长江下游旱涝与夏半年欧亚环流30～60天振荡的年际变化   总被引：6，自引：0，他引：6  

杨秋明 《气象学报》2001,59(3):318-326

对 2 5a(1 971～ 1 995年 )逐候东半球热带外 50 0 h Pa高度距平场进行小波分析和旋转主成分分析 ,研究了 30～ 60 d低频振荡的时空变化及其与长江下游夏季旱涝和暴雨频数年际变化的关系。结果表明 :6～ 1 0月欧亚型 (EU)低频振荡强度与长江下游暴雨频数成显著负相关 ,同时 ,提出了能揭示变量间非线性关系的对比函数分析 (CFA)方法 ,发现当 5～ 8月西太平洋型 (WP)低频流型偏强时 ,长江下游暴雨频数增加 ,容易发生洪涝 ;反之 ,无明显影响。仅当前期 3～ 5月南亚大陆型偏强时长江下游降水量偏少 ,而 3～ 5月南亚大陆型偏弱时暴雨频数明显增加。因此 ,长江下游旱涝与低频流型异常之间同时存在线性和非线性相关。  相似文献   

Dynamic analysis of stacked rigid blocks   总被引：1，自引：0，他引：1  

Pol D. Spanos  Panayiotis C. Roussis  Nikolaos P. A. Politis 《Soil Dynamics and Earthquake Engineering》2001,21(7):472

The dynamic behavior of a structural model of two stacked rigid blocks subjected to ground excitation is examined. Assuming no sliding, the rocking response of the system standing free on a rigid foundation is investigated. The derivation of the equations of motion accounts for the consecutive transition from one pattern of motion to another, each being governed by a set of highly nonlinear differential equations. The system behavior is described in terms of four possible patterns of response and impact between either the two blocks or the base block and the ground. The equations governing the rocking response of the system to horizontal and vertical ground accelerations are derived for each pattern, and an impact model is developed by conservation of angular momentum considerations. Numerical results are obtained by developing an ad hoc computational scheme that is capable of determining the response of the system under an arbitrary base excitation. This feature is demonstrated by using accelerograms from the Northridge, CA, 1994, earthquake. It is hoped that the two-blocks model used herein can facilitate the development of more sophisticated multi-block structural models.  相似文献   

科氏力作用下涡旋运动的等值线动力学   总被引：1，自引：1，他引：1       下载免费PDF全文

罗哲贤 《气象学报》1993,51(4):394-404

本文提出了在科氏力作用下,单圈常值涡旋运动等值线动力学的计算公式。用这些公式实施了四组计算,结果与以往动力学分析和数值试验的结论定性一致,数值也较为合理。  相似文献   

偶极子型热源和地形共同强迫下局域流型的演变特征   总被引：1，自引：0，他引：1  

罗哲贤  马镜娴  谢金南 《气象学报》2000,58(3):354-361

用带有热源强迫和地形强迫的准地转正压模式,实施了6组时间积分为72个模式日的数值积分。结果指出：不同的初始状态,会产生不同的渐近行为,包括准平衡态、阻尼振荡和非阻尼振荡,显示出明显的非线性特征。热源强迫场空间结构的复杂程度,对系统时间演变特征也有重要影响。  相似文献   

线性化与形式分析丢失的世界     

欧阳首承 《气象科学》2000,21(3):354-359

本文以罗斯贝方程和爱因斯坦的引力波方程为例,讨论线性化和形式分析构成的物理实在性的失落,及相应“长波”和“引力波”理论存在的问题。  相似文献   

粘性力在地形变动力学模型演化过程中的作用          下载免费PDF全文

张永志 《地震工程学报》1994,16(4):76-80,84

本文分别利用Ｌｙａｐｕｎｏｖ指数方法和特征值方法，对摸拟地震过程的线性粘弹性动力学模型的稳定性进行了分析，并讨论了粘性力在地形变动力学系统演化过程中的作用，采用Ｒｕｎｇｅ－Ｋｕｔｔａ格式的Ｍｅｒｓｏｎ修改方法模拟了在不同粘性系数时线性和非线性动力学系统的演化过程，得出了一些有意义的结论和认识。  相似文献   

Monthly variation of some parameters about internal solitary waves in the South China sea     

《Deep Sea Research Part I: Oceanographic Research Papers》2014

In this paper, by non-dimensional analysis, it is found that finite-depth theory is more appropriate to the study of internal solitary waves (ISWs) in the South China Sea (SCS) than shallow-water theory. The 1-degree grid data of monthly mean temperature and salinity data at standard levels in the SCS are used to solve the linearized vertical eigenvalue problem. The nonlinear parameter and the wave phase speed are computed, then the nonlinear phase speed and the characteristic half-width of ISWs are calculated respectively by two different theories to investigate the difference between these two parameters in the SCS. The nonlinearity is the strongest near the continental slope of the SCS or islands where the bottom topography changes sharply, it is stronger in summer than that in winter; it increases (decreases) as pycnocline depth deepens (shallows), stratification strengthens (weakens) and pycnocline thickness thins (thickens). The nonlinear wave phase speed and the characteristic half-width are the largest in deep sea area, they then reduce peripherally in shallower water. The nonlinear wave phase speed in the SCS changes slightly with time, but the characteristic half-width changes somewhat larger with time. In most of the SCS basin, the nonlinear wave phase speed derived from shallow-water theory is very close to that derived from finite-depth theory, but the characteristic half-width derived from shallow-water theory is about 0.2–0.6 times larger than that derived from finite-depth theory. The ISW induced horizontal current velocity derived from shallow-water theory is larger than that derived from finite-depth theory. Some observed and numerical modeled ISW characteristic half-widths are compared with those derived from shallow-water and finite-depth theories, respectively. It is shown that, the characteristic half-widths derived from finite-depth theory agree better with observational and numerical modeled results than those derived from shallow-water theory in most cases, finite-depth theory is more applicable to the estimation of ISW characteristic half-widths in the northern SCS. It is also suggested that, to derive the precise ISW parameters in further study, the physical non-dimensional ratios which are related with ISW characteristic half-width, amplitude, thermocline and water depths should be calculated, so that an appropriate theory can be chosen for estimation.  相似文献   

Parameterisation and transformation of wave asymmetries over a low-crested breakwater   总被引：1，自引：0，他引：1  

Zhong Peng  Qingping Zou  Dominic Reeve  Baoxing Wang 《Coastal Engineering》2009,56(11-12):1123-1132

This paper presents the results of an investigation of the transformation of wave skewness and asymmetry as waves propagate obliquely over low-crested breakwaters, (LCBs), based on an analysis of measurements collected in the DELOS project. Considering the effect of the local Ursell number on wave asymmetries, a set of practical empirical formulae were established using least squares regression for both smooth and rubble mound LCBs. Predictions are in good agreement with measurements. Wave skewness on both sides of LCBs is linearly correlated for rubble mound LCBs but weakly correlated for smooth LCBs. While wave asymmetry on both sides of LCBs has a weakly quadratic correlation. The effect of the relative freeboard on the relationships of wave asymmetries between both sides is significant for rubble mound LCBs, but the same does not hold for smooth LCBs. With the presence of LCBs, wave skewness retains a positive sign on both sides but asymmetry changes from negative on the incident side to positive on the transmission side. Bispectral analysis shows that positive skewness and negative asymmetry arises from self–self and sum interactions but positive asymmetry is due to difference interactions between frequencies. The findings provide improved understanding of changes in wave skewness and asymmetry in the vicinity of structures, which may help mitigate scour and improve the stability of breakwaters.  相似文献   

东亚中纬冬季雪盖异常对初夏环流的影响          下载免费PDF全文

杨秋明 《应用气象学报》1998,9(4):410-416

用1973～1994年观测资料,研究了东亚中纬冬季雪盖异常对初夏东半球主要流型随季节变化的影响,同时也分析了多（少）雪年份东半球温带地区30～50天低频振荡强度以及夏季中国降水量分布的差异。结果表明,近20年来冬季东亚中纬雪盖强度呈线性增加趋势且迭加较显著的准2年周期变化,它的变化和初夏500hPa低频流型逐候演变之间同时存在线性和非线性相关,并且多雪时欧亚大陆大部分地区30～50天振荡强度增强,而东北亚地区减小。  相似文献   

地球系统模拟和混沌时间序列   总被引：18，自引：0，他引：18  

刘式达 《地球物理学报》1990,33(2):144-153

地球系统是非线性的系统.为了模拟地球系统,我们就必须了解非线性科学的最新进展.本文从非线性科学角度论述了地球系统模拟中的几个关键问题,如尺度是分层次的,不同尺度之间存在着相似性及标度律,同时也存在差异性及非均匀性.为此还介绍了一些概念:吸引子、分维、信息和熵等.最后本文还说明如何从地球系统中所观测到的时间序列取得地球系统模拟所需要的信息.  相似文献