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Nicolis C.,Institute Royal Meteorologique Of Belgique | Nicolis G.,The Interdisciplinary Center
Quarterly Journal of the Royal Meteorological Society | Year: 2010

The formalism of irreversible thermodynamics is extended to include the effect of random perturbations and applied to representative systems giving rise to instabilities and to complex nonlinear behaviours. The extent to which dissipation as measured by the entropy production exhibits variational properties that can be linked to key indicators of the dynamical behaviour is explored with emphasis on the conjecture of the climate system as a system of maximum dissipation. © 2010 Royal Meteorological Society. Source

Vannitsem S.,Institute Royal Meteorologique Of Belgique
Climate Dynamics | Year: 2014

The dynamics of a low-order coupled wind-driven ocean-atmosphere system is investigated with emphasis on its predictability properties. The low-order coupled deterministic system is composed of a baroclinic atmosphere for which 12 dominant dynamical modes are only retained (Charney and Straus in J Atmos Sci 37:1157-1176, 1980) and a wind-driven, quasi-geostrophic and reduced-gravity shallow ocean whose field is truncated to four dominant modes able to reproduce the large scale oceanic gyres (Pierini in J Phys Oceanogr 41:1585-1604, 2011). The two models are coupled through mechanical forcings only. The analysis of its dynamics reveals first that under aperiodic atmospheric forcings only dominant single gyres (clockwise or counterclockwise) appear, while for periodic atmospheric solutions the double gyres emerge. In the present model domain setting context, this feature is related to the level of truncation of the atmospheric fields, as indicated by a preliminary analysis of the impact of higher wavenumber ("synoptic" scale) modes on the development of oceanic gyres. In the latter case, double gyres appear in the presence of a chaotic atmosphere. Second the dynamical quantities characterizing the short-term predictability (Lyapunov exponents, Lyapunov dimension, Kolmogorov-Sinaï (KS) entropy) displays a complex dependence as a function of the key parameters of the system, namely the coupling strength and the external thermal forcing. In particular, the KS-entropy is increasing as a function of the coupling in most of the experiments, implying an increase of the rate of loss of information about the localization of the system on its attractor. Finally the dynamics of the error is explored and indicates, in particular, a rich variety of short term behaviors of the error in the atmosphere depending on the (relative) amplitude of the initial error affecting the ocean, from polynomial (at2 + bt3 + ct4) up to exponential-like evolutions. These features are explained and analyzed in the light of the recent findings on error growth (Nicolis et al. in J Atmos Sci 66:766-778, 2009). © 2013 Springer-Verlag Berlin Heidelberg. Source

Vannitsem S.,Institute Royal Meteorologique Of Belgique
Geophysical Research Letters | Year: 2015

The development of the low-frequency variability (LFV) in the atmosphere at multidecadal timescales is investigated in the context of a low-order coupled ocean-atmosphere model designed to emulate the interaction between the ocean mixed layer (OML) and the atmosphere at midlatitudes, both subject to seasonal variations of the Sun's radiative input. When no seasonal dependences are present, a LFV is emerging from the chaotic background for sufficiently large wind stress forcing (WSF). The period of this LFV is strongly controlled by the depth of the OML, with a shorter period for a deeper layer. In the seasonally dependent case, a similar LFV is developing that persists throughout the year. Remarkably, the emergence of this LFV occurs for smaller values of the WSF coefficient and is strongly related to the small thickness of the OML in summer, i.e., large impact of the WSF. Potential implications for real-world dynamics are discussed. Key Points The low-frequency variability at decadal timescales is robust in the presence of a seasonal cycle The summer ocean mixed layer depth plays a key role in the emergence of the LFV The mean depth of the ocean mixed layer controls the period of the low-frequency variability © 2015. American Geophysical Union. All Rights Reserved. Source

Nicolis C.,Institute Royal Meteorologique Of Belgique
Physical Review E - Statistical, Nonlinear, and Soft Matter Physics | Year: 2010

The classical setting of stochastic resonance is extended to account for the presence of an arbitrary number of simultaneously stable steady states. General expressions for the linear response are derived for systems involving one variable. The existence of an optimal value of noise strength and of an optimal number of stable states for which the response is maximized is established. © 2010 The American Physical Society. Source

Nicolis C.,Institute Royal Meteorologique Of Belgique
Physical Review E - Statistical, Nonlinear, and Soft Matter Physics | Year: 2012

The theory of stochastic resonance in multistable systems is extended to account for both direct transitions between all stable states present and indirect ones involving intermediate states. It is shown that to satisfy these requirements the dynamics needs to be embedded in phase spaces of dimension equal to at least two. Under well defined conditions, the conjunction of the presence of intermediate states and the multidimensional character of the process leads to an enhancement of the response of the system to an external periodic forcing. © 2012 American Physical Society. Source

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