This paper represents a novel strategy to improve the scalability of the barotropic mode in the parallel ocean program (POP), by theoretically analyzing the barotropic communications bottleneck. POP discretizes the el...
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ISBN:
(纸本)9783642400476
This paper represents a novel strategy to improve the scalability of the barotropic mode in the parallel ocean program (POP), by theoretically analyzing the barotropic communications bottleneck. POP discretizes the elliptic equations of the barotropic mode into a linear system Ax = b and solves it using the Preconditioned Conjugate Gradient (PCG) method. PCG scales poorly on distributed systems because of the time-consuming global reductions needed by the inner products in each iteration. A performance model is developed to quantify the scaling bottleneck of PCG. Based on this model, the classical Stiefel iteration (CSI), which was originally supposed to be less efficient than PCG, is identified as being promising for massive parallelism. In contrast to PCG, the recurrence parameters of CSI are determined by the spectrum of the coefficient matrix A instead of the inner product of the residuals in previous iterations. The Lanczos method is used to resolve the difficulty of estimating the eigenvalues of the large-scale matrix A. It constructs a small-scale tridiagonal matrix that has eigenvalues close to A. By replacing PCG with CSI, global reductions and their inherent poor scalability are eliminated in the barotropic mode. The implementation of CSI in POP with a 0.1 degree resolution can accerlate one barotropic step by five times, from 1.23s to 0.26s, on 15,000 cores.
The circulation of the Southern ocean is studied in the eddy-resolving model POP (parallel ocean program) by an analysis of zonally integrated balances. The TEM formalism (Transformed Eulerian Mean) is extended to inc...
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The circulation of the Southern ocean is studied in the eddy-resolving model POP (parallel ocean program) by an analysis of zonally integrated balances. The TEM formalism (Transformed Eulerian Mean) is extended to include topography and continental boundaries, thus deviations from a zonally integrated state involve transient and standing eddies. The meridional circulation is presented in terms of the Eulerian, eddy-induced, and residual streamfunctions. It is shown that the splitting of the meridional circulation into Ekman and geostrophic transports and the component induced by subgrid and Reynolds stresses is identical to a particular form of the zonally integrated balance of zonal momentum. In this balance, the eddy-induced streamfunctions represent the interfacial form stresses by transient and standing eddies and the residual streamfunction represents the acceleration of the zonal current by density fluxes in a zonally integrated frame. The latter acceleration term is directly related to the surface flux of density and interior fluxes due to the resolved and unresolved eddies. The eddy-induced circulation is extremely vigorous in POP. In the upper ocean a shallow circulation, reversed in comparison to the Deacon cell and mainly due to standing eddies, appears to the north of Drake Passage latitudes, and in the Drake Passage belt of latitudes a deep-reaching cell is induced by transient eddies. In the resulting residual circulation the Deacon cell is largely cancelled and the residual advection of the zonal mean potential density is balanced by diapycnal eddy and subgrid fluxes which are strong in the upper few hundred meters but small in the ocean interior. The balance of zonal momentum is consistent with other eddy-resolving models;a new aspect is the clear identification of density effects in the zonally integrated balance. We show that the wind stress and the stress induced by the residual circulation drive the eastward current, whereas both eddy species res
Recently, multidecadal variability in the Southern ocean has been found in a strongly eddying global ocean circulation model. In this paper, we study the Lorenz energy cycle of this so-called Southern ocean Mode (SOM)...
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Recently, multidecadal variability in the Southern ocean has been found in a strongly eddying global ocean circulation model. In this paper, we study the Lorenz energy cycle of this so-called Southern ocean Mode (SOM). The Lorenz energy cycle analysis provides details on the energy pathways associated with the SOM. It shows that ocean eddies and the baroclinic energy pathway together with variations in the kinetic energy input by the wind are crucial aspects of the variability. It is also shown how convective mixing, which is induced by the SOM in particular in the Weddell Gyre, is responsible for the large-scale multidecadal variability in Antarctic Bottom Water and Atlantic Meridional Overturning Circulation. Plain Language Summary Recently, large fluctuations of the oceanic heat content were discovered in the Atlantic sector of the Southern ocean in an ocean simulation. These changes are periodic and repeat every 50years, which is why we cannot confirm them from out limited observational record. We investigate this phenomenon through a mechanical energy perspective and find that it is likely caused by an interplay between eddies (the oceanic equivalent of atmospheric storms with 10- to 100-km diameter) and the average flow around Antarctica. In addition, we find connected sinking events that influence the ocean's overturning strength. If this phenomenon is found in the real ocean, it may influence the global mean surface temperature significantly over decades.
The Atlantic Meridional Overturning Circulation (AMOC) responds sensitively to density changes in regions of deepwater formation. In this paper, we investigate the nonlinear response of the AMOC to large amplitude fre...
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The Atlantic Meridional Overturning Circulation (AMOC) responds sensitively to density changes in regions of deepwater formation. In this paper, we investigate the nonlinear response of the AMOC to large amplitude freshwater changes around Greenland using a strongly-eddying global ocean model. Due to a 0.5 Sv freshwater input, the maximum AMOC at 35 degrees N decreases by about 50% over a 45 year period. The AMOC does not recover over a period of 50 years when the freshwater input is ceased at year 45. However, when reversing the sign of the freshwater input at year 45, the AMOC needs only about 10 years to fully recover. The mechanism that causes this asymmetric response in theAMOC is clarified using water mass transformation theory.
Quantitative analysis of the failures and crashes in simulation of climate models can yield useful insights to better understanding and improvement of the models results using Intergovernmental Panel on Climate Change...
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Quantitative analysis of the failures and crashes in simulation of climate models can yield useful insights to better understanding and improvement of the models results using Intergovernmental Panel on Climate Change (IPCC) class. In this paper, the authors propose a new technique inspired by termite's hill building behavior to analyze a series of simulation in climate models and predict which one was succeeded within the parallel ocean program (POP2) component of the community Climate System Model (CCSM4). The authors' approach is a distance based approach used to predict the success of the values of 18 POP2 parameters. And in order to predict better results, they used for each experiment one of the studies as a training set and two as a test set, then they used two of the studies as a training set and one as a test set. Results of classification were very satisfactory (Accuracy > 0.87). This paper gives a very useful method to quantify, predict, and understand simulation success in climate models.
There are many large scientific applications that have been actively developed for several decades. However, in this time the hardware has evolved considerably. It is taking large scientific applications a very long t...
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ISBN:
(纸本)9781467393256
There are many large scientific applications that have been actively developed for several decades. However, in this time the hardware has evolved considerably. It is taking large scientific applications a very long time to get adjusted to the new computing infrastructure. This is because porting these applications to new hardware, such as Graphics Processing Units (GPUs), currently requires a huge amount of manual labor, even though the computations are very well suited for GPUs. In this paper we propose an integrated approach to semi-automatically port large long-lived scientific codes to GPUs. We propose a method that considerably reduces the effort required by experienced GPU programmers to port these applications. This approach is supported by a tool that is able to analyze, transform, and translate source code into different programming languages. We evaluate our approach by applying it to the parallel ocean program, a representative, very large, and widely-used scientific application.
The study focuses on determining whether there are any crashes or failure that are associated with the use of climate models when its parameters are induced to simulation. The study also focuses on analysing condition...
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The study focuses on determining whether there are any crashes or failure that are associated with the use of climate models when its parameters are induced to simulation. The study also focuses on analysing conditions that can cause climate models to fail because climate models are prone to failure, it become an important to determine chances of failure of the moodels. For this purpose in this thesis the neuro-fuzzy models is designed to determine chances of failure of the models. Consequently the aim was to develop solutions can be used to enhance the success or usefulness of models. The study used Takagi-Sugeno-Kang (TSK) type fuzzy rules for conducting neuro- fuzzy model which was used in simulation of climate crashes. For comparative analysis Support Vector Machines (SVM) is applied for simulation of the same problem. SVM is modelled using LibSVM package. A comparison was made between SVM and neuro-fuzzy model results to determine which algorithm offers the best simulation results. Accuracy rates of 94.4% and 95.55% were obtained for SVM and neuro-fuzzy model of the simulations. However, the neuro-fuzzy model was discovered to be having better performance in modelling climate crashes. Observations were also made that the POP2 of the CCSM4 was characterised with simulation failures. Research findings revealed that numerical reasons accounted for 8.5% of the simulation failures.
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