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Eddy memory as an explanation of intraseasonal periodic behaviour in baroclinic eddies
Author(s) -
Moon Woosok,
Manucharyan Georgy E.,
Dijkstra Henk A.
Publication year - 2021
Publication title -
quarterly journal of the royal meteorological society
Language(s) - English
Resource type - Journals
SCImago Journal Rank - 1.744
H-Index - 143
eISSN - 1477-870X
pISSN - 0035-9009
DOI - 10.1002/qj.4030
Subject(s) - baroclinity , eddy , physics , oscillation (cell signaling) , mechanics , transient (computer programming) , flow (mathematics) , zonal flow (plasma) , scale (ratio) , large eddy simulation , statistical physics , classical mechanics , turbulence , computer science , genetics , plasma , quantum mechanics , tokamak , biology , operating system
The baroclinic annular mode (BAM) is a leading‐order mode of the eddy kinetic energy in the Southern Hemisphere exhibiting oscillatory behaviour at intraseasonal time‐scales. The oscillation mechanism has been linked to transient eddy–mean flow interactions which remain poorly understood. Here we demonstrate that the finite memory effect in eddy‐heat flux dependence on the large‐scale flow can explain the origin of the BAM's oscillatory behaviour. We represent the eddy memory effect by a delayed integral kernel that leads to a generalized Langevin equation for the planetary‐scale heat equation. Using a mathematical framework for the interactions between planetary‐ and synoptic‐scale motions, we derive a reduced dynamical model of the BAM – a stochastically forced oscillator with a period proportional to the geometric mean between the eddy memory time‐scale and the diffusive eddy equilibration time‐scale. Our model provides a formal justification for the previously proposed phenomenological model of the BAM and could be used to explicitly diagnose the memory kernel and improve our understanding of transient eddy–mean flow interactions in the atmosphere.