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Control simulation experiments of extreme events with the Lorenz-96 model Lorenz-96模型对极端事件的控制模拟实验
IF 2.2 4区 地球科学 Q3 GEOSCIENCES, MULTIDISCIPLINARY Pub Date : 2023-06-19 DOI: 10.5194/npg-30-117-2023
Q. Sun, T. Miyoshi, S. Richard
Abstract. The control simulation experiment (CSE) is a recently developed approach to investigate the controllability of dynamical systems,extending the well-known observing system simulation experiment (OSSE) in meteorology.For effective control of chaotic dynamical systems,it is essential to exploit the high sensitivity to initial conditions for dragging a system away from an undesired regime by applying minimal perturbations.In this study, we design a CSE for reducing the number of extreme events in the Lorenz-96 model. The 40 variables of this model represent idealized meteorological quantities evenly distributed on a latitude circle.The reduction of occurrence of extreme events over 100-year runs of the model is discussed as a function of the parameters of the CSE:the ensemble forecast length for detecting extreme events in advance,the magnitude and localization of the perturbations,and the quality and coverage of the observations.The design of the CSE is aimed at reducing weather extremes when applied to more realistic weather prediction models.
摘要控制模拟实验(CSE)是近年来发展起来的一种研究动力系统可控性的方法,扩展了气象学中著名的观测系统模拟实验(OSSE)。为了有效控制混沌动力系统,必须利用对初始条件的高灵敏度,通过施加最小扰动将系统从不期望的状态拖走。在这项研究中,我们设计了一个CSE来减少Lorenz-96模型中的极端事件数量。该模型的40个变量代表了均匀分布在纬度圈上的理想气象量。在该模型的100年运行中,极端事件发生率的减少被讨论为CSE参数的函数:提前检测极端事件的集合预测长度、扰动的大小和定位,以及观测的质量和覆盖范围。CSE的设计目的是在应用于更现实的天气预测模型时减少极端天气。
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引用次数: 1
Exploring meteorological droughts' spatial patterns across Europe through complex network theory 通过复杂网络理论探索欧洲各地的气象干旱空间模式
IF 2.2 4区 地球科学 Q3 GEOSCIENCES, MULTIDISCIPLINARY Pub Date : 2023-06-15 DOI: 10.5194/npg-30-167-2023
Domenico Giaquinto, W. Marzocchi, Jürgen Kurths
Abstract. In this paper we investigate the spatial patterns and features of meteorological droughts in Europe using concepts and methods derived from complexnetwork theory. Using event synchronization analysis, we uncover robust meteorological drought continental networks based on the co-occurrence ofthese events at different locations within a season from 1981 to 2020 and compare the results for four accumulation periods of rainfall. Eachcontinental network is then further examined to unveil regional clusters which are characterized in terms of droughts' geographical propagation andsource–sink systems. While introducing new methodologies in general climate network reconstruction from raw data, our approach brings out keyaspects concerning drought spatial dynamics, which could potentially support droughts' forecast.
摘要本文利用复杂网络理论中的概念和方法,研究了欧洲气象干旱的空间格局和特征。使用事件同步分析,我们基于1981年至2020年一个季节内不同地点同时发生的这些事件,揭示了稳健的气象干旱大陆网络,并比较了四个降雨累积期的结果。然后,进一步研究各大陆网络,以揭示以干旱的地理传播和源汇系统为特征的区域集群。在从原始数据中引入一般气候网络重建的新方法的同时,我们的方法提出了有关干旱空间动力学的关键方面,这可能支持干旱的预测。
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引用次数: 0
Toward a multivariate formulation of the parametric Kalman filter assimilation: application to a simplified chemical transport model 参数卡尔曼滤波同化的多元公式:在简化化学迁移模型中的应用
IF 2.2 4区 地球科学 Q3 GEOSCIENCES, MULTIDISCIPLINARY Pub Date : 2023-06-14 DOI: 10.5194/npg-30-139-2023
Antoine Perrot, O. Pannekoucke, V. Guidard
Abstract. This contribution explores a new approach to forecasting multivariate covariances for atmospheric chemistry through the use of the parametric Kalman filter (PKF). In the PKF formalism, the error covariance matrix is modellized by a covariance model relying on parameters, for which the dynamics are then computed. The PKF has been previously formulated in univariate cases, and a multivariate extension for chemical transport models is explored here. This contribution focuses on the situation where the uncertainty is due to the chemistry but not due to the uncertainty of the weather. To do so, a simplified two-species chemical transport model over a 1D domain is introduced, based on the non-linear Lotka–Volterra equations, which allows us to propose a multivariate pseudo covariance model. Then, the multivariate PKF dynamics are formulated and their results are compared with a large ensemble Kalman filter (EnKF) in several numerical experiments. In these experiments, the PKF accurately reproduces the EnKF. Eventually, the PKF is formulated for a more complex chemical model composed of six chemical species (generic reaction set). Again, the PKF succeeds at reproducing the multivariate covariances diagnosed on the large ensemble.
摘要这一贡献探索了一种通过使用参数卡尔曼滤波器(PKF)预测大气化学多元协变的新方法。在PKF形式中,误差协方差矩阵通过依赖于参数的协方差模型进行建模,然后计算其动力学。PKF先前已在单变量情况下进行了公式化,并在此探索了化学迁移模型的多变量扩展。这篇文章的重点是不确定性是由化学因素引起的,而不是由天气的不确定性引起的。为此,基于非线性Lotka–Volterra方程,引入了一维域上的简化两物种化学迁移模型,使我们能够提出一个多元伪协方差模型。然后,建立了多元PKF动力学方程,并将其结果与几个数值实验中的大集合卡尔曼滤波器(EnKF)进行了比较。在这些实验中,PKF准确地再现了EnKF。最终,PKF被公式化为一个由六种化学物质组成的更复杂的化学模型(通用反应集)。同样,PKF成功地再现了在大集合上诊断的多变量协变量。
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引用次数: 1
Data-driven reconstruction of partially observed dynamical systems 部分观测动力系统的数据驱动重构
IF 2.2 4区 地球科学 Q3 GEOSCIENCES, MULTIDISCIPLINARY Pub Date : 2023-06-09 DOI: 10.5194/npg-30-129-2023
P. Tandeo, P. Ailliot, F. Sévellec
Abstract. The state of the atmosphere, or of the ocean, cannot be exhaustively observed. Crucial parts might remain out of reach of proper monitoring. Also, defining the exact set of equations driving the atmosphere and ocean is virtually impossible because of their complexity. The goal of this paper is to obtain predictions of a partially observed dynamical system without knowing the model equations. In this data-driven context, the article focuses on the Lorenz-63 system, where only the second and third components are observed and access to the equations is not allowed. To account for those strong constraints, a combination of machine learning and data assimilation techniques is proposed. The key aspects are the following: the introduction of latent variables, a linear approximation of the dynamics and a database that is updated iteratively, maximizing the likelihood. We find that the latent variables inferred by the procedure are related to the successive derivatives of the observed components of the dynamical system. The method is also able to reconstruct accurately the local dynamics of the partially observed system. Overall, the proposed methodology is simple, is easy to code and gives promising results, even in the case of small numbers of observations.
摘要大气层或海洋的状态无法详尽地观察到。关键部分可能仍然无法得到适当的监测。此外,由于其复杂性,几乎不可能定义驱动大气和海洋的精确方程组。本文的目标是在不知道模型方程的情况下获得部分观测到的动力系统的预测。在这种数据驱动的背景下,本文重点关注Lorenz-63系统,其中只观察到第二和第三个分量,并且不允许访问方程。为了解决这些强大的约束,提出了一种将机器学习和数据同化技术相结合的方法。关键方面如下:引入潜在变量,对动力学进行线性近似,并迭代更新数据库,最大限度地提高可能性。我们发现,通过该过程推断的潜在变量与动力学系统的观测分量的连续导数有关。该方法还能够准确地重建部分观测系统的局部动力学。总的来说,所提出的方法简单,易于编码,即使在少量观测的情况下也能给出有希望的结果。
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引用次数: 1
On parameter bias in earthquake sequence models using data assimilation 利用资料同化的地震序列模型中的参数偏差
IF 2.2 4区 地球科学 Q3 GEOSCIENCES, MULTIDISCIPLINARY Pub Date : 2023-04-05 DOI: 10.5194/npg-30-101-2023
A. Banerjee, Ylona van Dinther, F. Vossepoel
Abstract. The feasibility of physics-based forecasting of earthquakes depends on how well models can be calibrated to represent earthquake scenarios givenuncertainties in both models and data. We investigate whether data assimilation can estimate current and future fault states, i.e., slip rate andshear stress, in the presence of a bias in the friction parameter. We perform state estimation as well as combined state-parameter estimation usinga sequential-importance resampling particle filter in a zero-dimensional (0D) generalization of the Burridge–Knopoff spring–block model with rate-and-statefriction. Minor changes in the friction parameter ϵ can lead to different state trajectories and earthquake characteristics. Theperformance of data assimilation with respect to estimating the fault state in the presence of a parameter bias in ϵ depends on the magnitude of thebias. A small parameter bias in ϵ (+3 %) can be compensated for very well using state estimation (R2 = 0.99), whereas anintermediate bias (−14 %) can only be partly compensated for using state estimation (R2 = 0.47). When increasing particle spread by accounting for model error andan additional resampling step, R2 increases to 0.61. However, when there is a large bias (−43 %) in ϵ, only state-parameterestimation can fully account for the parameter bias (R2 = 0.97). Thus, simultaneous state and parameter estimation effectively separates theerror contributions from friction and shear stress to correctly estimate the current and future shear stress and slip rate. This illustrates thepotential of data assimilation for the estimation of earthquake sequences and provides insight into its application in other nonlinear processes withuncertain parameters.
摘要基于物理的地震预报的可行性取决于在模型和数据都存在不确定性的情况下,模型能在多大程度上被校准以代表地震情景。我们研究数据同化是否可以估计当前和未来的断层状态,即滑移率和剪切应力,在存在摩擦参数偏差的情况下。我们在具有速率和状态摩擦的Burridge-Knopoff弹簧块模型的零维(0D)泛化中使用顺序重要性重采样粒子滤波器进行状态估计以及组合状态参数估计。摩擦参数的微小变化会导致不同的状态轨迹和地震特征。在存在参数偏差的情况下,数据同化在估计故障状态方面的性能取决于偏差的大小。使用状态估计(R2 = 0.99)可以很好地补偿小的参数偏差(+ 3%),而使用状态估计只能部分补偿中间偏差(- 14%)(R2 = 0.47)。当考虑到模型误差和额外的重采样步骤增加粒子扩散时,R2增加到0.61。然而,当ε存在较大偏差(- 43%)时,只有状态参数估计才能完全解释参数偏差(R2 = 0.97)。因此,同时状态和参数估计有效地分离了摩擦和剪切应力的误差贡献,以正确估计当前和未来的剪切应力和滑移率。这说明了数据同化对地震序列估计的潜力,并为其在其他具有不确定参数的非线性过程中的应用提供了见解。
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引用次数: 0
Physically Constrained Covariance Inflation from Location Uncertainty 位置不确定性的物理约束协方差膨胀
IF 2.2 4区 地球科学 Q3 GEOSCIENCES, MULTIDISCIPLINARY Pub Date : 2023-03-09 DOI: 10.13140/rg.2.2.18433.53603
Yicun Zhen, Valentin Resseguier, Bertrand Chapron
Abstract. Motivated by the concept of "location uncertainty", initially introduced in Mémin (2014), a scheme is sought to perturb the "location" of a state variable at every forecast time step. Further considering Brenier's theorem Brenier (1991), asserting that the difference of two positive density fields on the same domain can be represented by a transportation map, perturbations are demonstrated to consistently define a SPDE from the original PDE. It ensues that certain quantities, up to the user, are conserved at every time step. Remarkably, derivations following both the SALT Holm (2015) and LU Mémin (2014); 5 Resseguier et al. (2016) settings, can be recovered from this perturbation scheme. Still, it opens broader applicability since it does not explicitly rely on Lagrangian mechanics or Newton's laws of force. For illustration, a stochastic version of the thermal shallow water equation is presented.
摘要。在“位置不确定性”概念的激励下,最初在msammin(2014)中引入,寻求一种方案来扰动状态变量在每个预测时间步长的“位置”。进一步考虑Brenier定理,Brenier(1991)断言同一域上两个正密度场的差可以用运输图表示,证明了扰动可以一致地从原始PDE定义SPDE。结果是,在每个时间步上,一定数量的量(由用户决定)是守恒的。值得注意的是,SALT Holm(2015)和LU m闵(2014)的衍生;5 Resseguier et al.(2016)设置,可以从这个摄动方案中恢复。尽管如此,由于它不明确地依赖于拉格朗日力学或牛顿的力定律,它具有更广泛的适用性。为了说明,给出了一个随机版本的浅水热方程。
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引用次数: 0
A range of outcomes: the combined effects of internal variability and anthropogenic forcing on regional climate trends over Europe 一系列结果:内部变化和人为作用力对欧洲区域气候趋势的综合影响
IF 2.2 4区 地球科学 Q3 GEOSCIENCES, MULTIDISCIPLINARY Pub Date : 2023-02-15 DOI: 10.5194/npg-30-63-2023
C. Deser, A. Phillips
Abstract. Disentangling the effects of internal variability and anthropogenic forcing on regional climate trends remains a key challenge with far-reaching implications. Due to its largely unpredictable nature on timescales longer than a decade, internal climate variability limits the accuracy of climate model projections, introduces challenges in attributing past climate changes, and complicates climate model evaluation. Here, we highlight recent advances in climate modeling and physical understanding that have led to novel insights about these key issues. In particular, we synthesize new findings from large-ensemble simulations with Earth system models, observational large ensembles, and dynamical adjustment methodologies, with a focus on European climate.
摘要解开内部变率和人为强迫对区域气候趋势的影响仍然是一个具有深远影响的关键挑战。由于其在超过十年的时间尺度上的不可预测性,内部气候变率限制了气候模式预估的准确性,给过去气候变化的归因带来了挑战,并使气候模式的评估复杂化。在这里,我们强调了气候模拟和物理理解方面的最新进展,这些进展导致了对这些关键问题的新见解。特别是,我们将大集合模拟的新发现与地球系统模式、观测大集合和动力调整方法综合起来,重点关注欧洲气候。
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引用次数: 7
Extending ensemble Kalman filter algorithms to assimilate observations with an unknown time offset 扩展集合卡尔曼滤波算法以同化具有未知时间偏移的观测
IF 2.2 4区 地球科学 Q3 GEOSCIENCES, MULTIDISCIPLINARY Pub Date : 2023-02-07 DOI: 10.5194/npg-30-37-2023
Elia Gorokhovsky, Jeffrey L. Anderson
Abstract. Data assimilation (DA), the statistical combination ofcomputer models with measurements, is applied in a variety of scientificfields involving forecasting of dynamical systems, most prominently inatmospheric and ocean sciences. The existence of misreported or unknownobservation times (time error) poses a unique and interesting problem forDA. Mapping observations to incorrect times causes bias in the prior stateand affects assimilation. Algorithms that can improve the performance ofensemble Kalman filter DA in the presence of observing time error aredescribed. Algorithms that can estimate the distribution of time error arealso developed. These algorithms are then combined to produce extensions toensemble Kalman filters that can both estimate and correct for observationtime errors. A low-order dynamical system is used to evaluate theperformance of these methods for a range of magnitudes of observation timeerror. The most successful algorithms must explicitly account for thenonlinearity in the evolution of the prediction model.
摘要数据同化(DA)是计算机模型与测量的统计组合,应用于各种科学领域,包括动力系统的预测,最突出的是大气科学和海洋科学。误报或未知观测时间(时间误差)的存在给DA带来了一个独特而有趣的问题。将观测结果映射到不正确的时间会导致先前状态的偏差,并影响同化。描述了在存在观测时间误差的情况下,可以提高组合卡尔曼滤波器DA性能的算法。还开发了可以估计时间误差分布的算法。然后将这些算法组合在一起,以产生组合卡尔曼滤波器的扩展,卡尔曼滤波器既可以估计观测时间误差,也可以校正观测时间误差。使用低阶动力系统来评估这些方法在观测时间误差范围内的性能。最成功的算法必须明确说明预测模型进化过程中的非线性。
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引用次数: 0
On the interaction of stochastic forcing and regime dynamics 随机强迫与状态动力学的相互作用
IF 2.2 4区 地球科学 Q3 GEOSCIENCES, MULTIDISCIPLINARY Pub Date : 2023-02-07 DOI: 10.5194/npg-30-49-2023
J. Dorrington, T. Palmer
Abstract. Stochastic forcing can, sometimes, stabilise atmospheric regime dynamics, increasing their persistence. This counter-intuitive effect has been observed in geophysical models of varying complexity, and here we investigate the mechanisms underlying stochastic regime dynamics in a conceptual model. We use a six-mode truncation of a barotropic β-plane model, featuring transitions between analogues of zonal and blocked flow conditions, and identify mechanisms similar to those seen previously in work on low-dimensional random maps. Namely, we show that a geometric mechanism, here relating to monotonic instability growth, allows for asymmetric action of symmetric perturbations on regime lifetime and that random scattering can “trap” the flow in more stable regions of phase space. We comment on the implications for understanding more complex atmospheric systems.
摘要随机强迫有时可以稳定大气状态动力学,增加其持久性。这种反直觉效应已经在不同复杂性的地球物理模型中观察到,在这里,我们研究了概念模型中随机状态动力学的机制。我们使用了正压β平面模型的六模截断,该模型具有在类似的纬向和阻塞流动条件之间的转换,并确定了类似于先前在低维随机图上看到的机制。也就是说,我们证明了与单调不稳定增长有关的几何机制,允许对称扰动对状态寿命的不对称作用,并且随机散射可以在相空间的更稳定区域“捕获”流动。我们评论了对理解更复杂的大气系统的影响。
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引用次数: 4
Brief communication: Climate science as a social process – history, climatic determinism, Mertonian norms and post-normality 简要交流:气候科学作为一个社会过程-历史,气候决定论,默顿规范和后常态
IF 2.2 4区 地球科学 Q3 GEOSCIENCES, MULTIDISCIPLINARY Pub Date : 2023-01-31 DOI: 10.5194/npg-30-31-2023
H. von Storch
Abstract. For ages, the topic of climate – in the sense of “usual weather” – has in the western tradition attracted attention as a possible explanatory factor for differences in societies and in human behavior. Climate, and its purported impact on society, is an integrated element in western thinking and perception. In this essay, the history of ideas about the climatic impact on humans and society and the emergence of the ideology of climatic determinism are sketched from the viewpoint of a natural scientist. This ideology favored the perception of westerners being superior to the people in the rest of the world, giving legitimacy to colonialism. In modern times, when natural sciences instituted self-critical processes (repeatability, falsification) and norms (such as the Mertonian norms named CUDOS), the traditional host for climate issues, namely, geography, lost its grip, and physics took over. This “scientification” of climate science led to a more systematic, critical and rigorous approach of building and testing hypotheses and concepts. This gain in methodical rigor, however, went along with the loss of understanding that climate is hardly a key explanatory factor for societal differences and developments. Consequently, large segments of the field tacitly and unknowingly began reviving the abandoned concept of climatic determinism. Climate science finds itself in a “post-normal” condition, which leads to a frequent dominance of political utility over methodical rigor.
摘要多年来,气候这个话题——在“正常天气”的意义上——在西方传统中作为社会差异和人类行为差异的一个可能的解释因素而引起了人们的注意。气候,以及它对社会的影响,是西方思想和观念的一个重要组成部分。本文从一个自然科学家的角度,概述了气候对人类和社会影响的思想历史,以及气候决定论思想的出现。这种意识形态倾向于认为西方人比世界其他地方的人优越,为殖民主义提供了合法性。在现代,当自然科学建立了自我批判的过程(可重复性,可证伪性)和规范(如被称为CUDOS的默顿规范)时,气候问题的传统宿主,即地理学,失去了控制,而物理学取而代之。这种气候科学的“科学化”导致了一种更系统、更批判性和更严格的方法来建立和测试假设和概念。然而,在严谨的方法论上的进步的同时,人们也失去了对气候几乎不是社会差异和发展的关键解释因素的认识。因此,该领域的大部分人在不知情的情况下开始悄悄恢复被抛弃的气候决定论概念。气候科学发现自己处于一种“后常态”状态,这导致政治效用经常占主导地位,而不是系统的严谨性。
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引用次数: 1
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Nonlinear Processes in Geophysics
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