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The Parthenope University of Naples is one of the universities located in Naples, Italy. Wikipedia.

Pierini S.,Parthenope University of Naples
Journal of Physical Oceanography | Year: 2011

In this paper, a low-order spectral quasigeostrophic (QG) model of the wind-driven ocean circulation is derived and used to analyze the low-order character of the intrinsic low-frequency variability of the midlatitude double-gyre ocean circulation and of the related coherence resonance and phase selection phenomena. The model includes an exponential in the basis functions that allows for westward intensification, retains only four modes in the Galerkin projection, is defined in a rectangular domain, and is forced by deterministic and stochastic winds, thus extending previous low-order QG ocean models. The solution under steady forcing is first obtained, and the results are also analyzed in terms of dynamical systems theory. A homoclinic bifurcation (with the wind amplitude chosen as the control parameter) leads to intrinsic decadal relaxation oscillations (ROs) similar in several respects to those obtained with primitive equation models. The system is then forced with an additional red noise wind, and, in a parameter range preceding the global bifurcation, a coherence resonance scenario very similar to the one found with a primitive equation model of the Kuroshio Extension is obtained: this suggests that such a phenomenon is of low-order character. To study the RO excitation mechanism, a method denoted as phase selection is proposed. The system is forced with additional fictitious periodic winds that produce an emergence of ROs yielding strong phase dependence with the periodic forcing. The subsequent analysis reveals the character of the wind forcing that is most likely to excite a RO. All the results are discussed within the general framework of climate dynamics. © 2011 American Meteorological Society.

A previous North Pacific Ocean circulation model forced by climatological winds is extended here to include a time-dependent North Pacific Oscillation (NPO) forcing. The Kuroshio Extension (KE) decadal bimodal cycle (which is a self-sustained intrinsic relaxation oscillation in the climatologically forced case) is now excited by the NPO forcing. Both the timing of the cycles and the Rossby wave teleconnection mechanism that is found to govern the synchronization from 1993 to 2012 are in good agreement with altimeter observations. Sensitivity numerical experiments are carried out by varying the zonal location and amplitude of the NPO forcing, and the lateral eddy viscosity. The emergence of the KE bimodality with a correct timing is found to be extremely sensitive to changes in the dissipative parameterization; the implications of such sensitivity for deficiencies found in more realistic North Pacific Ocean general circulation models are discussed. The dynamical mechanism that emerges from this study is explained as a case of intrinsic variability in an excitable dynamical system triggered, and therefore paced, by an external forcing. © 2014 American Meteorological Society.

Sapio A.,Parthenope University of Naples
Energy Policy | Year: 2015

Renewable energy production can exercise a downward pressure on electricity prices by partly crowding out conventional units characterized by higher marginal costs (merit order effect). Yet, congestion induced by renewables would partly offset the merit order effect in the congested zone, unless renewables reduce the need for imports and allow the emergence of prosumers. These congestion effects of renewables are hereby jointly tested with the merit order effect by means of an endogenous regime-switching model wherein a regime corresponds to the observable status (congested/non-congested) of the grid. The model is taken to data from the Italian power exchange, observed in 2012 and 2013, with a focus on the line connecting Sicily with the South zone, a frequent bottleneck in the Italian transmission grid. The results confirm the merit order effect previously detected in the literature and highlight a negative congestion effect, i.e. renewables relieve congestion from Sicily, a systematic importer, but not from the Italian peninsula (the exporting region). This effect is mainly driven by the wind power in-feed. © 2015 Elsevier Ltd.

Pierini S.,Parthenope University of Naples
Journal of Physical Oceanography | Year: 2010

The effect of stochastic winds on the intrinsic low-frequency variability of the Kuroshio Extension (KE) is analyzed through a double-gyre (DG)model forced by a steady climatological wind plus an idealized Ornstein-Uhlenbeck wind noise. A DG model of the KE bimodality, whose results compare well to altimeter data, is first shown to be an excitable system. In fact, the relaxation oscillation (forced by steady winds) with decadal time scale that describes the bimodality is recognized to be an internal mode of the system, which can be excited also in a dissipative parameter range (PR) in which it does not arise spontaneously, provided appropriate initial conditions are chosen. It is then shown that, if the additive wind noise is included in the forcing, the actual excitation of the relaxation oscillation in PR occurs if the noise is red with a decorrelation time greater than a minimum time scale ranging from 1 month to 1 year, depending on the dissipation. This behavior, known as "coherence resonance," is likely to be paradigmatic of the low-frequency variability of western boundary current extensions of intrinsic origin, when it is in the form of relaxation oscillations resulting from a homoclinic bifurcation. General considerations concerning the interpretation of model results obtained within different parameter ranges are applied to this study. © 2010 American Meteorological Society.

Pierini S.,Parthenope University of Naples
Physical Review E - Statistical, Nonlinear, and Soft Matter Physics | Year: 2012

A crucial question recently raised in climate dynamics concerns abrupt climate transitions: Are they due to a tipping point (TP) being exceeded, or is fast noisy dynamics the cause of their excitation? In this respect, a case study based on a low-order ocean model is developed to show that in an excitable dynamical system perturbed by noise (a possible climate condition) the TPs may have limited physical meaning, with the coherence resonance mechanism being predominant. The analysis is based on an operational definition of stochastic TP, which accounts for the effect of noise and reconciles formally the TP and coherence resonance views. © 2012 American Physical Society.

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