Occurrence,shape and movement of daily rainfall in the Huai Basin,China     

Cecilia Svensson 《水文研究》1999,13(8):1197-1215

The upper reaches of the Huai River in Central China are located in the East Asian monsoon region. Strong seasonality, as well as large interannual variability of rainfall, causes floods and an uneven supply of water. In order to conserve the water and mitigate the floods, dams and flood protection structures are constructed. Their design requires information about the rainfall. Daily observations from 1957 to 1986 from 78 rain gauges were used to study shape, orientation, movement and geographical and seasonal occurrence of storms in the 79 000 km² study area. The rainfall characteristics were described using graphical plots, cross‐ and autocorrelation. Storms larger than 50 mm/day were found to occur from February to November, whereas storms exceeding 350 mm/day were confined to the main rainfall season from late June to mid‐August. The southern part of the study area experienced a break in the rainfall season in late July, corresponding to the seasonal northward shift of the rain belt. A weekly periodicity of 7–8 days for rainfall was found during June–July, but not during August–September. During the whole period June–September, the spatial pattern of daily rainfall revealed an elongated shape, more pronounced during June–July than August–September. The rainfall area was orientated approximately from WSW to ENE during the whole period, and showed an anticlockwise rotation of about 16° per day during June–July. The cross‐correlation analysis revealed that the rainfall area moved about 100 km/day eastward. These results and an investigation of meteorological maps indicate that the spatial correlation pattern of daily rainfall is produced by cold fronts on the Mei‐Yu front. Suggestions are made as to how to use the results for the construction of design rainfalls in the study area. Copyright © 1999 John Wiley & Sons, Ltd.  相似文献   

2011年6月江西省北部一次大暴雨天气过程成因分析          下载免费PDF全文

孙素琴  郑婧  许爱华  陈云辉 《气象与减灾研究》2015,38(1):25-36

利用常规气象观测资料、高时空分辨率TBB资料以及NCEP/FNL再分析资料,对2011年6月14—15日江西省北部梅雨锋暴雨过程进行了天气分析。同时,利用中尺度数值模式WRF对此次梅雨锋暴雨过程进行数值模拟,分析暴雨的中尺度系统结构特征。结果表明:稳定的环流形势下,500 h Pa低槽后部冷空气与强盛的西南暖湿气流在江南北部持续对峙,使得暴雨区稳定维持在江西省北部。低层充沛的水汽供应、强的热力不稳定及强烈的天气尺度、中尺度辐合和地形抬升是此次暴雨产生的有利环境场和触发条件。锋区及其附近的锋生过程与强降水密切相关,冷暖气流在地面至对流层中低层的交馁,激发正涡度柱沿锋区倾斜爬升,强烈的上升气流穿越锋区激发大量不稳定能量释放。超低空急流的脉动和稳定维持为暴雨发生的有利水汽输送机制,高低空水平距离的缩短有利于高低空急流的耦合、垂直运动的发展和降水强度的加强。强降水区上空β中尺度对流扰动在冷、暖气流对峙区内不断生成、发展、东移,加之局地地形等作用致使大暴雨的发生。  相似文献   

Gust Front Statistical Characteristics and Automatic Identification Algorithm for CINRAD          下载免费PDF全文

ZHENG Jiafeng  ZHANG Jie  ZHU Keyun  LIU Liping  LIU Yanxia 《Acta Meteorologica Sinica》2014,28(4):607-623

Gust front is a kind of meso-and micro-scale weather phenomenon that often causes serious ground wind and wind shear. This paper presents an automatic gust front identification algorithm. Totally 879 radar volume-scan samples selected from 21 gust front weather processes that occurred in China between 2009 and 2012 are examined and analyzed. Gust front echo statistical features in reflectivity, velocity, and spectrum width fields are obtained. Based on these features, an algorithm is designed to recognize gust fronts and generate output products and quantitative indices. Then, 315 samples are used to verify the algorithm and 3 typical cases are analyzed. Major conclusions include： 1） for narrow band echoes intensity is between 5 and 30 dBZ, widths are between 2 and 10 km, maximum heights are less than 4 km （89.33%are lower than 3 km）, and the lengths are between 50 and 200 km. The narrow-band echo is higher than its surrounding echo. 2） Gust fronts present a convergence line or a wind shear in the velocity field;the frontal wind speed gradually decreases when the distance increases radially outward. Spectral widths of gust fronts are large, with 87.09% exceeding 4 m s-1 . 3） Using 315 gust front volume-scan samples to test the algorithm reveals that the algorithm is highly stable and has successfully recognized 277 samples. The algorithm also works for small-scale or weak gust fronts. 4） Radar data quality has certain impact on the algorithm.  相似文献   

盛夏杭州湾一次海风锋触发雷暴的数值模拟分析          下载免费PDF全文

吴福浪  李晓丽  於敏佳  张晶晶  刘耀杰 《大气科学学报》2019,42(4):581-590

利用常规气象观测资料、多普勒气象雷达资料、浙江省自动站加密资料、NCEP/FNL再分析资料,结合高分辨率中尺度数值模式WRF对杭州湾地区2016年7月28日一次海风锋触发雷暴天气的发生、发展演变特征进行数值模拟。结果表明:1)海风锋是此次强雷暴天气过程的主要触发系统。2)中尺度模式WRF较好地模拟出此次雷暴过程的降水和低层风场、温度场分布以及海风锋水平垂直结构。3)海风锋对局地比湿及涡度特征的加强有明显的促进作用,为雷暴的发生发展提供有利的水汽和动力条件。4)分析对流参数演变曲线的突变位置,对雷暴发生的时间有一定的指示和预报意义,杭州湾南侧单纯的海风锋也可以触发雷暴的发生发展。  相似文献   

砂质底质潮汐水道均衡态模拟初探   总被引：4，自引：2，他引：2  

谢东风  高抒  汪亚平 《海洋学报》2006,28(6):86-93

以过程模拟法探讨了发育在砂质堆积体上的潮汐水道的均衡态问题.在潮汐作用为主导、初始状况为平坦海底、底质粒度均一等条件下,利用修正的Bagnold推移质输沙率公式和沉积物连续方程,建立砂质潮汐水道均衡态的一维模型.数值实验结果表明,潮汐水道达到均衡态的时间尺度为10a以上,水道形成的早期冲刷速度较快,随着时间的推移,冲刷减缓.从水道冲刷出来的物质在水道前方形成堆积体.潮汐水道的演变受控于水动力变化和沉积物冲淤的负反馈机制,水道均衡态主要与沉积物粒径、涨落潮流速、历时、流速沿水道轴向分布的组合特征有关.流场特征决定了水道均衡态的形态;在沉积物组分均一的情况下水道均衡深度与潮流流速呈正相关;达到均衡态的时间尺度与沉积物粒径、涨落潮历时、流速的变化以及水道规模有关.沉积物临界起动流速随深度的变化对水道均衡态有较大影响.  相似文献   

滩涂围垦区的PRED关系--以慈溪市为例   总被引：1，自引：0，他引：1  

冯利华  鲍毅新 《海洋科学》2006,30(4):88-91

根据历史数据和2020年全面建设小康社会的标准,利用系统动力学(SD)模型,仿真研究了慈溪市未来政策实施后PRED(滩涂围垦区的人口、资源、环境和发展不协调简称为PRED问题)关系的不同情况。同时指出,对于慈溪市来说,单方面追求经济的快速发展、以牺牲环境作为代价的方案1和把环境保护作为第一目标、经济慢速发展的方案2都是不可取的,只有人口、资源、环境和发展同时兼顾的方案3才是首选方案。  相似文献   

强震前形变潮汐异常判识与机理研究   总被引：4，自引：0，他引：4  

张晶  陈荣华  杨林章  吉平 《地震学报》2006,28(2):150-157

通过对永胜倾斜、侯马应变数字化固体潮汐观测资料的分析研究,认为当孕震系统进入失稳的临界状态时,微量级的形变突变可能受到引潮力的触发作用. 阶变异常与引潮力的方向、断层走向的剪应力的大小和方向有一定的相关性. 本文首次将形变异常与附加引潮力的关系进行研究,以探索临震前形变异常的物理机制及判识方法.   相似文献   

一次强对流天气综合分析   总被引：2，自引：2，他引：0  

吉惠敏  冀兰芝  王锡稳  李文莉 《干旱气象》2006,24(2):12-18

2004年7月4日下午,甘肃河东出现强雷阵雨天气并伴有冰雹。从大尺度环境场、物理量场特征、多普勒雷达回波特征3方面综合分析本次强对流天气的成因。本次过程在500 hPa高空环流形势场上呈典型的西北气流型,冷平流随高度增加使不稳定层结得以建立和维持。干冷空气冲击高原东侧到甘肃中部的能量锋,触发了强烈的对流。根据雷达回波演变过程看出,冰雹是由多单体风暴造成的,在径向速度图上可分析出γ中尺度气旋性旋转流场。  相似文献   

多尺度合成的降水临近预报技术   总被引：3，自引：1，他引：2  

王珏  张家国  万玉发 《气象科技》2008,36(5):524-528

基于我国新一代多普勒天气雷达观测资料,以梅雨锋等大范围降水为主要研究对象,研究了降水临近预报方法.根据暴雨回波的多尺度特征等,研究暴雨回波的尺度滤波,分割、匹配等处理技术;根据不同尺度回波生命史来约束其预报时效,得到分尺度下的降水预报场,实现暴雨回波多尺度的合成降水量临近预报;将分尺度与不分尺度降水预报结果进行了比较.结果表明,针对大范围强降水多尺度合成的降水量临近预报方法,因不同尺度的回波外推考虑了各自运动的特性及其生命史的差异,预报精度有所提高.  相似文献   

Tidal effects of a massive spheroidal halo on an inner spheroidal contracting visible body: Application to an evolutionary disk-galaxy model     

R. Caimmi  L. Secco 《Astronomische Nachrichten》1993,314(6):399-412

The effects of the tidal interactions between two coaxial, homogeneous spheroids, one (the “Brigt Component”: B) completely embedded in the other (the “Dark Halo”: D), along a quasi-static contraction, are considered. The aim is to look how the dynamical properties and the final morphology of the B subsystem may be affected by the presence of the D component. Three initial configurations are considered: the quasi-spherical “Dark Halo” D coincides with the “Visible Component” B (case C); D is flatter than B but the two spheroids have the same semiminor axis (case N); no D component is assumed; the “visible” spheroid is single (case S). The application to an evolutionary disk-galaxy model is considered under some simple assumptions: i) in cases C and N the spheroidal halo is massive (mass ratio “dark”/“bright” about ten) and dissipationless. For a mass ratio like this, the tidal interaction of the B component over D turns to be negligible in the course of the contraction; adding to that the lack of dissipation, it appears plausible to take the D component as frozen along the evolution; ii) the degree of anisotropy and the angular momentum of B, J_B, are conserved. The conservation of J_B provides us the time-independent relationship among the key physical quantities and gives the possibility to draw the evolutionary tracks on the plane (axis ratio σ_B, semimajor axis a_B) without any explicit time-scale; iii) the global “star formation rate” is parametrized according to a simple “Schmidt power law” proportional to the square of gas density. At every step of the quasi-static contraction, the structure is determined by the tensor virial theorem extended to a double configuration. The model is very idealized, particularly because there are no available tidal gravitational terms other than for the case of two homogeneous. Nevertheless, the method based on the tensor virial appears powerful to gain insight into the correlations among the physical quantities involved and into their trend along the evolution. One of the main result is a clear indication of a leading role played by the axis ratio of the “Dark-Halo” component which might be, to the extent that this simple picture can be compared with a real galactic system, a possible new physical parameter to be added to mass and angular momentum for separating spirals from S0 galaxies.  相似文献