Understanding Causes and Effects of Changes in the Atmospheric Circulation

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As human activities warm the planet, there is an urgent need to understand the consequences for specific regions. Circulation of air in the atmosphere exerts a strong influence over regional climate: ascending air typically generates precipitation, whereas descending air is typically very dry. As the planet warms, the strength and spatial structure of the atmosphere's circulation is changing, with important consequences for regional patterns of precipitation and dryness. Many questions remain about the physical mechanisms responsible for these circulation changes and the extent to which these changes will influence regional climate. Thus, I am proposing a research program to develop the fundamental understanding of these mechanisms. Such understanding will produce valuable improvements in climate models and greater confidence in climate model projections. For this funding period, the key objectives of my proposed program are: Objective 1: Examine the circulation mechanisms driving long-term changes in extreme precipitation using a state-of-the-art high-resolution model confined to a 128 km by 128 km region. Such a configuration gives us more control over physical inputs to the regional model, thus generating new discoveries regarding what characteristics of those inputs are most consequential for regional changes of extreme precipitation. Objective 2: Compare the spatial structure of swirling motions ("eddies") during extreme precipitation events in observational estimates and simulations of regional climate models. Such work will provide a critical test of models' ability to capture key characteristics of the atmospheric circulation relevant for extreme precipitation in the real world. Objective 3: Test the sensitivity of circulation and precipitation changes to climate model parameters that approximate small-scale vertical motions called "convective updrafts." The current generation of global climate models struggle to accurately simulate the effects of convective updrafts, and our work will discover possible consequences for the simulation of extreme precipitation changes. Objective 4: Examine mechanisms that produce two-way interaction, or "coupling," between clouds and the atmospheric circulation. Different climate models produce different cloud-circulation coupling strength, and this in turn strongly influences how the atmospheric circulation shifts in space over the long-term, with important consequences for regional precipitation. These objectives serve as important steps towards making transformative improvements in model projections of regional climate change. My past work in this area has already stimulated engagement with federal and municipal government in Canada, and the impact of the proposed work will be felt by a range of stakeholders inside and outside Canada (e.g. policymakers, structural engineers, the agriculture industry, insurance companies) with strong interest in anticipating and adapting to regional climate change.