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Optimal nonlinear excitation of decadal variability of the North Atlantic thermohaline circulation

Chinese Journal of Oceanology and Limnology 2013年第6期31卷 1356-1362页

作者：祖子清穆穆 henk a.dijkstra LASG Institute of Atmospheric PhysicsChinese Academy of Sciences University of Chinese Academy of Sciences Key Laboratory of Ocean Circulation and Wave Institute of OceanologyChinese Academy of Sciences Institute for Marine and Atmospheric Research Utrecht Department of Physics and AstronomyUtrecht University

Nonlinear development of salinity perturbations in the Atlantic thermohaline circulation(THC) is investigated with a three-dimensional ocean circulation model,using the conditional nonlinear optimal perturbation *** results show two types of optimal initial perturbations of sea surface salinity,one associated with freshwater and the other with *** types of perturbations excite decadal variability of the *** the same amplitude of initial perturbation,the decadal variation induced by the freshwater perturbation is much stronger than that by the salinity perturbation,suggesting that the THC is more sensitive to freshwater than salinity *** the amplitude of initial perturbation increases,the decadal variations become stronger for both *** salinity perturbations,recovery time of the THC to return to steady state gradually saturates with increasing amplitude,whereas this recovery time increases remarkably for freshwater perturbations.A nonlinear(advective) feedback between density and velocity anomalies is proposed to explain these characteristics of decadal variability *** results are consistent with previous ones from simple box models,and highlight the importance of nonlinear feedback in decadal THC variability.

关键词： thermohaline circulation decadal variability conditional nonlinear optimal perturbation nonlinear advective feedback

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Application of the Conditional Nonlinear Optimal Perturbation Method to the Predictability Study of the Kuroshio Large Meander

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Advances in Atmospheric Sciences 2012年第1期29卷 118-134页

作者： WANG Qiang MU Mu henk a.dijkstra State Key Laboratory of Numerical Modeling for Atmospheric Sciences and Geophysical Fluid Dynamics Institute of Atomspheric PhysicsChinese Academy of SciencesBeijing 100029 Graduate University of the Chinese Academy of Sciences Beijing 100049 Key Laboratory of Ocean Circulation and Wave Institute of OceanologyChinese Academy of SciencesQingdao 266071 Institute for Marine and Atmospheric Research Utrecht Department of Physics and AstronomyUtrecht University3584 CC Utrechtthe Netherlands

A reduced-gravity barotropic shallow-water model was used to simulate the Kuroshio path variations. The results show that the model was able to capture the essential features of these path variations. We used one simulation of the model as the reference state and investigated the effects of errors in model parameters on the prediction of the transition to the Kuroshio large meander （KLM） state using the conditional nonlinear optimal parameter perturbation （CNOP-P） method. Because of their relatively large uncertainties, three model parameters were considered： the interracial friction coefficient, the wind-stress amplitude, and the lateral friction coefficient. We determined the CNOP-Ps optimized for each of these three parameters independently, and we optimized all three parameters simultaneously using the Spectral Projected Gradient 2 （SPG2） algorithm. Similarly, the impacts caused by errors in initial conditions were examined using the conditional nonlinear optimal initial perturbation （CNOP-I） method. Both the CNOP-I and CNOP-Ps can result in significant prediction errors of the KLM over a lead time of 240 days. But the prediction error caused by CNOP-I is greater than that caused by CNOP-P. The results of this study indicate not only that initial condition errors have greater effects on the prediction of the KLM than errors in model parameters but also that the latter cannot be ignored. Hence, to enhance the forecast skill of the KLM in this model, the initial conditions should first be improved, the model parameters should use the best possible estimates.

关键词： conditional nonlinear optimal perturbation Kuroshio large meander predictability model parameters

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Three-Dimensional Structure of Optimal Nonlinear Excitation for Decadal Variability of the Thermohaline Circulation

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Atmospheric and Oceanic Science Letters 2013年第6期6卷 410-416页

作者： ZU Zi-Qing MU Mu henk a.dijkstra State Key Laboratory of Numerical Modeling for Atmospheric Sciences and Geophysical Fluid Dynamics (LASG) Institute of Atmospheric Physics Chinese Academy of Sciences University of Chinese Academy of Sciences Key Laboratory of Ocean Circulation and Wave Institute of Oceanology Chinese Academy of Sciences Institute for Marine and Atmospheric Research Utrecht Department of Physics and Astronomy Utrecht University

The decadal variability of the North Atlantic thermohaline circulation(THC) is investigated within a three-dimensional ocean circulation model using the conditional nonlinear optimal perturbation method. The results show that the optimal initial perturbations of temperature and salinity exciting the strongest decadal THC variations have similar structures: the perturbations are mainly in the northwestern basin at a depth ranging from 1500 to 3000 m. These temperature and salinity perturbations act as the optimal precursors for future modifications of the THC, highlighting the importance of observations in the northwestern basin to monitor the variations of temperature and salinity at depth. The decadal THC variation in the nonlinear model initialized by the optimal salinity perturbations is much stronger than that caused by the optimal temperature perturbations, indicating that salinity variations might play a relatively important role in exciting the decadal THC variability. Moreover, the decadal THC variations in the tangent linear and nonlinear models show remarkably different characteristics, suggesting the importance of nonlinear processes in the decadal variability of the THC.

关键词： thermohaline circulation decadal variability conditional nonlinear optimal perturbation optimal precursor nonlinear processes

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Numerical Bifurcation Methods and their Application to Fluid Dynamics: Analysis beyond Simulation

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Communications in Computational Physics 2014年第1期15卷 1-45页

作者： henk a.dijkstra Fred W.Wubs Andrew K.Cliffe Eusebius Doedel Ioana F.Dragomirescu Bruno Eckhardt Alexander Yu.Gelfgat Andrew L.Hazel Valerio Lucarini Andy G.Salinger Erik T.Phipps Juan Sanchez-Umbria henk Schuttelaars Laurette S.Tuckerman Uwe Thiele Institute for Marine and Atmospheric Research Utrecht Utrecht UniversityThe Netherlands. Department of Mathematics and Computer Science University of GroningenGroningenThe Netherlands. School of Mathematical Sciences University of NottinghamNottinghamUK Department of Computer Science Concordia UniversityMontrealCanada. National Centre for Engineering Systems of Complex Fluids University Politehnica of TimisoaraRomania. Fachbereich Physik Philipps-Universitat MarburgMarburgGermany. School of Mechanical Engineering Faculty of EngineeringTel-Aviv UniversityTel-AvivIsrael. School of Mathematics University of ManchesterManchesterUK. Meteorological Institute KlimacampusUniversity of HamburgHamburgGermany. Department of Mathematics and Statistics University of ReadingReadingUK. Sandia National Laboratories AlbuquerqueUSA. Departament de Fisica Aplicada Universitat Politecnica de CatalunyaBarcelonaSpain. Department of Applied Mathematical Analysis TU DelftDelftthe Netherlands. PMMH-ESPCI ParisFrance. Department of Mathematical Sciences Loughborough UniversityLoughboroughUK.

We provide an overview of current techniques and typical applications of numerical bifurcation analysis in fluid dynamical *** of these problems are characterized by high-dimensional dynamical systems which undergo transitions as parameters are *** computation of the critical conditions associated with these transitions,popularly referred to as‘tipping points’,is important for understanding the transition *** describe the two basic classes of methods of numerical bifurcation analysis,which differ in the explicit or implicit use of the Jacobian matrix of the dynamical *** numerical challenges involved in both methods are mentioned and possible solutions to current bottlenecks are *** demonstrate that numerical bifurcation techniques are not restricted to relatively low-dimensional dynamical systems,we provide several examples of the application of the modern techniques to a diverse set of fluid mechanical problems.

关键词： Numerical bifurcation analysis transitions in fluid flows high-dimensional dynamical systems.

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