基于列车运行网络的中国城市中心性分析

 本文基于铁路运行网络,利用复杂网络分析方法中的中心性评价指标,对城市在铁路网络中的中心性进行了分析。我们根据列车时刻表基于L空间模型,构建了铁路运营网络,计算了铁路运营网络中节点城市的不同中心性指标,包括度中心性、邻近中心性和介中心性。这3个指标从不同角度衡量了城市在铁路运输网络中的地位和功能,我们分析了这3个中心性指标的空间分布特征及相关性,并探讨了中心性指标与城市发展之间的关系,进一步揭示铁路网络结构对城市发展的影响。     

A PREDICTION SCHEME FOR THE PRECIPITATION OF SPR BASED ON THE DATA MINING ALGORITHM AND CIRCULATION ANALYSIS

Based on the 74 circulation indexes provided by National Climate Center of China (hereinafter referred to as NCC) and the 24 indexes compiled by NOAA, the study used the C4.5 algorithm in data mining to establish a decision tree prediction model to predict whether the Spring Persistent Rains (hereinafter referred to as SPR) of 55 years (from 1961 to 2015) is more than the normal, and obtained 5 rules to determine whether the SPR is more than the normal. The accuracy rate of the test set, namely “whether the SPR is more than the normal”, is 98.18%. After evaluating the model by conducting ten 10-fold cross validations to take the average value, the test accuracy rate gained is 84%. There are differences between the three types of years with a SPR more than the normal when it comes to intensity and distribution. In spring, they have respective anomalous 850hPa monthly mean wind fields and water-vapor flux distribution, and 700hPa forms the zone where the vertical speed is anomalously negative. As indicated by the results, the SPR prediction model based on the C4.5 algorithm has a high prediction accuracy rate, the model is reasonably and effectively constructed, and the decision rules take comprehensive factors into consideration. The anomalous rainfall and circulation distribution characteristics obtained based on the decision classification results provide new ideas and methods for the climatic prediction of SPR.     

中国大范围持续性极端低温事件的一类平流层前兆信号

本文利用NCEP/NCAR逐日再分析资料,研究了中国大范围持续性极端低温事件(EPECE)的平流层前兆信号及其对对流层环流异常的影响。结果表明,在52个EPECE中,有17个EPECE具有一类共同的平流层前兆信号:(1)在EPECE发生前10天左右,在巴伦支海一带的100 hPa位势高度场呈现较强的正距平特征;(2)随后,该正异常环流逐渐向东移动,并在EPECE发生的前5天左右,使贝加尔湖西北侧200 hPa纬向风显著减弱。本文据此提出了关于EPECE平流层前兆信号的两个判别条件,并以这两个判别条件对1949～2009年冬季(11月至次年3月)所有逐日低频场进行了后查和检验。结果表明,上述两个判别条件对EPECE的发生日期具有一定的预测能力。本文进一步通过位涡(PV)反演探讨了平流层前期异常环流如何影响EPECE发生的物理机制。分析表明,巴伦支海附近的平流层中低层PV异常有利于该地区对流层中上层正高度异常的维持,后者强度的25%来源于前者的作用。     

副热带东南太平洋海温对东北夏季降水的影响及可能机制

诊断分析表明,前期副热带东南太平洋海温尤其是前春海温与东北夏季降水存在持续稳定的负相关关系。无论是在年际时间尺度还是年代际尺度上,冬、春、夏季海温演变趋势与降水均呈反位相。尺度分离结果显示,关键区海温与降水的显著负相关主要依赖于其年代际分量,但年际分量也起到较重要贡献。相关分析和合成分析结果都发现,当副热带东南太平洋海温偏低时,其上空可激发出反气旋式距平风场,而在关键区海域西北部激发出气旋式距平环流。同时在所罗门群岛和菲律宾南部分别出现反气旋式和气旋式距平环流。西太平洋副热带高压(副高)位置较常年偏西,副高区为反气旋式距平环流。在东北地区西侧则为气旋式距平环流。在这样的环流背景下,副高西侧的南风加强了源自南海和西太平洋的暖湿气流和北方冷空气在东北地区的交汇,从而使东北夏季多雨。反之,当东南太平洋海温偏高时,其激发的气旋及反气旋距平中心和偏低年刚好相反,副高位置偏东,其西侧的南方水汽输送偏弱,同时东北冷涡也偏弱,冷暖空气汇合形成的低空辐合弱,东北降水因此偏少。这表明,副热带东南太平洋海温异常时确实能激发出一个从关键海区到东北地区的跨越南北半球的气旋-反气旋交替波列,引发北半球中高纬度大气环流异常,从而影响东北夏季降水。     

Correlation analysis of persistent heavy rainfall events in the vicinity of the Yangtze River valley and global outgoing longwave radiation in the preceding month

Based on the National Oceanic and Atmospheric Administration (NOAA) daily satellite dataset of global outgoing longwave radiation (OLR) for the period of 1974--2004 and the NCEP-NCAR reanalysis for 1971--2004, the linkage between persistent heavy rainfall (PHR) events in the vicinity of the Yangtze River valley and global OLR leading up to those events (with 1- to 30-day lag) was investigated. The results reveal that there is a significant connection between the initiation of PHR events over the study area and anomalous convective activity over the tropical Indian Ocean, maritime continent, and tropical western Pacific Ocean. During the 30-day period prior to the onset of PHR events, the major significantly anomalous convective centers have an apparent dipole structure, always with enhanced convection in the west and suppressed convection in the east. This dipole structure continuously shifts eastward with time during the 30-day lead period. The influence of the anomalous convective activity over the tropical oceans on the initiation of PHR events over the study area is achieved via an interaction between tropical and extratropical latitudes. More specifically, anomalous convective activity weakens the Walker circulation cell over the tropical Indian Ocean first. This is followed by a weakening of the Indian summer monsoon background state and the excitation and dispersion of Rossby wave activity over Eurasia. Finally, a major modulation of the large scale background circulation occurs. As a result, the condition of a phase-lock among major large scale circulation features favoring PHR events is established over the study area.     

Temporal and Spatial Distributions of the Spring Persistent Rains over Southeastern China

The spring persistent rains (SPR) over southeastern China (SEC) is a synoptic and climatic phenomenon that is unique in East Asia. Su cient evidence proves that it results from the mechanical and thermal effects of the giant Tibetan Plateau (TP), but its temporal span and spatial distribution are not clear at present.A climatological analysis of the NCEP/NCAR circulation and sensible heat data shows that at the 13th pentad of the solar year (1st pentad of March) there are remarkable increases in the sensible heating over the main and southeastern part of the TP, the southwesterly velocity over the southeastern flank of the TP and SEC, and rainfall over SEC, indicating the onset of the SPR.However, after the 27th pentad of the solar year (3rd pentad of May), these variables, except for the sensible heating over the main part of the TP, decrease rapidly. The ridge line of the subtropical high in the mid-low troposphere over the South China Sea (SCS) slopes northward instead of southward as before. The rain belt center over SEC shifts to the SCS and the SCS monsoon breaks out, indicating the end of the SPR. Hence, it is reasonable to define the SPR temporal span from the 13th to 27th pentad of the solar year. Data analysis and numerical sensitivity experiments show that, although the warm and cold airs converge at about 30°N in the SPR period, the distribution and intensity of the SPR rain belt are obviously in influenced by the topography of the Nanling and Wuyi Mountains (NWM). The mountains can block and lift cold and warm airs, strengthening frontogenesis and rainfall. As a result, the axis of the SPR rain belt is superposed over that of the mountain range. Accordingly, the spatial distribution of the SPR extends over most of the SEC, more speci cally, to the south of the middle and lower reaches of the Yangtze River (30°N), and to the east of 110°E.     

Dynamic responses of a poroelastic half‐space from moving trains caused by vertical track irregularities

The vibrations of railway tracks on a poroelastic half‐space generated by moving trains are investigated through a vehicle–track–ground coupling model. The theoretical model incorporates a vehicle, a track, and a fully saturated poroelastic half‐space soil medium. The source of vibration excitation is divided into two components: the quasi‐static loads and the dynamic loads. The quasi‐static loads are related to the static component of the axle loads, whereas the dynamic loads are due to the dynamic wheel–rail interaction. A linear Hertizian contact spring is introduced between each wheelset and the rail to consider the dynamic loads. Biot's dynamic theory is used to characterize the poroelastic half‐space soil medium. Using the Fourier transform, the governing equations for the track–ground system are solved and the numerical results are presented for a single axle vehicle model. The different dynamic characteristics of the elastic soil medium and the saturated poroelastic medium are investigated. In addition, the different roles of the moving axle loads and the roughness‐induced dynamic loads are identified. It is concluded that the vibration level of the free field off the track predicted by the poroelastic soil medium is smaller than that predicted by the elastic soil medium for vehicle speed below the Rayleigh wave speed of the poroelastic half‐space, whereas it is larger for vehicle speed above the Rayleigh wave speed. The dynamic loads play an important role in the dynamic responses of the track–ground system. Copyright © 2010 John Wiley & Sons, Ltd.     

ASIA-PACIFIC WINTER LFO STRUCTURE AND LOWFREQUENCY VORTEX ACTIVITY FEATURES*

Based on the winter 1984/1985 ECMWF grid point data subjected to the 30-60 day band-pass filtering and composite analysis,a study is undertaken of the LFO(low-frequency oscillation) structure in the eastern Asian westerly jet entrance and exit regions and the Asia-Pacific low-frequency vortex activity characteristics.Results show that zonal wind oscillations on both sides of the jet core are in anti-phase,in close relation to the E-W displacement of the core.Ranging in NW-SE direction is a low-frequency vortex train(LFVT) emanating from Ural via central Asia to East Asia.A low-frequency vortex of Ural origin,when reaching around 50°N,80°E,is split into two parts,one travelling eastward and the other southward,and finally they arc connected cyclonically or anticyclonically at low latitudes,forming a vigorous low frequency cyclone or anticyclone in the eastern part of China mainland,completing a full cycle of the LFVT.Further,observed in the central Pacific are a meridional LFVT and a cyclone/anticyclone couplet looping in a counterclockwise sense,giving rise to the LFVT phase shift over this region.     

波列振幅P em>-Sem>曲线测桩法

叙述一种新的大应变检测单桩竖向承载力的方法. 用重锤或小型火箭筒冲击桩顶，用检波器记录振波图. 引入应变（变形力）的高次项，从理论上证明当为大位移大应变， 即桩相对于土体产生整体滑动时，位移、速度和加速度则不能经过简单积分加速度和微分速度得到，即它们为非线性关系. 由此导出:通过波列振幅计算力（P）和位移（S）,并作（动态）P-S曲线、确定屈服点，进而阐述确定单桩竖向承载力的方法，并利用静载荷试验检验动测结果和确定动静P（Q）S曲线的相关常数.