IN MEMORIAM     

Trond Iversen  Sigbjørn Grønås 《地球，A辑:动力气象学与海洋学》2004,56(4):271-272

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States of maximum entropy production in a one-dimensional vertical model with convective adjustment   总被引：2，自引：0，他引：2  

By TONI PUJOL  JOAQUIM FORT 《地球，A辑:动力气象学与海洋学》2002,54(4):363-369

We investigate the hypothesis that the atmosphere is constrained to maximize its entropy production by using a one-dimensional (1-D) vertical model. We prescribe the lapse rate in the convective layer as that of the standard troposphere. The assumption that convection sustains a critical lapse rate was absent in previous studies, which focused on the vertical distribution of climatic variables, since such a convective adjustment reduces the degrees of freedom of the system and may prevent the application of the maximum entropy production (MEP) principle. This is not the case in the radiative-convective model (RCM) developed here, since we accept a discontinuity of temperatures at the surface similar to that adopted in many RCMs.
For current conditions, the MEP state gives a difference between the ground temperature and the air temperature at the surface ≈10 K. In comparison, conventional RCMs obtain a discontinuity ≈2K only. However, the surface boundary layer velocity in the MEP state appears reasonable (≈m s⁻¹). Moreover, although the convective flux at the surface in MEP states is almost uniform in optically thick atmospheres, it reaches a maximum value for an optical thickness similar to current conditions. This additional result may support the maximum convection hypothesis suggested by Paltridge (1978 ).  相似文献   

Reservoir description using dynamic parameterisation selection with a combined stochastic and gradient search     

Lars Kristian Nielsen  Sam Subbey  Mike Christie  Trond Mannseth 《Computational Geosciences》2006,10(3):321-342

There is a correspondence between flow in a reservoir and large scale permeability trends. This correspondence can be derived by constraining reservoir models using observed production data. One of the challenges in deriving the permeability distribution of a field using production data involves determination of the scale of resolution of the permeability. The Adaptive Multiscale Estimation (AME) seeks to overcome the problems related to choosing the resolution of the permeability field by a dynamic parameterisation selection. The standard AME uses a gradient algorithm in solving several optimisation problems with increasing permeability resolution. This paper presents a hybrid algorithm which combines a gradient search and a stochastic algorithm to improve the robustness of the dynamic parameterisation selection. At low dimension, we use the stochastic algorithm to generate several optimised models. We use information from all these produced models to find new optimal refinements, and start out new optimisations with several unequally suggested parameterisations. At higher dimensions we change to a gradient-type optimiser, where the initial solution is chosen from the ensemble of models suggested by the stochastic algorithm. The selection is based on a predefined criterion. We demonstrate the robustness of the hybrid algorithm on sample synthetic cases, which most of them were considered insolvable using the standard AME algorithm.  相似文献   

Large igneous provinces generated from the margins of the large low-velocity provinces in the deep mantle     

Trond H. Torsvik  Mark A. Smethurst  Kevin Burke  Bernhard Steinberger 《Geophysical Journal International》2006,167(3):1447-1460

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Permeability Estimation with the Augmented Lagrangian Method for a Nonlinear Diffusion Equation     

Trygve K. Nilssen  Trond Mannseth  Xue-Cheng Tai 《Computational Geosciences》2003,7(1):27-47

We consider numerical identification of the piecewise constant permeability function in a nonlinear parabolic equation, with the augmented Lagrangian method. By studying this problem, we aim at also gaining some insight into the potential ability of the augmented Lagrangian method to handle permeability estimation within the full two-phase porous-media flow setting. The identification is formulated as a constrained minimization problem. The parameter estimation problem is reduced to a coupled nonlinear algebraic system, which can be solved efficiently with the conjugate gradient method. The methodology is developed and numerical experiments with the proposed method are presented.  相似文献   

Rob Van der Voo—an appreciation     

Conall Mac Niocaill  Trond Torsvik  Ben van der Pluijm 《Tectonophysics》2003,362(1-4):xi-xii

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Adaptive Multiscale Permeability Estimation     

Alv-Arne Grimstad  Trond Mannseth  Geir Nævdal  Hege Urkedal 《Computational Geosciences》2003,7(1):1-25

With multiscale permeability estimation one does not select parameterization prior to the estimation. Instead, one performs a hierarchical search for the right parameterization while solving a sequence of estimation problems with an increasing parameterization dimension. In some previous works on the subject, the same refinement is applied all over the porous medium. This may lead to over-parameterization, and subsequently, to unrealistic permeability estimates and excessive computational work. With adaptive multiscale permeability estimation, the new parameterization at an arbitrary stage in the estimation sequence is such that new degrees of freedom are not necessarily introduced all over the porous medium. The aim is to introduce new degrees of freedom only where it is warranted by the data. In this paper, we introduce a novel adaptive multiscale estimation. The approach is used to estimate absolute permeability from two-phase pressure data in several numerical examples.  相似文献   

A multi-dimensional assessment of urban vulnerability to climate change in Sub-Saharan Africa     

Lise Byskov Herslund  Fatemeh Jalayer  Nathalie Jean-Baptiste  Gertrud Jørgensen  Sigrun Kabisch  Wilbard Kombe  Sarah Lindley  Patrik Karlsson Nyed  Stephan Pauleit  Andreas Printz  Trond Vedeld 《Natural Hazards》2016,82(2):149-172

In this paper, we develop and apply a multi-dimensional vulnerability assessment framework for understanding the impacts of climate change-induced hazards in Sub-Saharan African cities. The research was carried out within the European/African FP7 project CLimate change and Urban Vulnerability in Africa, which investigated climate change-induced risks, assessed vulnerability and proposed policy initiatives in five African cities. Dar es Salaam (Tanzania) was used as a main case with a particular focus on urban flooding. The multi-dimensional assessment covered the physical, institutional, attitudinal and asset factors influencing urban vulnerability. Multiple methods were applied to cover the full range of vulnerabilities and to identify potential response strategies, including: model-based forecasts, spatial analyses, document studies, interviews and stakeholder workshops. We demonstrate the potential of the approach to assessing several dimensions of vulnerability and illustrate the complexity of urban vulnerability at different scales: households (e.g., lacking assets); communities (e.g., situated in low-lying areas, lacking urban services and green areas); and entire cities (e.g., facing encroachment on green and flood-prone land). Scenario modeling suggests that vulnerability will continue to increase strongly due to the expected loss of agricultural land at the urban fringes and loss of green space within the city. However, weak institutional commitment and capacity limit the potential for strategic coordination and action. To better adapt to urban flooding and thereby reduce vulnerability and build resilience, we suggest working across dimensions and scales, integrating climate change issues in city-level plans and strategies and enabling local actions to initiate a ‘learning-by-doing’ process of adaptation.  相似文献   

Climate adaptation at what scale? Multi-level governance,resilience, and coproduction in Saint Louis,Senegal     

Trond Vedeld  Adrien Coly  Ndèye Marème Ndour  Siri Hellevik 《Natural Hazards》2016,82(2):173-199

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Large-scale atmospheric circulation changes are associated with the recent loss of Arctic sea ice   总被引：21，自引：0，他引：21  

By JAMES E. OVERLAND  MUYIN WANG 《地球，A辑:动力气象学与海洋学》2010,62(1):1-9

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