Dynamical Evolution of Barred Galaxies     

E. Athanassoula 《Celestial Mechanics and Dynamical Astronomy》2005,91(1-2):9-31

Angular momentum redistribution within barred galaxies drives their dynamical evolution. Angular momentum is emitted mainly by near-resonant material in the bar region and absorbed by resonant material mainly in the outer disc and in the halo. This exchange determines the strength of the bar, the decrease of its pattern speed, as well as its morphology. If the galaxy has also a gaseous component and/or a companion or satellite, then these also take part in the angular momentum exchange. During the evolution a bar structure forms in the inner parts of the halo as well. This bar is shorter and fatter than the disc bar and stays so all through the simulation, although its length grows considerably with time. Viewed edge-on, the bar in the disc component acquires a boxy or peanut shape. I describe the families of periodic orbits that explain such structures and review the observations showing that boxy/peanut ‘bulges’ are in fact just bars seen edge-on.  相似文献   

A numerical solution of the dynamical instability of a thin accretion torus     

Liu Ren-jie  Wang De-yu 《Chinese Astronomy and Astrophysics》1995,19(4):507-512

We consider the non-axisymmetric, dynamical instability of a thin accretion torus with a non-zero shift of corotation radius. By numerical method we evaluated the wave number dependence of the linear rate of growth of instability and the co-rotation shift. The rate of growth is only slightly affected by the non-zero co-rotation shift, while the dispersion relation in the case of a shift is the same as that of the linear KdV equation. This shows that the “planet-like” solution found in numerical simulations of thin tori is very probably analogous to the soliton solution of the KdV equation.  相似文献   

The general solution of the HENON–HEILES problem     

K.?E.?PapadakisEmail author  C.?L.?Goudas  G.?A.?Katsiaris 《Astrophysics and Space Science》2005,295(3):375-396

The general solution of the Henon–Heiles system is approximated inside a domain of the (x, C) of initial conditions (C is the energy constant). The method applied is that described by Poincaré as ‘the only “crack” permitting penetration into the non-integrable problems’ and involves calculation of a dense set of families of periodic solutions that covers the solution space of the problem. In the case of the Henon–Heiles potential we calculated the families of periodic solutions that re-enter after 1–108 oscillations. The density of the set of such families is defined by a pre-assigned parameter ε (Poincaré parameter), which ascertains that at least one periodic solution is computed and available within a distance ε from any point of the domain (x, C) for which the approximate general solution computed. The approximate general solution presented here corresponds to ε = 0.07. The same solution is further improved by “zooming” into four square sub-domain of (x, C), i.e. by computing sufficient number of families that reduce the density parameter to ε = 0.003. Further zooming to reduce the density parameter, say to ε = 10⁻⁶, or even smaller, although easily performable in both areas occupied by stable as well as unstable solutions, was found unnecessary. The stability of all members of each and all families computed was calculated and presented in this paper for both the large solution domain and for the sub-domains. The correspondence between areas of the approximate general solution occupied by stable periodic solutions and Poincaré sections with well-aligned section points and also correspondence between areas occupied by unstable solutions and Poincaré sections with randomly scattered section points is shown by calculating such sections. All calculations were performed using the Runge-Kutta (R-K) 8th order direct integration method and the large output received, consisting of many thousands of families is saved as “Atlas of the General Solution of the Henon–Heiles Problem,” including their stability and is available at request. It is concluded that approximation of the general solution of this system is straightforward and that the chaotic character of its Poincaré sections imposes no limitations or difficulties.  相似文献   

三维社区建模与分析的共形几何代数方法     

罗文  袁林旺  胡勇  易琳  闾国年 《地理与地理信息科学》2012,28(3):20-23,53

利用共形几何代数的多维统一表达与分析优势,研究了集成多源数据的三维社区统一建模与分析方法。构建了基于多重向量存储结构的社区场景整体建模流程,实现了CityGML、DXF等多源数据的导入与集成,并设计了基于共形几何代数的对象运动表达与插值方法。以德国Waldbruecke村为例的验证结果显示,基于共形几何代数的三维社区建模可以较好地表达复杂社区对象,并可以有效支撑几何度量、动态对象跟踪、运动轨迹重建等功能实现。  相似文献   

Circulation Around Luzon Strait in September as Inferred from CTD,Argos and Argo Measurements and a Generalized Topography-Following Ocean Model     

《大气与海洋》2012,50(4):40-58

The hydrography, wind, Argos and Argo measurements in the areas surrounding Luzon Strait were collected. Based on the hydrographic data obtained during September 1994, the improved Princeton Ocean Model using a generalized topography-following coordinate system together with a modified inverse method was applied to study the circulation in September. Observations and the diagnostic simulation produce a consistent circulation pattern, and the main dynamical features can be summarized as follows. (1) The Kuroshio has two branches with the main Kuroshio existing above 800 m depth and the western part existing above 400 m depth. The western branch of the Kuroshio leaves the main current near 20.5°N, then flows northwestward through Luzon Strait and finally flows out of the northern boundary southwest of Taiwan, consistent with the trajectory of Argos drifters. (2) The non-linear term is important and cannot be neglected in the momentum equations in the northern part of Luzon Strait under the baroclinicity field. Using non-linear dynamics, the westward intrusion of the Kuroshio into the northern part of Luzon Strait is more curved than when using linear dynamics. However, the non-linear term is smaller and so negligible around Luzon Strait under the homogeneous density field. (3) In the area from 117°E to 119°E and from 20.2°N to 21.7°N, an anticyclonic eddy appears east of Dongsha Islands. (4) At depths above 400 m, the circulation is mainly dominated by the basin-scale cyclonic gyre. (5) In the computational domain west of 121°E, the circulation below 800 m is mainly dominated by the basin-scale anticyclonic gyre. (6) The South China Sea water flows eastward across Luzon Strait in the middle layers, then turns cyclonically, finally flowing northward into the region east of Taiwan Island, which is qualitatively in agreement with the trajectories of Argo floats at about 1000 m depth in the area east of 121°E.

RÉSUMÉ?[Traduit par la rédaction] Nous avons rassemblé l'hydrographie, le vent, les Argo et les mesures Argo dans les régions avoisinant le détroit de Luçon. Sur la base des données hydrographiques relevées durant le mois de septembre 1994, nous avons appliqué le modèle océanique amélioré de Princeton utilisant un système de coordonnées « suivant le terrain » généralisé de pair avec une méthode inverse modifiée pour étudier la circulation en septembre. Les observations et la simulation diagnostique produisent une configuration de circulation cohérente dont on peut résumer comme suit les principales caractéristiques dynamiques. (1) Le Kuroshio possède deux branches : le Kuroshio principal existant au-dessus d'une profondeur de 800 m et la partie ouest existant au-dessus d'une profondeur de 400 m. La branche ouest du Kuroshio quitte le courant principal aux environs de 20,5°N et se dirige vers le nord-ouest à travers le détroit de Luçon pour finalement franchir la limite nord du détroit au sud-ouest de Taïwan, ce qui correspond à la trajectoire des bouées dérivantes Argos. (2) Le terme non linéaire dans les équations est important et ne peut pas être considéré négligeable de quantité de mouvement dans la partie nord du détroit de Luçon dans le champ de baroclinité. Lorsqu'on utilise la dynamique non linéaire, l'intrusion vers l'ouest du Kuroshio dans la partie nord du détroit de Luçon est plus incurvée que lorsqu'on utilise la dynamique linéaire. Cependant, le terme non linéaire est plus petit et donc négligeable autour du détroit de Luçon dans le champ de densité homogène. (3) Dans la région allant de 117°E à 119°E et de 20,2°N à 21,7°N, un remous anticyclonique apparaît à l'est des îles Dongsha. (4) Aux profondeurs inférieures à 400 m, la circulation est principalement dominée par le gyre cyclonique à l’échelle du bassin. (5) Dans le domaine de calcul à l'ouest de 121°E, la circulation sous 800 m est principalement dominée par le gyre anticyclonique à l’échelle du bassin. (6) Les eaux de la mer de Chine méridionale s’écoulent vers l'est à travers le détroit de Luçon dans les couches intermédiaires, puis tournent de façon cyclonique pour finalement s’écouler vers le nord dans la région à l'est de l’île Taïwan, ce qui, qualitativement, s'accorde avec la trajectoire des flotteurs Argo à environ 1000 m de profondeur dans la région à l'est de 121°E.  相似文献   

基于统计降尺度模型的江淮流域极端气候的模拟与预估   总被引：4，自引：0，他引：4  

陈威霖  江志红  黄强 《南京气象学院学报》2012,(5):578-590

利用江淮流域29个代表站点1961--2000年逐日最高温度、最低温度和逐日降水资料,以及NCEP逐日大尺度环流场资料,引入基于多元线性回归与随机天气发生器相结合的统计降尺度模型SDSM（statistical downscalingmodel）,通过对每个站点建模,确立SDSM参数,并将该模型应用于SRESA2排放情景下HadCM3和cGcM3模式,得到了江淮流域各代表台站21世纪的逐日最高、最低温度和降水序列以及热浪、霜冻、强降水等极端气候指数。结果表明,当前气候下,统计降尺度方法模拟的极端温度指数与观测值有很好的一致性,能有效纠正耦合模式的“冷偏差”,如SDSM对江淮平均的冬季最高、最低温度的模拟偏差较CGCM3模式分别减少3℃和4．5℃。对于极端降水则能显著纠正耦合模式模拟的降水强度偏低的问题,如CGCM3对江淮流域夏季降水强度的模拟偏差为-60．6％,但降尺度后SDSM—CGCM3的偏差仅为-6％,说明降尺度模型SDSM的确有“增加值”的作用。21世纪末期在未来SRESA2情景下,对于极端温度,无论Had．CM3还是CGCM3模式驱动统计模型,江淮流域所有代表台站,各个季节的最高、最低温度都显著增加,且以夏季最为显著,增幅在2—4℃;与之相应霜冻天数将大幅减少,热浪天数大幅增多,各站点冬季霜冻天数减少幅度为5—25d,夏季热浪天数增加幅度为4～14d;对于极端降水指数,在两个不同耦合模式HadCM3和CGCM3驱动下的变化尤其是变化幅度的一致性比温度差,但大部分站点各个季节极端强降水事件将增多,强度增强,SDSM—HadCM3和SDSM-CGCM3预估的夏季极端降水贡献率将分别增加26％和27％。  相似文献   

异常气温作用于水稻一维能量模型的数值分析     

刘春  张春辉  郭萨萨 《气象研究与应用》2012,33(2):49-54

应用动力学方程建立四川内江市水稻的生长模型,通过FORCAL和MATLAB对方程参数拟合,并进行数值分析和定性分析,为水稻产量预报和气温对水稻生物量的影响评估提供科学依据。在传统的一维能量模型基础上,将水稻对外界能量的摄取能力与水稻生长季中的气温变化规律联系起来,得到水稻的生长曲线x（t）,并通过相平面轨迹得到x—T曲线,定性分析水稻的临界气温和最快生长率出现时间。通过低温对水稻分蘖期和高温对生殖生长期影响的比较,得出如下结论：水稻后期受高温影响比前期受低温影响严重。  相似文献   

STUDY OF THE EFFECTS OF REDUCING SYSTEMATIC ERRORS ON MONTHLY REGIONAL CLIMATE DYNAMICAL FORECAST     

曾新民  席朝笠 《热带气象学报(英文版)》2009,15(1):102-105

A nested-model system is constructed by embedding the regional climate model RegCM3 into a general circulation model for monthly-scale regional climate forecast over East China. The systematic errors are formulated for the region on the basis of 10-yr (1991-2000) results of the nested-model system, and of the datasets of the Climate Prediction Center (CPC) Merged Analysis of Precipitation (CMAP) and the temperature analysis of the National Meteorological Center (NMC), U.S.A., which are then used for correcting the original forecast by the system for the period 2001-2005. After the assessment of the original and corrected forecasts for monthly precipitation and surface air temperature, it is found that the corrected forecast is apparently better than the original, suggesting that the approach can be applied for improving monthly-scale regional climate dynamical forecast.  相似文献   

区域风能资源评价分析的动力降尺度研究   总被引：7，自引：0，他引：7  

李艳  汤剑平  王元  江志红  储惠芸 《气候与环境研究》2009,14(2):192-200

不同于以往的统计风能评估方法,本研究将动力降尺度方法应用到江苏省的风能评价分析中。利用NCEP/NCAR再分析资料与江苏省65个地面气象观测站1971～2000年的观测资料,建立了动力降尺度区域气候模式MM5V3的初始场和边界条件,用较高分辨率（水平分辨率为5 km）评估了江苏省60 m高度的风能分布,分析了动力降尺度方法在区域风能资源评估中的有效应用。结果表明,江苏省风能资源由东部沿海向西部内陆递减,以西连岛为代表的东部沿海风能资源最丰富,其次为长江三角洲地区,太湖、洪泽湖及高邮湖地区的风能资源也比较丰富,徐州市与南京市的风能资源最贫乏。分析表明,动力降尺度方法能够用较高分辨率模拟局地环流和地面风的主要分布特征,可以作为区域风能资源评价分析的有效手段。  相似文献   

最优子集回归方法在季节气候预测中的应用   总被引：7，自引：1，他引：6  

柯宗建  张培群  董文杰 《大气科学》2009,33(5):994-1002

利用DEMETER计划多个模式的模拟资料研究1959～2001年多模式集合预报的季节降水在中国区域的表现, 并结合最优子集回归(OSR)方法对中国区域的季节降水进行降尺度预报, 比较其与多模式集合预报的技巧。研究表明: 多个单模式在中国区域对季节降水的模拟性能普遍较差, 多元线性回归(MLR)集合的预报技巧不如集合平均(EM)。利用OSR方法进行降尺度预报可以极大改善中国区域季节降水的预报技巧。夏季, 降水距平相关系数(ACC)在长江以南、西藏以及内蒙古中部等地区提高很显著, ACC在中国区域的平均达到0.29, 明显高于多模式集合平均与多元线性回归集合。冬季, OSR方法可以改善多模式集合在中国北方地区较低的预报技巧。概率Brier技巧评分(BSS)也表明了OSR方法对季节降水预报的改善。需要说明的是, 虽然OSR方法在中国区域能明显提高季节降水的预报技巧, 但是其选取的预报因子与中国区域季节降水的物理机制问题仍有待于进一步的研究。  相似文献