广西秋季层状云微物理特征分析   总被引：1，自引：0，他引：1  

张正国  卢广献  汤达章  韦增岸 《气象科技》2018,46(3):545-555

利用2012年11—12月在广西进行的11架次飞机云物理探测资料对层状云宏微观物理结构特征进行研究,探讨层状云降水机制。结果表明:广西层状云微物理特征与我国其他地区的存在显著差异。层状云典型的微物理垂直结构为在云下层是由凝结作用生成云滴,随上升气流发展,云滴数浓度、平均直径和液态水含量随高度逐步增加,云滴谱拓宽,谱型向大尺度的方向扩展,至云中上层增大至最大值后随高度减小。冷暖混合云结构的高层云冷云部分的冰相粒子落入暖层后对其微物理结构产生影响,主要是使云滴谱展宽,CIP云滴平均直径垂直分布变幅增大,有利于暖层中碰并过程的启动和发展。层积云微物理水平分布呈现不连续跳跃式变化特征,存在对流泡结构,对流泡内各微物理量高于泡外,云滴谱型向大尺度移动,对流泡结构是层积云形成降水的重要机制。  相似文献   

基于数据挖掘CART算法的区域夏季降水日数分类与预测模型研究     

史逸民  史达伟  郝玲  张银意  王鹏 《南京气象学院学报》2018,10(6):760-765

夏季降水日数的准确预测,对于保障农业、运输业、电力等行业的有序进行具有重要现实意义.利用连云港市气象局提供的1951—2012年夏季降水数据对连云港地区的降水日数特征进行分析,难以直观地发现夏季降水日数随时间分布的规律.为进一步探索降水日数的发生规律,结合国家气候中心网站提供的多种气候因子数据,基于CART决策树算法构建了连云港地区夏季降水日数是否偏多与是否偏少的分类与预测模型.该模型可以发现在多种气候因子不同条件下,夏季降水日数是否偏多（偏少）的规律,模型的分类与预测都具有良好的效果.利用52 a的数据样本训练模型,模型的训练准确率为90.38%（86.54%）,再用剩余10 a数据样本检验模型,测试准确率为80%（80%）,并且得到规则集,方便气象业务人员使用以及决策服务人员参考.同时,为降水日数的预测提供了数据挖掘的新思路.  相似文献   

Coordination of water molecules with Na+ cations in a beryl channel as determined by polarized IR spectroscopy     

J. Fukuda  K. Shinoda 《Physics and Chemistry of Minerals》2008,35(6):347-357

Subtle variations of frequencies in the infrared (IR) absorption spectra of beryl have been predicted based on the coordination between extra-framework cations and water molecules in two orientations (referred to as type I and type II) trapped within the channel. In this study, the polarized IR spectra of hydrated synthetic beryl and natural beryl were measured to clarify the relationships between the frequencies of the absorption bands and the coordination states of type II water. Na⁺ was assumed to be the predominant cation coordinated to type II water in our samples, as determined by chemical analyses. These measurements revealed a clear quantitative linear relationship in absorbance between bands at 3,602 and 1,619 and at 3,589 and 1,631 cm⁻¹. On the basis of experimental and theoretical studies, we assigned these pairs of bands to the ν₁ and ν₂ modes of doubly coordinated type II H₂O and to singly coordinated type II H₂O, respectively. These assignments were supported by IR measurements of annealed natural beryl. We also conducted dehydration studies of natural beryl, in which two observed dehydration peaks, at 600 and 750°C, suggested the dehydration of type I and type II water, respectively.  相似文献   

解地球物理反演中病态方程组的一个方法     

陈震  杨学祥 《吉林大学学报(地球科学版)》1991,(4)

作者根据在计算机数值计算中的经验,提出了在解地球物理反演中常见的病态方程组时,如何确定所用求解方法中的参数问题,取得较好效果。最后用算例作了说明。  相似文献   

以减少地震死亡人数为目标的地震统计决策     

谭承业 《地震研究》1991,14(3):283-291

在地震统计预测研究的基础上,本文提出一种以减少地震死亡人数为目标的统计决策方法,力图把经验性的地震决策引向定量化的地震决策,减少在实际工作中的决策失误。文中用已发生过的地震的资料进行检验,说明该方法的可用性。  相似文献   

灌木植被分布区阻力特性理论及试验研究   总被引：1，自引：2，他引：1       下载免费PDF全文

陆彦  王唯旭  陆永军  宋云涛  鄢栋梁 《水科学进展》1990,31(4):556-564

为探明河道灌木植被分布区阻水规律，对灌木植被主干、分枝产生的水流阻力特性及其定量特征进行研究。提出原型植被体积修正系数和灌木植被水力半径确定方法，理论推导灌木植被阻力系数计算公式，并结合水槽试验建立植被阻力系数与植被水力半径为特征长度的植被雷诺数之间的关系式。研究结果表明：引入原型植被体积修正系数和灌木植被水力半径使灌木植被阻力计算更为准确；植被阻力系数与植被雷诺数之间呈指数函数关系，随植被雷诺数的增加呈单调减小的趋势，与水槽试验结果吻合很好。  相似文献   

Stability analysis of seismic slopes with cracks     

《Computers and Geotechnics》2016

Earthquakes can trigger slope instability, especially in the case of slopes with cracks. Studies of slope stability rarely account for the presence of cracks. In this study, the upper bound limit analysis technique and the pseudo-static method were used to examine the stability of homogeneous slopes with cracks subjected to seismic loading. A series of stability charts for slope inclinations of 2:1 (β = 63.4°), 1:1 (β = 45°), 2:3 (β = 33.7°), and 1:2 (β = 26.6°) (vertical to horizontal) and internal friction angles, φ, of 10°, 20°, 30°, and 40° are presented. These charts should be useful for readily determining the stability number (critical slope height), the critical crack depth, and the region affected by cracks for cracks of known depth but unknown location, cracks of known location but unspecified depth, and cracks of unspecified depth and location.  相似文献   

新疆塔里木河流域洪水过程集聚性及低频气候影响   总被引：1，自引：0，他引：1       下载免费PDF全文

顾西辉  张强  刘剑宇  孙鹏 《水科学进展》2016,27(4):501-511

运用Cox回归模型、月频率法以及离散指数法,研究了新疆塔里木河（塔河）流域8个水文站点POT抽样和5个区域洪水序列时间集聚性特征以及受低频气候变化的影响。结果表明:受气候变化的影响,塔河流域洪水序列呈现显著集聚性特征,洪水发生频率高的时期往往也是大量级洪峰集中发生的时期,这是塔河流域洪灾损失居高不下的主要原因;Cox回归模型拟合的气候指标系数值为正值的站点和区域,气候指标正相位导致相同超过概率的洪水发生时间提前,而相同发生时间的洪水发生超过概率降低,气候指标值为负值时则相反;塔河流域大部分水文站点和区域洪水发生的超过概率均对气候指标变化有较好响应,这一现象有利于塔河流域洪水风险控制与洪灾管理;塔河流域站点洪水序列多无年际集聚性现象,而区域洪水序列的年际集聚性特征显著。  相似文献   

Numerical investigation of wave elevation and bottom pressure generated by a planing hull in finite-depth water     

《Applied Ocean Research》2016

A numerical investigation of the bottom pressure and wave elevation generated by a planing hull in finite-depth water is presented. While the existing literature addresses the free-surface deformation and pressure field at the seafloor independently, this work proposes a direct comparison between the two hydrodynamic quantities. The dependence of the pressure disturbances at the ocean floor from the waves generated at the free-surface by a planing hull is studied for several values of both the depth and hull Froude numbers. The methodology employed is Smoothed Particle Hydrodynamics (SPH), a numerical technique based on the discretization of the continuum fields of hydrodynamics through mesh-less particles. The SPH code herein chosen is initially validated against experimental data for transom-stern flow. Subsequently, numerical simulations are presented for a planing hull in high-speed regimes. The results show a direct correlation between surface wave dynamics and hydrodynamic pressure disturbances at the seafloor as the value of the Froude number is varied. This is assessed by studying the inverse dependence of the low-pressure wake angle with the Froude number and by comparison of SPH results with similar works in the cited literature.  相似文献   

Changes in life cycle of the Ponto‐Caspian amphipod Pontogammarus robustoides at in the northernmost part of its range          下载免费PDF全文

Nadezhda A. Berezina 《Marine Ecology》2016,37(6):1434-1446

The aim of this study was to investigate the dynamics of abundance, population structure and reproductive variables of the invasive Ponto‐Caspian amphipod Pontogammarus robustoides in its northernmost population, located in the Baltic Sea. Pontogammarus robustoides population variables were studied every month from May to October over 7 years (2002–2008) at two locations in the eastern part of the Gulf of Finland, one site in the north and one in the south. Observations of macrozoobenthos were also conducted once per year in July at 12 sites in this gulf during 2002–2014. This was to monitor the distribution area of P. robustoides and its abundance/biomass in different parts of the Gulf. The results showed that P. robustoides is a widely spread species in the Gulf, preferring to colonize stone‐sandy, vegetated and littoral habitats, from the shore to a depth of 5 m, with water salinity of 0.2–3 ppt. This species co‐exists with other amphipods, such as the Baikalian Gmelinoides fasciatus, the North Atlantic Gammarus tigrinus and the native Gammarus spp. The abundance of P. robustoides varied between the two study sites and among years (2002–2008), reaching a maximum level of 1000 ind.·m^?2 for adults and 3000 ind.·m^?2 for juveniles. The temperature‐dependent duration of egg development (embryogenesis) in the amphipod and the annual number of generations in P. robustoides populations varied among years. Three generations were recorded in most years and two generations in the coldest years. Clutch size (or fecundity) was dependent on the body length of female and averaged between 33 and 43 eggs per clutch for females ranging in body length from 11.2 to 12.2 mm. A maximum of 75 eggs were observed in a female with a body length of 16 mm. This paper concludes that life‐cycle variables change when P. robustoides spreads from the southern (Ponto‐Caspian region) to northern (Baltic Sea) range areas. In the studied northernmost location, the fecundity and number of generations of this amphipod were 1.5–2‐fold lower compared with the more southern locations. In addition, these variables and P. robustoides abundance were different between the coldest and warmest years at study sites that testify about their distinct dependence on local environmental conditions; further changes in life cycle of this species may be expected together with current climate warming.  相似文献