice and liquid is different, it is necessary to correctly identify each phase of the cloud. To this end, a cloud phase classification is used as input to the algorithm and has been adapted for mixed-phase retrieval. The data used in this study are from DARDAR-MASK v2.23 products, based on the CALIOP lidar and CPR radar observations, respectively from the CALIPSO and CloudSat satellites belonging to the A-Train constellation launched in 2006. Airborne in situ measurements performed on the 7 th April 2007 during the ASTAR campaign and collected under the track of CloudSat-CALIPSO are compared to the retrievals of the new algorithm to validate its performance. Visible extinctions and water contents properties derived from in situ measurements and the retrievals showed similar trends and are globally in good agreement. The mean percent error between the retrievals and in situ is 39 % for α liq , 398 % for α ice , 49 % for LWC and 75 % for IWC. It is also important to note that the temporal and spatial collocations are not 1

Domaines

Météorologie
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Dates et versions

insu-04372406 , version 1 (04-01-2024)

Identifiants

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Clémantyne Aubry, Julien Delanoë, Silke Groß, Florian Ewald, Frédéric Tridon, et al.. Lidar-radar synergistic method to retrieve ice, supercooled and mixed-phase clouds properties. Atmospheric Measurement Techniques Discussions, inPress, ⟨10.5194/amt-2023-252⟩. ⟨insu-04372406⟩
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