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Title: The formation and development of ice and precipitation in convective clouds
Author: Huang, Yahui
Awarding Body: University of Leeds
Current Institution: University of Leeds
Date of Award: 2013
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A combination of modelling studies and synthesis of aircraft data was used to understand the formation and development of ice and precipitation in convective clouds. Two contrasting cases were studied to determine whether supercooled raindrops play an important role in the formation and development of ice and precipitation. It was found that the fast production of graupel by directly freezing of supercooled raindrops was crucial for the activation of the Hallett-Mossop (HM) process in the 18 May case. Low concentrations of raindrops and thus graupel caused the HM process to be ineffective in the 13 July case. Therefore, supercooled raindrops were critical to the ice development regarding the production of graupel. Furthermore, only a few ice particles were required (order of about 0.01 L-1) in order for the HM process to quickly dominate the ice process. Another important aspect regarding the research subject is the effect of aerosols. High concentrations of relatively small ice particles were observed in the 15 July case. The explanation for such high concentrations of ice is likely associated with the type of ice nuclei ingested into the cloud. Biological nuclei, oxidised organic aerosol particles vented from the Murg valley, and desert dust are all possible candidates. A model sensitivity test with biological nuclei produced similar concentrations of ice particles to the observations. Two stages were found in the development of a multi-cell storm that occurred over the Vosges mountains in the 24 August case. The response of cloud dynamics and precipitation to the changes in droplet concentration was negative in the earlier single-cell stage, while it was positive in the later multi-cellular stage. The simulations indicated that the aerosol-induced invigoration of convection and enhancement of precipitation were the result of the interaction between the effect of aerosols on freezing and the effect of cold pools on the cloud development.
Supervisor: Not available Sponsor: Not available
Qualification Name: Thesis (Ph.D.) Qualification Level: Doctoral
EThOS ID:  DOI: Not available