Balanced and Unbalanced Mesoscale Dynamics

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9417304 Xu Large scale atmospheric systems such as low and high pressure centers are typically governed by a balance of pressure gradient and coriolis forces and are, therefore, termed balanced flow. For small-scale phenomena such as thunderstorms, this balance typically does not hold and these weather features are referred to as being governed by unbalanced flows. The Principal Investigator will perform a numerical and theoretical study of these two flow types. Density current features, squall lines and mesoscale vortices are important mesoscale weather producing systems and often persist over timescales longer than individual convective storms. These long-lived mesoscale structures may involve different types of interactions between the balanced large scale flows and more transient small scale motions. Studying the related balanced dynamics versus unbalanced dynamics may lead to a new understanding of why the concerned structure is long-lived. The balanced (or unbalanced transient) flow component in a mesoscale convective system is likely to be controlled deterministically (or stochastically) by the large scale environmental flow. Identifying the balanced and unbalanced flow components in mesoscale convective systems may provide useful information for improving or developing cloud parameterization schemes for numerical weather or climate prediction models. ***