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Title: Aerosol effects on microphysical processes and deep convective clouds
Author: Heikenfeld, Max
ISNI:       0000 0004 8503 0224
Awarding Body: University of Oxford
Current Institution: University of Oxford
Date of Award: 2019
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Aerosol-cloud interactions are an essential feature of the Earth's climate system. How- ever, aerosol effects on deep convection are highly uncertain. Different conceptual models for the effects of aerosols on deep convective clouds have been proposed, and assessments based on both models and observations show a wide range of results. This thesis aims at unravelling the cloud microphysical pathways involved in these interactions using a hier- archy of different model simulations and novel analysis tools. A detailed pathway ana- lysis based on microphysical process rates for individually tracked clouds is developed and applied to idealised supercell simulations with three different microphysics schemes in a cloud-resolving model (CRM). This reveals both consistent responses between the schemes, e.g. a suppression of warm rain formation and elevated freezing, and signific- ant differences between the schemes due to the definition of hydrometeor classes and microphysical processes. The cloud tracking framework tobac is developed to provide a consistent way to perform analyses resolving the time evolution of individual clouds in a wide range of datasets. Its application is demonstrated for both CRM simulation results and geostationary satellite data. The cloud tracking and the pathway analysis are combined to investigate deep convective clouds in a large case study simulation and their aerosol response for two different CRMs. Separating the tracked clouds into different categories and compositing along a relative time axis allows for a detailed assessment of the cloud microphysics that resolves the time evolution of the clouds. Despite some similar aerosol responses like a suppression of warm-rain formation and surface precipit- ation, the analyses highlight significant differences in the cloud types and cloud evolution simulated by the two models, especially regarding the mixed- and ice-phase processes. The detailed investigation of the microphysical evolution of individually tracked clouds reveals important pathways for aerosol effects on deep convective clouds and substantial uncertainties that arise from the representation of microphysical processes in numerical models.
Supervisor: Stier, Philip Sponsor: Natural Environment Research Council ; EU Framwork 7 (BACCHUS project) ; EU Horizon 2020 (RECAP project)
Qualification Name: Thesis (Ph.D.) Qualification Level: Doctoral
EThOS ID:  DOI: Not available
Keywords: Climate ; Deep convective clouds ; Cloud physics ; Aerosol-cloud interactions ; Microphysics ; Atmospheric physics