New nonlinear mechanisms of midlatitude atmospheric low-frequency variability

PHYSICA D-NONLINEAR PHENOMENA

卷:239

Article

Sterk, A. E.¹  Vitolo, R.²  Broer, H. W.¹  Simo, C.³  Dijkstra, H. A.⁴ 

[1] Univ Groningen, Johann Bernoulli Inst Math & Comp Sci, NL-9700 AK Groningen, Netherlands

[2] Univ Exeter, Sch Engn Comp & Math, Exeter EX4 4QF, Devon, England

[3] Univ Barcelona, Dept Matemat Aplicada & Anal, E-08007 Barcelona, Spain

[4] Univ Utrecht, Inst Marine & Atmospher Res Utrecht, NL-3584 CC Utrecht, Netherlands

关键词: Atmospheric dynamics;    Low-frequency variability;    Low-order models;    Bifurcations;    Intermittency;    Routes to chaos;   

DOI  :  10.1016/j.physd.2010.02.003

来源: Elsevier

【 摘 要 】

This paper studies the dynamical mechanisms potentially involved in the so-called atmospheric low-frequency variability, occurring at midlatitudes in the Northern Hemisphere This phenomenon is characterised by recurrent non-propagating and temporally persistent flow patterns, with typical spatial and temporal scales of 6000-10000 km and 10-50 days, respectively We study a low-order model derived from the 2-layer shallow-water equations on a beta-plane channel The main ingredients of the low-order model are a zonal flow, a planetary scale wave, orography, and a baroclinic-like forcing A systematic analysis of the dynamics of the low-order model is performed using techniques and concepts from dynamical systems theory Orography height (h(0)) and magnitude of zonal wind forcing (U-0) are used as control parameters to study the bifurcations of equilibria and periodic orbits Along two curves of Hopf bifurcations an equilibrium loses stability (U-0 >= 12 5 m/s) and gives birth to two distinct families of periodic orbits These periodic orbits bifurcate into strange attractors along three routes to chaos period doubling cascades, breakdown of 2-tori by homo- and heteroclinic bifurcations, or intermittency (U-0 >= 14 5 m/s and h(0) >= 800 m) The observed attractors exhibit spatial and temporal low-frequency patterns comparing well with those observed in the atmosphere For h(0) <= 800 m the periodic orbits have a period of about 10 days and patterns in the vorticity field propagate eastward For h(0) >= 800 m, the period is longer (30-60 days) and patterns in the vorticity field are non-propagating. The dynamics on the strange attractors are associated with low-frequency variability the vorticity fields show weakening and strengthening of non-propagating planetary waves on time scales of 10-200 days The spatio-temporal characteristics are inherited (by intermittency) from the two families of periodic orbits and are detected in a relatively large region of the parameter plane This scenario provides a characterisation of low-frequency variability in terms of intermittency due to bifurcations of waves (C) 2010 Elsevier B V All rights reserved

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