CALIPSO Observations of Microphysical Changes in Volcanogenic Ice Clouds in the Stratosphere
Abstract
Volcanic eruptions contain a substantial fraction of water along with ash, SO2, and other gas species. Ash is an efficient ice-nucleating particle that can seed volcanic plumes with a significant ice component and ice clouds have been observed in association with volcanic eruptions. The presence of ice with ash makes it difficult to detect the signature of ash using the standard remote sensing techniques in the infra-red. It is of considerable interest therefore to characterize the particles in volcanogenic ice clouds and to explore any possible difference in their microphysics from meteorologically formed ice clouds. We explore the optical properties of the ice clouds detected in the stratosphere associated with several large volcanic eruptions with significant ash content, using backscatter measurements from the space-borne lidar on board CALIPSO. In particular the version 4 level 2 CALIPSO product now discriminates between clouds and aerosols in the stratosphere and further classifies volcanic ash as one of several different stratospheric aerosol subtypes. A marked decrease in the measured total attenuated color ratios in the volcanogenic ice clouds from the Calbuco and Puyehue-Cordon Caulle suggests that the ice particles in these clouds are likely to be considerably smaller than would be found in typical meteorologically-formed ice clouds. This apparent reduction in size is accompanied by a concomitant change in the shape of the particles, as indicated by the decrease in the retrieved particulate depolarization ratios, which imply an overall increase in the sphericity of the particles. In contrast, no clear changes in these parameters were seen in the stratospheric ice clouds associated with the volcanic plumes from the Nabro volcano, which were dominated by sulfate aerosols. We shall also discuss any possible issues relating to the cloud-aerosol discrimination in this context.
- Publication:
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AGU Fall Meeting Abstracts
- Pub Date:
- December 2019
- Bibcode:
- 2019AGUFM.A21K2815K
- Keywords:
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- 3311 Clouds and aerosols;
- ATMOSPHERIC PROCESSES;
- 3314 Convective processes;
- ATMOSPHERIC PROCESSES;
- 4313 Extreme events;
- NATURAL HAZARDS;
- 8409 Atmospheric effects;
- VOLCANOLOGY