Analysis of microsecond- and submicrosecond-scale electric field pulses produced by cloud and ground lightning discharges     

Amitabh Nag  Brian A. DeCarlo  Vladimir A. Rakov 《Atmospheric Research》2009,91(2-4):316-325

We examined microsecond- and submicrosecond-scale pulses in electric field records of cloud and cloud-to-ground lightning discharges acquired in summer 2006, in Gainesville, Florida. A total of 12 cloud and 12 ground flashes were analyzed in detail, with the electric field record length being 96 or 200 ms and sampling interval being 4 or 10 ns. The majority of pulses in both cloud and ground discharges analyzed in this study were associated with the initial breakdown process and were relatively small in amplitude and duration. The typical durations were an order of magnitude smaller than tens of microseconds characteristic of “classical” preliminary breakdown pulses. We estimated that 26% of the pulses in the 12 cloud discharges and 22% of the pulses in the 12 cloud-to-ground discharges had total durations less that 1 µs.  相似文献   

The intracloud/cloud-to-ground lightning ratio in Southeastern Brazil     

P.E. de Souza  O. Pinto Jr.  I.R.C.A. Pinto  N.J. Ferreira  A.F. dos Santos 《Atmospheric Research》2009,91(2-4):491-499

The intracloud to cloud-to-ground lightning flash ratio (Z) has been estimated for the first time in Southeastern Brazil and in the tropical region using the Lightning Imaging Sensor (LIS) and Brazilian lightning detection network (BrasilDat) lightning data obtained from 1999 to 2005. Geographical variations of Z and their relation to elevation, latitude, precipitation, total lightning density and percentage of positive CG lightning will be discussed. Daily variations of Z will also be presented. The results suggest that Z values are similar to studies outside the tropics and that are influenced by orographic features.  相似文献   

雷击大地密度和等效截收面积计算方法   总被引：1，自引：1，他引：0  

任艳  李家启  覃彬全 《气象科技》2010,38(6):752-757

分析了雷击大地密度传统计算公式中相关参数的局限性,运用IEC62305-2风险管理中的公式对雷电灾害风险分量进行计算分析,提出用闪电定位系统监测到的数据计算雷击大地密度更为合理。根据雷闪的数学模型及雷电流幅值的概率分布特征,对GB50057—1994及IEC62305标准中等效截收面积计算方法进行对比,得出了等效截收面积计算的新方法。  相似文献   

大型海水淡化装置流场数值模拟及其优化   总被引：2，自引：0，他引：2  

庞虹  姚征 《地质灾害与环境保护》2004,15(1):37-41

利用计算流体力学软件Phoenics对海水淡化装置中的闪发腔内的流场进行计算,并分析绕流板的设置对湍流度的影响。由于以往对提高海水淡化装置特别是多级闪发装置(MultiStageFlashMSF)效率的研究多局限于提高热效率的方面,或者是采用化学的方法,而忽视了从流体力学角度通过改变闪发腔内流动情况来提高效率。因此,本文通过对海水淡化装置闪发腔内流动情况的数值模拟,探索提高效率的方法。  相似文献   

Alluvial stratification styles in a large,flash‐flood influenced dryland river: The Luni River,Thar Desert,north‐west India     

Paul A. Carling  Suzanne F. Leclair 《Sedimentology》2019,66(1):102-128

  相似文献   

山区阶梯式河道水流阻力研究   总被引：1，自引：0，他引：1       下载免费PDF全文

罗铭  张焕  丁锐  黄尔  杨奉广 《水科学进展》2019,30(5):719-726

山区阶梯式河道是自然界来水来沙和山区大比降河床相互作用所形成的,其水力特性、河道阻力较为复杂。为了深入研究其阻力机理,从河床结构阻水的角度提出阶梯式结构糙率尺度的概念,得到了适用于阶梯式河道跌落水流的形体阻力系数表达式,并由不同来源的阻力分量构成了新的山区阶梯式河道水流总阻力系数公式。新公式结果表明,通过不同类型河段的野外试验数据,表面泥沙、阶梯形状以及漂石产生的阻力系数分量之和与试验测量总阻力系数数据的误差较小。随着雷诺数和阶梯单元尺寸的增加,河床表面的泥沙肤面阻力系数基本不变,阶梯式结构形成的跌落水流过渡到滑行水流,阶梯形体阻力系数逐渐变小,而较大粒径松散漂石产生的水流阻力系数只随着雷诺数的增大而减小。  相似文献   

An inter‐basin backwater overflow (the Buhai Brook and the Ezer reservoir on the Jijia River,Romania)          下载免费PDF全文

Gheorghe Romanescu  Cristian Stoleriu 《水文研究》2014,28(7):3118-3131

During the last few years, the north‐western part of Romania has been affected by catastrophic floods with most of the watercourses reaching their highest recorded discharges. This study reports the generation of a numerical terrain model and the simulation of a backwater phenomenon at elevation steps according to the volume of water accumulated at the confluence of the Buhai Brook with the Jijia River. The hydrological data are complemented by rainfall data and the careful recording of the flood behaviour during the entire period of its development. The main aim of the study is to identify the causes of the backwater phenomenon and to highlight the material damage inflicted on the town of Dorohoi. At the same time, the study uses cartographic model that was developed to establish which areas are at risk of flooding at various levels of probability. The catastrophic flood began on the Buhai Brook, a slow‐flowing stream that drains the areas to the west of the town of Dorohoi and discharged into the upstream sector of the Jijia confluence. The flood caused two types of backwater waves: one behind the bridges and the houses built on the floodplain and a second that followed the course of the main stem (Jijia) upstream from the confluence, flooding the Ezer Lake, which was created specifically to attenuate such floods. The spillway backwater phenomenon was inter‐basin as it did not occur in a single hydrographic basin. The causes of the catastrophic flash flood and of the inter‐basin backwater overflow are natural but also reflect anthropogenic influence. After the lake filled, the discharge into the Jijia was controlled and the flooding downstream was thus greatly diminished. Though fortuitous, the backwater flooding was important in mitigating the impact of the flood wave from the Jijia River. Copyright © 2013 John Wiley & Sons, Ltd.  相似文献   

Microphysical Characteristics of Extreme-Rainfall Convection over the Pearl River Delta Region,South China from Polarimetric Radar Data during the Pre-summer Rainy Season     

Hao HUANG  Kun ZHAO  Johnny C.L.CHAN  Dongming HU 《大气科学进展》2023,40(5):874-886

During the pre-summer rainy season, heavy rainfall occurs frequently in South China. Based on polarimetric radar observations, the microphysical characteristics and processes of convective features associated with extreme rainfall rates(ERCFs) are examined. In the regions with high ERCF occurrence frequency, sub-regional differences are found in the lightning flash rate(LFR) distributions. In the region with higher LFRs, the ERCFs have larger volumes of high reflectivity factor above the freezin...  相似文献   

太行山地形影响下的极端短时强降水分析   总被引：8，自引：6，他引：2  

王丛梅  俞小鼎  李芷霞  李江波  王秀明 《气象》2017,43(4):425-433

2015年8月2日午夜和2011年8月9日前半夜,在两种不同天气系统背景下太行山东麓都出现了小时雨量超过50 mm的极端短时强降水天气,两次过程都是雷暴先在太行山区触发加强,经过下山2 h先后在丘陵站平山和山前平原站石家庄市区产生极端短时强降水。利用常规探测资料、地面加密观测资料、石家庄SA多普勒天气雷达资料,对不同天气系统背景下太行山特殊地形影响的极端短时强降水成因进行分析。结果表明:偏东气流被南北向的太行山地形强迫抬升,且与下山雷暴出流形成中尺度辐合线触发新的雷暴,雷达回波呈现后向传播特征和列车效应造成局地极端短时强降水。太行山地形通过增强辐合上升运动、增大垂直风切变使雷暴下山加强。不同天气系统强迫下,太行山特殊地形对雷暴发展作用不同。在偏西气流引导下,暖区极端短时强降水由阵风锋触发,具有突发性、降水时间短、伴随风力大的特点,下山雷暴出流加快且与山前偏东风的辐合加强,陆续在丘陵区和山前平原触发对流与下山雷暴合并加强造成极端短时强降水;而在东北气流引导下,回流冷锋和阵风锋共同触发的极端短时强降水具有持续时间较长、降雨总量较大、伴随风力较小的特点,太行山东坡对东北冷湿回流有阻挡积聚作用,东北偏北来的雷暴出流边界西端在迎风坡上强迫抬升使雷暴触发并加强,东北气流遇山后发生气旋性偏转使雷暴出流转向东南下山,与平原的偏东风辐合加强,造成丘陵区和山前平原的总降雨时间更长、降雨总量更大。  相似文献   

基于闪电定位数据的地闪密度修订     

彭国平 《气象科技》2017,45(5):876-881

利用湖北省闪电定位系统(Lightning Location System,LLS)资料,用网格地闪密度数据表征地闪的空间分布,测站距离因子表征探测站布局,对2015年地闪空间分布特征进行分析,结果表明,其密度与因子之间存在负相关,其中雷电流幅值5~30kA的密度分量与因子之间存在显著性相关,大于30kA的密度分量与因子相关不显著。同时发现探测站布局对地闪空间分布的疏密程度有一定的影响,因此有必要对密度进行修订,以消除测站布局的影响。运用线性回归方法及其残差理论,建立了网格地闪密度的修订模型和相对探测效率的统计模型。验证了密度分段修订和不分段修订结果的一致性。通过对理论探测效率和相对探测效率的对比分析,论证了地闪密度修订方法和相对探测效率统计方法的可行性。  相似文献