scholarly journals A new dynamical systems perspective on atmospheric predictability: Eastern Mediterranean weather regimes as a case study

2019 ◽  
Vol 5 (6) ◽  
pp. eaau0936 ◽  
Author(s):  
Assaf Hochman ◽  
Pinhas Alpert ◽  
Tzvi Harpaz ◽  
Hadas Saaroni ◽  
Gabriele Messori
Keyword(s):  
Dynamical Systems ◽  
Degrees Of Freedom ◽  
Large Scale ◽  
Climate Model ◽  
Eastern Mediterranean ◽  
Cmip5 Models ◽  
Local Dimension ◽  
Geographical Regions ◽  
Recent Developments ◽  
New Perspective

The atmosphere is a chaotic system displaying recurrent large-scale configurations. Recent developments in dynamical systems theory allow us to describe these configurations in terms of the local dimension—a proxy for the active number of degrees of freedom—and persistence in phase space, which can be interpreted as persistence in time. These properties provide information on the intrinsic predictability of an atmospheric state. Here, this technique is applied to atmospheric configurations in the eastern Mediterranean, grouped into synoptic classifications (SCs). It is shown that local dimension and persistence, derived from reanalysis and CMIP5 models’ daily sea-level pressure fields, can serve as an extremely informative qualitative method for evaluating the predictability of the different SCs. These metrics, combined with the SC transitional probability approach, may be a valuable complement to operational weather forecasts and effective tools for climate model evaluation. This new perspective can be extended to other geographical regions.

scholarly journals Dynamical Properties of the North Atlantic Atmospheric Circulation in the Past 150 Years in CMIP5 Models and the 20CRv2c Reanalysis

2018 ◽  
Vol 31 (15) ◽  
pp. 6097-6111 ◽  
Author(s):  
David Rodrigues ◽  
M. Carmen Alvarez-Castro ◽  
Gabriele Messori ◽  
Pascal Yiou ◽  
Yoann Robin ◽  
...  
Keyword(s):  
Dynamical Systems ◽  
Atmospheric Circulation ◽  
North Atlantic ◽  
Large Scale ◽  
Cmip5 Models ◽  
Historical Period ◽  
Local Dimension ◽  
The North ◽  
The North Atlantic ◽  
Over Time

It is of fundamental importance to evaluate the ability of climate models to capture the large-scale atmospheric circulation patterns and, in the context of a rapidly increasing greenhouse forcing, the robustness of the changes simulated in these patterns over time. Here we approach this problem from an innovative point of view based on dynamical systems theory. We characterize the atmospheric circulation over the North Atlantic in the CMIP5 historical simulations (1851–2000) in terms of two instantaneous metrics: local dimension of the attractor and stability of phase-space trajectories. We then use these metrics to compare the models to the Twentieth Century Reanalysis version 2c (20CRv2c) over the same historical period. The comparison suggests that (i) most models capture to some degree the median attractor properties, and models with finer grids generally perform better; (ii) in most models the extremes in the dynamical systems metrics match large-scale patterns similar to those found in the reanalysis; (iii) changes in the attractor properties observed for the ensemble-mean 20CRv2c are artifacts resulting from inhomogeneities in the standard deviation of the ensemble over time; and (iv) the long-term trends in local dimension observed among the 56 members of the 20CR ensemble have the same sign as those observed in the CMIP5 multimodel mean, although the multimodel trend is much weaker.

scholarly journals Improvements of organic aerosol representations and their effects in large-scale atmospheric models

2012 ◽  
Vol 12 (18) ◽  
pp. 8687-8709 ◽  
Author(s):  
H. Tost ◽  
K. J. Pringle
Keyword(s):  
Oxidation State ◽  
Large Scale ◽  
Climate Model ◽  
Field Measurements ◽  
Organic Aerosol ◽  
Climate Impact ◽  
Scale Modelling ◽  
Recent Developments ◽  
Fine Mode ◽  
New Formulation

Abstract. Organics dominate the composition of the atmospheric aerosol, especially in the fine mode, influencing some of its characteristics such as the hygroscopicity, which is of climatic relevance for the Earth system. This study targets an improvement in the description of organic aerosols suitable for large-scale modelling, making use of recent developments based on laboratory and field measurements. In addition to the organic mass and particle number distribution, the proposed method keeps track of the oxidation state of the aerosol based on the OH exposure time, describing some of its chemical characteristics. This study presents the application of the method in a global chemistry climate model, investigates the sensitivity to process formulations and emission assignments, provides a comparison with observations and analyses the climate impact. Even though the organic aerosol mass distribution is hardly affected by the new formulation, it shows impacts (regionally of the order of 10 % to 20 %) on parameters directly influencing climate via the direct and indirect aerosol effects. Furthermore, the global distribution of the organic O:C ratio is analysed in detail, leading to different regimes in the oxidation state: low O:C ratios over the tropical continents due to small OH concentrations caused by OH depletion in chemical reactions, and enhanced oxidation states over the tropical oceans based on less OH scavengers and at high altitudes due to longer atmospheric residence time. Due to the relation between O:C ratio and the aerosol hygroscopicity the ageing results in a more physically and chemically consistent description of aerosol water uptake by the organic aerosol. In comparison with observations reasonable agreement for the O:C ratio within the limits of a global model of the simulations is achieved.

scholarly journals Saharan Heat Low Biases in CMIP5 Models

2017 ◽  
Vol 30 (8) ◽  
pp. 2867-2884 ◽  
Author(s):  
Ross D. Dixon ◽  
Anne Sophie Daloz ◽  
Daniel J. Vimont ◽  
Michela Biasutti
Keyword(s):  
Large Scale ◽  
Climate Models ◽  
Climate Model ◽  
Global Climate ◽  
West African Monsoon ◽  
West African ◽  
Global Climate Models ◽  
Cmip5 Models ◽  
African Climate ◽  
Heat Low

Representing the West African monsoon (WAM) is a major challenge in climate modeling because of the complex interaction between local and large-scale mechanisms. This study focuses on the representation of a key aspect of West African climate, namely the Saharan heat low (SHL), in 22 global climate models from phase 5 of the Coupled Model Intercomparison Project (CMIP5) multimodel dataset. Comparison of the CMIP5 simulations with reanalyses shows large biases in the strength and location of the mean SHL. CMIP5 models tend to develop weaker climatological heat lows than the reanalyses and place them too far southwest. Models that place the climatological heat low farther to the north produce more mean precipitation across the Sahel, while models that place the heat low farther to the east produce stronger African easterly wave (AEW) activity. These mean-state biases are seen in model ensembles with both coupled and fixed sea surface temperatures (SSTs). The importance of SSTs on West African climate variability is well documented, but this research suggests SSTs are secondary to atmospheric biases for understanding the climatological SHL bias. SHL biases are correlated across the models to local radiative terms, large-scale tropical precipitation, and large-scale pressure and wind across the Atlantic, suggesting that local mechanisms that control the SHL may be connected to climate model biases at a much larger scale.

A Method for Solving Large-Scale Multiloop Constrained Dynamical Systems Using Structural Decomposition

2016 ◽  
Vol 12 (3) ◽  
Author(s):  
Tao Xiong ◽  
Jianwan Ding ◽  
Yizhong Wu ◽  
Liping Chen ◽  
Wenjie Hou
Keyword(s):  
Dynamical Systems ◽  
Degrees Of Freedom ◽  
Large Scale ◽  
The State ◽  
State Variables ◽  
Structural Decomposition ◽  
Multiple Degrees Of Freedom ◽  
Constraint Equations ◽  
Constrained Dynamical Systems ◽  
Algebraic Constraint

A structural decomposition method based on symbol operation for solving differential algebraic equations (DAEs) is developed. Constrained dynamical systems are represented in terms of DAEs. State-space methods are universal for solving DAEs in general forms, but for complex systems with multiple degrees-of-freedom, these methods will become difficult and time consuming because they involve detecting Jacobian singularities and reselecting the state variables. Therefore, we adopted a strategy of dividing and conquering. A large-scale system with multiple degrees-of-freedom can be divided into several subsystems based on the topology. Next, the problem of selecting all of the state variables from the whole system can be transformed into selecting one or several from each subsystem successively. At the same time, Jacobian singularities can also be easily detected in each subsystem. To decompose the original dynamical system completely, as the algebraic constraint equations are underdetermined, we proposed a principle of minimum variable reference degree to achieve the bipartite matching. Subsequently, the subsystems are determined by aggregating the strongly connected components in the algebraic constraint equations. After that determination, the free variables remain; therefore, a merging algorithm is proposed to allocate these variables into each subsystem optimally. Several examples are given to show that the proposed method is not only easy to implement but also efficient.

scholarly journals Classifications of Winter Euro-Atlantic Circulation Patterns: An Intercomparison of Five Atmospheric Reanalyses

2017 ◽  
Vol 30 (19) ◽  
pp. 7847-7861 ◽  
Author(s):  
Jan Stryhal ◽  
Radan Huth
Keyword(s):  
Twentieth Century ◽  
Mediterranean Region ◽  
Large Scale ◽  
Climate Models ◽  
Eastern Mediterranean ◽  
Eastern Mediterranean Region ◽  
Synoptic Climatology ◽  
Cmip5 Models ◽  
Circulation Patterns ◽  
Twentieth Century Reanalysis

Abstract Atmospheric reanalyses have been widely used to study large-scale atmospheric circulation and its links to local weather and to validate climate models. Only little effort has so far been made to compare reanalyses over the Euro-Atlantic domain, with the exception of a few studies analyzing North Atlantic cyclones. In particular, studies utilizing automated classifications of circulation patterns—one of the most popular methods in synoptic climatology—have paid little or no attention to the issue of reanalysis evaluation. Here, five reanalyses [ERA-40; NCEP-1; JRA-55; Twentieth Century Reanalysis, version 2 (20CRv2); and ECMWF twentieth-century reanalysis (ERA-20C)] are compared as to the frequency of occurrence of circulation types (CTs) over eight European domains in winters 1961–2000. Eight different classifications are used in parallel with the intention to eliminate possible artifacts of individual classification methods. This also helps document how substantial effect a choice of method can have if one quantifies differences between reanalyses. In general, ERA-40, NCEP-1, and JRA-55 exhibit a fairly small portion of days (under 8%) classified to different CTs if pairs of reanalyses are compared, with two exceptions: over Iceland, NCEP-1 shows disproportionately high frequencies of CTs with cyclones shifted south- and eastward; over the eastern Mediterranean region, ERA-40 and NCEP-1 disagree on classification of about 22% of days. The 20CRv2 is significantly different from other reanalyses over all domains and has a clearly suppressed frequency of zonal CTs. Finally, validation of 32 CMIP5 models over the eastern Mediterranean region reveals that using different reanalyses can considerably alter errors in the CT frequency of models and their rank.

scholarly journals Future changes in the relationship of precipitation intensity in Eastern Mediterranean with large scale circulation

2010 ◽  
Vol 23 ◽  
pp. 31-36 ◽  
Author(s):  
M. Hatzaki ◽  
H. A. Flocas ◽  
C. Oikonomou ◽  
C. Giannakopoulos
Keyword(s):  
Large Scale ◽  
Climate Model ◽  
Eastern Mediterranean ◽  
Regional Climate ◽  
Circulation Model ◽  
Global Circulation Model ◽  
Intensity Index ◽  
Teleconnection Patterns ◽  
European Area ◽  
The Future

Abstract. The objective of this study is to investigate the linkage of large-scale upper air circulation over the greater European area with intense precipitation events over Eastern Mediterranean and then to estimate potential changes in the atmospheric patterns in the future, under global warming conditions. For this purpose, results from the regional climate model HadRM3P and Global Circulation Model HadAM3P have been used for the present period 1960–1990 (control run) and the future period 2070–2100 based on the B2a IPCC emission scenario. For the identification of the precipitation extremes the Simple Daily Intensity Index (SDII) was employed. Our analysis has shown a notable relation of extreme events with the East Atlantic and Scandinavia teleconnection patterns, as well as the Eastern Mediterranean Pattern (EMP) during the wet period. In the future, similar patterns are found, with different magnitude and position, following the projected changes in atmospheric circulation over Europe.

scholarly journals Warm Season Dry Spells in the Central and Eastern United States: Diverging Skill in Climate Model Representation

2016 ◽  
Vol 29 (15) ◽  
pp. 5617-5624 ◽  
Author(s):  
Siyu Zhao ◽  
Yi Deng ◽  
Robert X. Black
Keyword(s):  
United States ◽  
Large Scale ◽  
Climate Model ◽  
Warm Season ◽  
Hierarchical Cluster ◽  
Model Representation ◽  
Cmip5 Models ◽  
Eastern United States ◽  
Dry Spells ◽  
Dry Spell

Abstract Warm season dry spells over the central and eastern United States are classified into three canonical types via a hierarchical cluster analysis for the period 1950–2005. Four CMIP5 models exhibit diverging skill in representing the observed behavior, ranging from southern Great Plains dry spells that are reasonably simulated by all four models to southeastern U.S. dry spells that are only accurately captured by one model. A model’s skill in representing a particular dry spell cluster is positively correlated with the model’s ability to simulate the large-scale meteorological patterns (LMPs) accompanying the dry spell. The interannual variability and overall observed decreasing trend in dry spell days are represented with varying degrees of accuracy by the four models. The results 1) highlight existing shortcomings in the climate model representation of regional dry spells and 2) illustrate the importance of properly simulating the observed spectrum of LMPs in minimizing these shortcomings.

Dynamics of Large Scale Mechanical Models Using Multilevel Substructuring

2006 ◽  
Vol 2 (1) ◽  
pp. 40-51 ◽  
Author(s):  
C. Papalukopoulos ◽  
S. Natsiavas
Keyword(s):  
Dynamical Systems ◽  
Degrees Of Freedom ◽  
Large Scale ◽  
Equations Of Motion ◽  
Numerical Results ◽  
Ground Vehicles ◽  
Response Characteristics ◽  
Sparsity Pattern ◽  
Mechanical Models ◽  
Set Up

An appropriate substructuring methodology is applied in order to study the dynamic response of very large scale mechanical systems. The emphasis is put on enabling a systematic study of dynamical systems with nonlinear characteristics, but the method is equally applicable to systems possessing linear properties. The accuracy and effectiveness of the methodology are illustrated by numerical results obtained for example vehicle models, having a total number of degrees of freedom lying in the order of a million or even bigger. First, the equations of motion of each component are set up by applying the finite element method. The order of the resulting models is so high that the classical substructuring methodologies become numerically ineffective or practically impossible to apply. However, the method developed overcomes these difficulties by imposing a further, multilevel substructuring of each component, based on the sparsity pattern of the stiffness matrix. In this way, the number of the equations of motion of the complete system is substantially reduced. Consequently, the numerical results presented demonstrate that besides the direct computational savings, this reduction in the dimensions enables the application of numerical codes, which capture response characteristics of dynamical systems sufficiently accurate up to a prespecified level of forcing frequencies. The study concludes by investigating biodynamic response of passenger-seat subsystem models coupled with complex mechanical models of ground vehicles resulting from deterministic or random road excitation.

scholarly journals Improvements of organic aerosol representations and their effects in large-scale atmospheric models

2012 ◽  
Vol 12 (4) ◽  
pp. 10331-10379
Author(s):  
H. Tost ◽  
K. J. Pringle
Keyword(s):  
Oxidation State ◽  
Large Scale ◽  
Climate Model ◽  
Field Measurements ◽  
Organic Aerosol ◽  
Climate Impact ◽  
Scale Modelling ◽  
Recent Developments ◽  
Fine Mode ◽  
New Formulation

Abstract. Organics dominate the composition of the atmospheric aerosol, especially in the fine mode, influencing some of its characteristics such as the hygroscopicity, which is of climatic relevance for the Earth system. This study targets an improvement in the description of organic aerosols suitable for large-scale modelling, making use of recent developments based on laboratory and field measurements. In addition to the organic mass and particle number distribution, the proposed method keeps track of the oxidation state of the aerosol based on the OH exposure time, describing some of its chemical characteristics. This study presents the application of the method in a global chemistry climate model, investigates the sensitivity to process formulations and emission assignments, provides a comparison with observations and analyses the climate impact. Even though the organic aerosol mass distribution is hardly affected by the new formulation, it shows impacts (regionally of the order of 10% to 20%) on parameters directly influencing climate via the direct and indirect aerosol effects. Furthermore, the global distribution of the organic O:C ratio is analysed in detail, leading to different regimes in the oxidation state: low O:C ratios over the tropical continents due to small OH concentrations caused by OH depletion in chemical reactions, and enhanced oxidation states over the tropical oceans based on the OH abundance and at high altitudes due to longer atmospheric residence time. Due to the relation between O:C ratio and the aerosol hygroscopicity the ageing results in a more accurate description of aerosol water uptake by the organic aerosol. In comparison with observations reasonable agreement within the limits of a global model of the simulations is achieved.

The Role of Zonally Averaged Climate Change in Contributing to Intermodel Spread in CMIP5 Predicted Local Precipitation Changes

2020 ◽  
Vol 33 (3) ◽  
pp. 1141-1154 ◽  
Author(s):  
Chaim I. Garfinkel ◽  
Ori Adam ◽  
Efrat Morin ◽  
Yehoudah Enzel ◽  
Eilat Elbaum ◽  
...  
Keyword(s):  
Surface Temperature ◽  
Large Scale ◽  
Eastern Mediterranean ◽  
The United States ◽  
Hadley Cell ◽  
Cmip5 Models ◽  
Upper Troposphere ◽  
The Mediterranean ◽  
Precipitation Changes ◽  
Tropical Upper Troposphere

AbstractWhile CMIP5 models robustly project drying of the subtropics and more precipitation in the tropics and subpolar latitudes by the end of the century, the magnitude of these changes in precipitation varies widely across models: for example, some models simulate no drying in the eastern Mediterranean while others simulate more than a 50% reduction in precipitation relative to the model-simulated present-day value. Furthermore, the factors leading to changes in local subtropical precipitation remain unclear. The importance of zonal-mean changes in atmospheric structure for local precipitation changes is explored in 42 CMIP5 models. It is found that up to half of the local intermodel spread over the Mediterranean, northern Mexico, East Asia, southern Africa, southern Australia, and southern South America is related to the intermodel spread in large-scale processes such as the magnitude of globally averaged surface temperature increases, Hadley cell widening, polar amplification, stabilization of the tropical upper troposphere, or changes in the polar stratosphere. Globally averaged surface temperature increases account for intermodel spread in land subtropical drying in the Southern Hemisphere but are not important for land drying adjacent to the Mediterranean. The factors associated with drying over the eastern Mediterranean and western Mediterranean differ, with stabilization of the tropical upper troposphere being a crucial factor for the former only. Differences in precipitation between the western and eastern Mediterranean are also evident on interannual time scales. In contrast, the global factors examined here are unimportant over most of the United States, and more generally over the interior of continents. Much of the rest of the spread can be explained by variations in local relative humidity, a proxy also for zonally asymmetric circulation and thermodynamic changes.

Sign in / Sign up

Export Citation Format

Share Document