Mesoscale controls on cumulus convection

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Cumulus convection is a critical atmospheric process, causing severe weather on the local scale and regulating the atmospheric circulation on the global scale. Despite the fundamental importance of this process, the understanding and prediction of it remain incomplete. As a result, short-term forecasts of severe weather and future climate projections remain highly uncertain, failing to provide reliable guidance to vulnerable sectors of society. The long-term objective of my research program is to improve the quantitative understanding of cumulus convection and apply that knowledge toward improved weather and climate prediction.******This proposal builds on recent progress by my research group in the physical understanding of cumulus convection, in particular the quantification of sub-cloud mesoscale circulations and the strong links between these circulations and cloud-layer convection. In particular, stronger circulations give rise to larger and more vigorous clouds that better overcome the suppressive effects of entrainment (the ingestion of environmental air) and ascend deeper.******My proposed research program provides multiple pathways to build on this understanding and translate it into improved prediction, each conducted by a different graduate student under my supervision. First, a promising theoretical model of sub-cloud mesoscale forcing will be applied to the prediction of such forcing in large-scale models, to improve their representation of convection initiation. Second, a new observational retrieval of cumulus entrainment will be developed and tested using Observation System Simulation Experiments (OSSEs). Third, climatologies using this retrieval will be conducted to quantify the impacts of sub-cloud forcing and other environmental parameters on entrainment in different climate regimes. Fourth, intensive observations from the 2015 Toronto Pan Am Games will be exploited to quantify the role of lake breezes and other mesoscale processes in controlling cumulus convection around Toronto. Fifth, cloud-resolving ensembles of Canadian convection events will be conducted to understand the multi-scale processes regulating these events and evaluate a potential method for improving short-range convection forecasts.******Through its innovative ideas for the quantification of elusive processes, and for its translation of new insights into improved weather and climate prediction, my research program benefits both Canadian society and the international research community. In particular, its scientific advancements are geared toward mitigating severe-weather risks faced by end-users across Canada and narrowing the currently large uncertainties on future climate projections. The training of multiple research personnel will also contribute to the next generation of Canadian natural scientists tackling problems of regional and worldwide significance.