Continuous secondary-ice production initiated by updrafts through the melting layer in mountainous regions
<p>An accurate prediction of the ice crystal number concentration in clouds is important to determine the radiation budget, the lifetime, and the precipitation formation of clouds. Secondary-ice production is thought to be responsible for the observed discrepancies between the ice crystal numb...
| Main Authors: | , , , , , , , |
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| Format: | Article |
| Language: | English |
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Copernicus Publications
2021-03-01
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| Series: | Atmospheric Chemistry and Physics |
| Online Access: | https://acp.copernicus.org/articles/21/3855/2021/acp-21-3855-2021.pdf |
| _version_ | 1819159619970269184 |
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| author | A. Lauber J. Henneberger C. Mignani F. Ramelli J. T. Pasquier J. Wieder M. Hervo U. Lohmann |
| author_facet | A. Lauber J. Henneberger C. Mignani F. Ramelli J. T. Pasquier J. Wieder M. Hervo U. Lohmann |
| author_sort | A. Lauber |
| collection | DOAJ |
| description | <p>An accurate prediction of the ice crystal number concentration in clouds is important to determine the radiation budget, the lifetime, and the precipitation formation of clouds. Secondary-ice production is thought to be responsible for the observed discrepancies between the ice crystal number concentration and the ice-nucleating particle concentration in clouds. The Hallett–Mossop process is active between <span class="inline-formula">−3</span> and <span class="inline-formula">−8</span> <span class="inline-formula"><sup>∘</sup></span>C and has been implemented into several models, while all other secondary-ice processes are poorly constrained and lack a well-founded quantification. During 2 h of measurements taken on a mountain slope just above the melting layer at temperatures warmer than <span class="inline-formula">−3</span> <span class="inline-formula"><sup>∘</sup></span>C, a continuously high concentration of small plates identified as secondary ice was observed. The presence of drizzle drops suggests droplet fragmentation upon freezing as the responsible secondary-ice mechanism. The constant supply of drizzle drops can be explained by a recirculation theory, suggesting that melted snowflakes, which sedimented through the melting layer, were reintroduced into the cloud as drizzle drops by orographically forced updrafts. Here we introduce a parametrization of droplet fragmentation at slightly sub-zero temperatures, where primary-ice nucleation is basically absent, and the first ice is initiated by the collision of drizzle drops with aged ice crystals sedimenting from higher altitudes. Based on previous measurements, we estimate that a droplet of 200 <span class="inline-formula">µ</span>m in diameter produces 18 secondary-ice crystals when it fragments upon freezing. The application of the parametrization to our measurements suggests that the actual number of splinters produced by a fragmenting droplet may be up to an order of magnitude higher.</p> |
| first_indexed | 2024-12-22T16:43:26Z |
| format | Article |
| id | doaj.art-d6c646fec8894e69a6f14e95f99e3444 |
| institution | Directory Open Access Journal |
| issn | 1680-7316 1680-7324 |
| language | English |
| last_indexed | 2024-12-22T16:43:26Z |
| publishDate | 2021-03-01 |
| publisher | Copernicus Publications |
| record_format | Article |
| series | Atmospheric Chemistry and Physics |
| spelling | doaj.art-d6c646fec8894e69a6f14e95f99e34442022-12-21T18:19:47ZengCopernicus PublicationsAtmospheric Chemistry and Physics1680-73161680-73242021-03-01213855387010.5194/acp-21-3855-2021Continuous secondary-ice production initiated by updrafts through the melting layer in mountainous regionsA. Lauber0J. Henneberger1C. Mignani2F. Ramelli3J. T. Pasquier4J. Wieder5M. Hervo6U. Lohmann7ETH Zurich, Institute for Atmospheric and Climate Science, Zurich, SwitzerlandETH Zurich, Institute for Atmospheric and Climate Science, Zurich, SwitzerlandDepartment of Environmental Sciences, University of Basel, Basel, SwitzerlandETH Zurich, Institute for Atmospheric and Climate Science, Zurich, SwitzerlandETH Zurich, Institute for Atmospheric and Climate Science, Zurich, SwitzerlandETH Zurich, Institute for Atmospheric and Climate Science, Zurich, SwitzerlandFederal Office of Meteorology and Climatology MeteoSwiss, Payerne, SwitzerlandETH Zurich, Institute for Atmospheric and Climate Science, Zurich, Switzerland<p>An accurate prediction of the ice crystal number concentration in clouds is important to determine the radiation budget, the lifetime, and the precipitation formation of clouds. Secondary-ice production is thought to be responsible for the observed discrepancies between the ice crystal number concentration and the ice-nucleating particle concentration in clouds. The Hallett–Mossop process is active between <span class="inline-formula">−3</span> and <span class="inline-formula">−8</span> <span class="inline-formula"><sup>∘</sup></span>C and has been implemented into several models, while all other secondary-ice processes are poorly constrained and lack a well-founded quantification. During 2 h of measurements taken on a mountain slope just above the melting layer at temperatures warmer than <span class="inline-formula">−3</span> <span class="inline-formula"><sup>∘</sup></span>C, a continuously high concentration of small plates identified as secondary ice was observed. The presence of drizzle drops suggests droplet fragmentation upon freezing as the responsible secondary-ice mechanism. The constant supply of drizzle drops can be explained by a recirculation theory, suggesting that melted snowflakes, which sedimented through the melting layer, were reintroduced into the cloud as drizzle drops by orographically forced updrafts. Here we introduce a parametrization of droplet fragmentation at slightly sub-zero temperatures, where primary-ice nucleation is basically absent, and the first ice is initiated by the collision of drizzle drops with aged ice crystals sedimenting from higher altitudes. Based on previous measurements, we estimate that a droplet of 200 <span class="inline-formula">µ</span>m in diameter produces 18 secondary-ice crystals when it fragments upon freezing. The application of the parametrization to our measurements suggests that the actual number of splinters produced by a fragmenting droplet may be up to an order of magnitude higher.</p>https://acp.copernicus.org/articles/21/3855/2021/acp-21-3855-2021.pdf |
| spellingShingle | A. Lauber J. Henneberger C. Mignani F. Ramelli J. T. Pasquier J. Wieder M. Hervo U. Lohmann Continuous secondary-ice production initiated by updrafts through the melting layer in mountainous regions Atmospheric Chemistry and Physics |
| title | Continuous secondary-ice production initiated by updrafts through the melting layer in mountainous regions |
| title_full | Continuous secondary-ice production initiated by updrafts through the melting layer in mountainous regions |
| title_fullStr | Continuous secondary-ice production initiated by updrafts through the melting layer in mountainous regions |
| title_full_unstemmed | Continuous secondary-ice production initiated by updrafts through the melting layer in mountainous regions |
| title_short | Continuous secondary-ice production initiated by updrafts through the melting layer in mountainous regions |
| title_sort | continuous secondary ice production initiated by updrafts through the melting layer in mountainous regions |
| url | https://acp.copernicus.org/articles/21/3855/2021/acp-21-3855-2021.pdf |
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