Interpretation of airborne CASPOL measurements using methods developed in the CLOUD chamber
It is thought that cirrus clouds have a warming influence on the atmosphere. The presence of small(<50 μm) ice crystals in cirrus can complicate matters leading to a net cooling feedback on climate. Additionally, in mixed phase clouds, detection and quantification of small ice particles continue...
| Main Authors: | , , , , , , |
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| Format: | Still Image |
| Language: | English |
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| Online Access: | https://nrc-publications.canada.ca/eng/view/accepted/?id=d590e48b-8096-4043-a124-882141021461 https://nrc-publications.canada.ca/eng/view/object/?id=d590e48b-8096-4043-a124-882141021461 https://nrc-publications.canada.ca/fra/voir/objet/?id=d590e48b-8096-4043-a124-882141021461 |
| Summary: | It is thought that cirrus clouds have a warming influence on the atmosphere. The presence of small(<50 μm) ice crystals in cirrus can complicate matters leading to a net cooling feedback on climate. Additionally, in mixed phase clouds, detection and quantification of small ice particles continue to pose a challenge for classification and derivation of Ice Water Content (IWC). Remote sensing techniques of cloud water and ice particles continue to require in-situ airborne measurements for validation. It was shown in previous studies that it is possible to classify such particles by their unique polarisation signature. The Cloud Aerosol Spectrometer with Polarisation (CASPOL) allows a semi-quantitative derivation of the spherical and aspherical fractions of particles. In this study we combine single, particle-by-particle, polarisation measurements with path averaged depolarisation measurements from chamber experiments at the European Organisation for Nuclear Research (CERN) to improve determination of particle specific polarisation response. We then use this comparison to implement a laboratory developed discrimination method for CASPOL airborne measurements collected as part of the Aerosol-Cloud-Coupling-and-Climate-Interactions-in-the-Arctic (ACCACIA) and the Cirrus-Coupled-Cloud-Radiation-Experiment (CIRCCREX) field campaigns. Results from homogeneously mixed chamber experiments showed good agreement between single particle polarisation and path averaged "remote" depolarisation measurements. However, contributions from larger particles (>50 μm), can lead to discrepancies. Analysis of the aircraft cloud data showed that CASPOL derived aspherical fraction periods in cirrus clouds agreed with image shape analysis collected using a high resolution CCD imaging spectrometer (3-View Cloud Particle Imager, 3V -CPI). Peer reviewed: No NRC publication: No |
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