The Poloidal Convection Model and Multi-Scale Moist Circulations

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Tall cumulus clouds produce most heavy rains globally. They form as air rises from near the surface to the upper reaches of the atmosphere. To make room for the ascending, moisture-laden air, cool, dry air is forced downward around the cloud. The ascending air forms visible cloud droplets and rain drops within it, but the descending air is largely invisible and may extend to distances far away from the cloudy core. The importance of this pairing of ascent and descent to the behavior of cloud is appreciated, but it is not well described. Current models and descriptions of raining convective clouds focus on the air that ascends inside the cloud and greatly simplify the descending portion. The project aims to remedy this by incorporating both ascending and descending air in one framework. By doing so, it will be possible to understand some observed behavior of convective clouds for the first time. For example, the project aims to mathematically describe how tall convective clouds interact with one another through their three-dimensional flow and thus how individual clouds coalesce to form heavily raining, long-lived weather systems and to better understand why and when certain shaped clouds grow and why others do not. This understanding will then be incorporated into a model to assess and forecast global precipitation patterns and behavior. The project will also train students at various levels in interdisciplinary research. The project will test and further develop a new model that describes an arbitrary convective circulation as poloidal. The poloidal model will be contrasted with a plume model. By coupling convective ascent and descent with a smoothly varying complete velocity field, the project will develop descriptions of dynamical aspects of clouds and circulation such as how advection and diffusion affect growth and decay of circulations, how pairs of circulations interact, and how localized latent heating within updrafts contributes to spinning up or down the return circulation. By simultaneously incorporating dynamical aspects of poloidal circulations into a simple model, it will be possible to address long standing questions like how individual convective circulations feed upscale to synoptic ones like the Madden Julian Oscillation.This award reflects NSF's statutory mission and has been deemed worthy of support through evaluation using the Foundation's intellectual merit and broader impacts review criteria.