Math Modeling Seminar: Atmospheric transfer of kinetic energy across planetary-scale circulation and weather

Math Modeling Seminar
Atmospheric transfer of kinetic energy across planetary-scale circulation and weather

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Dr. Pejman Hadi Sichani
Postdoctoral Associate, Department of Mechanical Engineering
University of Rochester

Abstract:
Earth's atmosphere is a complex, multi-scale dynamical system that continuously exchanges energy across a broad range of spatial and temporal scales. Analyzing the nonlinear transfer of Kinetic Energy (KE) across scales is central to understanding and predicting atmospheric evolution. This nonlinear coupling is a primary factor limiting weather forecasts over long timescales. Traditionally, such analysis relied on spherical harmonics, which are inherently global and cannot provide local information connecting scales with circulation patterns geographically. To address this, we apply a coarse-graining scale-analysis framework, which enables us to create global geographic maps of the KE cascade at any scale for the first time. This is made possible by generalizing the definition of convolution to ensure that the filtering operator and spatial derivatives on the sphere commute. In addition to an upscale cascade, we find a significant downscale KE cascade at scales smaller than synoptic scales. In the troposphere, we find direct KE exchanges between the planetary-scale circulation and smaller scales, including mesoscale motions. The exchanges occur in latitudinal bands of alternating upscale and downscale KE transfer driven by the Hadley, Ferrel, and polar cells. The physics behind such transfer is not due to a classical turbulence cascade, but is due to the action of planetary-scale strain against anisotropic effective pressure arising from sub-planetary-scale motions. These findings offer a novel perspective for exploring the interplay between weather and climate.

Speaker Bio:
Pejman Hadi Sichani earned his Ph.D. in Mechanical Engineering from the Vienna University of Technology, Austria. His doctoral research used Direct Numerical Simulations (DNS) to study the interaction of thermal and solutal stratification with wall-bounded turbulence, exploring internal gravity waves, energetics, and irreversible mixing in stably stratified flows. In 2022, he joined the University of Rochester, NY, as a Postdoctoral Associate in the Department of Mechanical Engineering, where he investigates atmospheric flow dynamics using scale-by-scale analysis, with a focus on kinetic energy transfer across scales in the troposphere and stratosphere. His research interests include computational fluid dynamics, turbulence theory, environmental and geophysical fluid dynamics, and high-performance computing.

Intended Audience:
Beginners, undergraduates, graduates. Those with interest in the topic.