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Woosok Moon: A balanced state consistent with planetary-scale motion for quasi-geostrophic dynamics

Time: Wed 2019-11-06 11.45 - 12.30

Location: Kräftriket, House 6, Room 306

Participating: Woosok Moon

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The role of planetary-scale zonally-asymmetric thermal forcing on large-scale atmospheric dynamics is crucial for understanding low-frequency phenomena in the atmosphere. Despite its paramount importance, good theoretical foundation for the understanding is still lacking. Here we address this issue by providing a general framework for including planetary-scale thermal forcing in large-scale atmospheric dynamics studies. This is accomplished by identifying two distinct geostrophic motions of horizontal length scale \(L\) in terms of the external Rossby deformation length scale \(L_D\): i) \( L\sim L_D\) and ii) \(L\sim\epsilon^{0.5}L_D\), where \(\epsilon\) is the Rossby number. In addition, via multi-scale analysis, we show that the large-scale atmospheric dynamics can be described by mutual interaction between the two scales. The analysis results in planetary geostrophic equations with large-scale thermal forcing that provide the basic balanced states for processes such as the growth of synoptic waves. In the long-time limit, the continuous growth and decay of synoptic waves provides the convergence of horizontal heat and vorticity fluxes, which contributes to the energy flux balance in the planetary geostrophic scale with planetary-scale advection and thermal forcing.