Characteristics of negative lightning flashes presenting multiple-ground terminations on a millisecond-scale     

X.Z. Kong  X.S. Qie  Y. Zhao  T. Zhang 《Atmospheric Research》2009,91(2-4):381-386

By using a high-speed video camera system (1000 frames s^− 1) in correlation with fast and slow antenna systems, the negative cloud-to-ground (CG) flashes that struck the ground with more than one termination have been analyzed. This kind of stroke, named as multiple-ground terminations stroke (MGTS), was produced by different branches of the same stepped leader during quite a short time. Based on optical images, the 2D progression speed of leader branches was estimated to be in the range (0.9–2.0) × 10⁵ m s^− 1. The distance between adjacent striking points of MGTS was from 0.2 km to 1.9 km. The percentage of flashes with multiple-ground terminations occupied about 15% (9 out of 59) of the total negative CG flashes, with a range of 11%–20% in different areas in China. The time intervals between the two adjacent peaks ranged from 4 μs to 486 μs based on the E-field change caused by the MGTS. The flashes which had multiple striking points on the ground during quite a short time may be a common phenomenon in the lightning discharge process. It might produce more serious damage to facilities on the ground and should not be neglected in the design of lightning protection.  相似文献   

Influence of channel tortuosity on the lightning return stroke electromagnetic field in the time domain     

Zhong-kuo Zhao  Qi-lin Zhang 《Atmospheric Research》2009,91(2-4):404-409

The effect of lightning channel tortuosity on the associated electromagnetic (EM) fields in the time domain is investigated quantitatively from a new point of view. Due to the vanishing of geometric symmetry when taking into account the tortuosity of lightning channels, it is necessary to calculate the associated EM fields in the Cartesian coordinate system. An efficient technique is adopted to produce tortuous lightning channels and then the fractal dimension of the channel is calculated automatically by a program. The results show that at close distances, the dependence of EM fields on azimuth is significant, the ratio of MF peaks at two coaxial points with the channel base may reach about 4 and that of the EF may be larger than 2. With increased distance, the dependence of waveform on azimuth weakens. At distances of 10 km and 100 km, the current peaks derived from the EF peaks show good consistency with the current peak adopted, with an uncertainty less than 25%.  相似文献   

武汉市居民中暑与气象因子的统计特点研究     

何玲玲  陈正洪 《气候与环境研究》2009,14(5):531-536

利用武汉市1994～2006年共13年1464个中暑病例资料和同期逐日气象资料,分别统计逐日中暑人数、日平均中暑人数与气象因子的线性、非线性相关系数,筛选出关键气象因子,建立中暑与多气象因子的非线性模型,制订中暑气象等级标准.结果表明:气温是中暑发生的最关键影响因子,不利气象因子3天或3天以上的累积效应才能导致中暑群发,中暑人数与气象因子呈现非线性关系.建立了日平均中暑人数与前3日平均气温、前3 日平均最小相对湿度的指数模型.将日平均中暑人数划分为5级,并应用该等级标准进行历史样本同代检验和独立样本预报检验,效果较好.  相似文献   

广义极值分布理论在重现期计算的应用   总被引：3，自引：0，他引：3  

陈兴旺 《气象与减灾研究》2008,31(4):52-54

在气候统计学上,常用Weibull、Gumbel、Frechet统计分布函数对极端气候要素的分布进行拟合,广义极值分布理论综合了以上三种极值分布模型,在气候分析中得到了广泛应用。以南昌市年汛期日最大降水量为例,利用广义极值分布理论对其分布进行拟合,并对重现值及其置信区间进行计算,为气候要素极值的统计分析提供了一种新的手段。  相似文献   

基于LLS的多回击地闪及其雷电流幅值分布特征     

王学良  成勤  王清龙  余田野  张科杰  赵涛 《热带气象学报》2021,37(3):309-319

为进一步研究多回击地闪参数分布特征, 以便为雷电防护工程设计和雷电物理研究提供参考, 根据湖北省雷电定位系统(LLS)2007年1月—2018年12月监测资料, 采用计算机编程处理和数理统计方法, 对多回击地闪次数、多重回击次数和不同类型多回击地闪雷电流幅值等参数进行了统计分析。结果表明: 多回击正地闪、负地闪和总地闪次数占其地闪总数的百分比分别为2.06%、34.76%和32.64%, 多重回击次数分别占其回击总数的0.01%、0.42%和0.40%, 多回击负地闪回击次数占多回击总地闪回击总数的99.69%。首次回击强度大于后续回击强度的多回击正地闪和负地闪分别占多回击地闪总数的82.52%和57.87%;在多回击地闪后续回击中, 正地闪约有9%的后续回击强度大于首次回击强度, 负地闪约有20%的后续回击强度大于首次回击强度。多回击正地闪和负地闪中值电流分别为59.30 kA和35.10 kA, 首次回击分别为90.90 kA和40.00 kA, 后续回击中分别为43.90 kA和33.00 kA。首次回击中, 多回击正地闪和负地闪雷电流幅值大于100 kA的累积概率分别为44.06%和4.64%, 首次回击强度大于后续回击强度的多回击正地闪和负地闪雷电流幅值大于100 kA的累积概率最大分别为52.21%和7.94%;后续回击中, 多回击正地闪和负地闪雷电流幅值小于等于40 kA的累积概率分别为41.80%和69.92%, 首次回击强度大于后续回击强度的多回击负地闪, 雷电流幅值小于等于40 kA的累积概率最大为77.71%。多回击正地闪和负地闪后续回击与首次回击中值电流的比值分别为0.48和0.83。拟合得出的不同类型的多回击正地闪和负地闪雷电流幅值累积概率公式, 拟合效果显著; 拟合公式中a值附近的雷电流幅值累积概率与b值呈显著正相关关系。   相似文献   

广州珠江新城地区高建筑物雷电回击磁场分析     

殷启元  黄惺惺 《气象科技》2018,46(2):423-428

对2011—2012年广州高建筑物雷电观测站获取到的雷电回击磁场波形数据进行统计分析,选取14个高建筑物的27次闪电过程(均为负极性地闪,含回击过程112次),其中44%的闪电个例为单次地闪过程。采用小波软阈值去噪法和基础噪声归零法进行数据预处理,分析发现:选取的回击磁场波形均呈现多峰现象,鉴于高建筑物反射峰的影响,本文只统计初始峰值;选取数据的1次闪电回击次数的算术平均值为4.2次,高度200m以下的闪电过程(14次)算术平均回击次数5.1次,高度200m以上的闪电过程(13次)算术平均回击次数3.2次;建筑物越高对磁场峰值的增强作用越显著,击中200m以上的建筑物上雷电首次回击和继后回击磁场峰值几何平均值分别是200m以下的2.2倍和1.5倍;建筑物高度对回击过程磁场波头上升时间影响不大;继后回击过程磁场波头时间远小于首次回击,与回击电场波形特征一致。  相似文献   

图像艺术风格化的研究现状     

邓盈盈  唐帆  董未名 《南京气象学院学报》2017,9(6):593-598

图像艺术风格化作为一个正在蓬勃发展的领域被越来越多的人熟知,也引起了众多学者的研究兴趣.本文总结了图片风格化的发展现状,分析了不同风格化方法的特点,指出了目前风格化方法的缺点,总结了图片风格化的发展趋势,为进一步研究图片风格化提供了方向.  相似文献   

有向拓扑的河系渐变自动绘制算法     

吴伟  李成名  殷勇  郭沛沛 《测绘科学》2016,(12):89-93

河系渐变绘制是地图制图中水系要素表达的重要方面。针对全自动河系渐变研究较少的现状,该文提出一种基于树状约束stroke特征的河系渐变自动绘制算法。该方法在深入分析有向拓扑的数据结构基础上,重点解决河口模式识别、树状约束stroke特征构建、河系层次关系建立、主支流分级渐变等问题,实现全自动河系渐变,并进行实践测试。结果表明,该算法在地图制图过程中无须对河系河源、河口识别、河系分层和河系渐变进行人工干预,自动化程度高,大幅度提升制图效率,渐变效果优于人工绘制效果。  相似文献   

A generalized approach for long-term modelling of extreme crest-to-trough wave heights     

Felice Arena  Diego Pavone   《Ocean Modelling》2009,26(3-4):217-225

This paper deals with the long-term modelling of high sea waves. The solution is given for the return period of sea storms during which an arbitrary chosen number of waves, with crest-to-trough heights exceeding a fixed threshold, occur. This return period is derived starting from the Equivalent Triangular Storm (ETS) model, which associates a triangle to each actual storm and thus represents a significant wave height time series at a fixed location by means of a sequence of triangular storms. The short-term statistics is then applied to investigate the occurrence of large crest-to-trough wave heights during a given storm. Finally, by combining the statistical distribution of significant wave heights, the ETS model and the short-term wave statistics, the solution is given for the return periods R_N and R_N of a sea storm in which N or at least N waves higher than a fixed threshold occur. The values of R_N are then calculated, starting from data of two buoys moored in the Pacific Ocean and in the Mediterranean Sea.  相似文献   

Regularized joint inverse estimation of extreme rainfall amounts in ungauged coastal basins of El Salvador     

Michael J. Friedel 《Natural Hazards》2008,46(1):15-34

A regularized joint inverse procedure is presented and used to estimate the magnitude of extreme rainfall events in ungauged coastal river basins of El Salvador: Paz, Jiboa, Grande de San Miguel, and Goascoran. Since streamflow measurements reflect temporal and spatial rainfall information, peak-flow discharge is hypothesized to represent a similarity measure suitable for regionalization. To test this hypothesis, peak-flow discharge values determined from streamflow recurrence information (10-year, 25-year, and 100-year) collected outside the study basins are used to develop regional (country-wide) regression equations. Peak-flow discharge derived from these equations together with preferred spatial parameter relations as soft prior information are used to constrain the simultaneous calibration of 20 tributary basin models. The nonlinear range of uncertainty in estimated parameter values (1 curve number and 3 recurrent rainfall amounts for each model) is determined using an inverse calibration-constrained Monte Carlo approach. Cumulative probability distributions for rainfall amounts indicate differences among basins for a given return period and an increase in magnitude and range among basins with increasing return interval. Comparison of the estimated median rainfall amounts for all return periods were reasonable but larger (3.2–26%) than rainfall estimates computed using the frequency-duration (traditional) approach and individual rain gauge data. The observed 25-year recurrence rainfall amount at La Hachadura in the Paz River basin during Hurricane Mitch (1998) is similar in value to, but outside and slightly less than, the estimated rainfall confidence limits. The similarity in joint inverse and traditionally computed rainfall events, however, suggests that the rainfall observation may likely be due to under-catch and not model bias.  相似文献