Geophysical turbulence

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The atmosphere is an extremely turbulent fluid: weather systems, hurricanes, thunderstorms, and dust devils are all manifestations of atmospheric turbulence. The enormous range of length scales involved, from the planetary scale of more than 10,000 km to the viscous dissipation scale of 1 mm, is at the heart of the theoretical and computational challenge presented by weather and climate prediction. Due to limited computational resources, numerical models of the atmosphere cannot resolve this full range of scales, and motions on the order of tens or even hundreds of kilometers are often not captured explicitly. However, turbulence on these scales is extremely important for the atmosphere as a whole: it mixes heat, water vapor, and pollutants, dissipates energy, and can even excite large-scale motion. These missing processes must be accounted for in atmospheric models, and in the absence of a comprehensive theory for turbulence, this is usually done in an ad hoc manner. My research program aims to advance our understanding of atmospheric turbulence in the mesoscale, which corresponds to the range of motions with length scales between around 1 and 1000 km. It is in the mesoscale where weather and climate models are truncated, and an improved understanding of turbulence in this regime is necessary if its effects are to be better represented in atmospheric models. Idealized numerical simulations will be employed to investigate the fundamental dynamical processes of mesoscale turbulence. Specific open questions that will be addressed include the nature of the mesoscale energy cascade from large to small scales; the injection of mesoscale energy by clouds; and the effect of non-uniform density stratification, such as that found near the planetary boundary layer and tropopause. At the same time, new computational tools will be developed and employed to exploit clusters and massively parallel computers, which are becoming increasingly accessible. This work will help to assess the ability of weather and climate models to accurately reproduce mesoscale turbulence and will inform strategies for improvements.