共查询到19条相似文献，搜索用时 156 毫秒
1.
云闪放电通道的光谱及温度特性 总被引：1，自引：0，他引：1
利用无狭缝光栅摄谱仪在西藏地区进行了自然闪电的光谱观测试验,首次拍得了7幅分辨比较清晰的云闪通道的光谱,并与地闪光谱相对比,对云闪光谱的结构特征进行了分析．结果表明,这些云闪光谱显示出两种不同的结构特征：一类与地闪光谱具有相似的谱线结构,而另一类与以往得到的地闪光谱完全不同．同时,与同一地区的地闪光谱相比,在这些云闪光谱中记录到的激发能较高的OII离子谱线比较多．依据谱线波长和相对强度等信息,计算了放电通道的温度,并对通道不同位置处的温度分布进行了分析．从光谱结构和通道温度的特征推断：与地闪相比,在一次闪击过程中,云闪通道内发生的物理过程变化速度更快、变化范围更大;两类光谱对应的云闪通道放电特性有一定的差异． 相似文献
2.
依据在中国西藏高原地区得到的6幅云闪放电通道的光谱,由谱线波长、相对强度和跃迁几率等信息,结合等离子体理论,计算了云闪放电通道的温度和电子密度;进而,利用Saha方程、电荷守恒和粒子数守恒方程,得到了粒子处于各电离级上的数密度、通道质量密度、压强和平均电离度等参数,并对云闪通道内部粒子数分布特点进行了分析.结果表明,与地闪回击通道类似,云闪通道接近于完全电离,通道内部以单次电离的离子为主,且NII离子数密度最高.具有较高温度的通道位置处,中性和一次以上电离离子数密度的绝对值和相对值都较高,但是,不同温度下NII、OII、ArII粒子的相对浓度变化不大.与地闪回击通道不同,云闪同一放电通道内不同位置处粒子数密度差异较大,且沿通道没有显示规律性变化,通道压强从零点几到几兆帕. 相似文献
3.
依据高速摄像系统记录的一次多接地点云对地闪电过程的光学图像和同步的辐射电场变化资料,分析了其先导的传输和电场变化特征、接地行为,估算了先导发展的速度,并探讨了它与相应的回击间隔时间、峰值电流之间的关系.结果表明:该多接地闪电首次回击3个明显接地点间的平均距离约为512.7m,相应电场快变化脉冲的平均间隔为3.8μs.梯级先导脉冲间的平均间隔比普通单接地闪电的相应值小.从光学图片上看,该闪电有左右两个主通道,左通道在首次回击强放电之后有明显的直窜先导到达地面附近,但没有形成回击;而右通道出现了更为少见的现象,继后回击R2与相应直窜先导的时间间隔很长,在先导到达地面约2.1ms后才发生回击.这一现象应该与首次回击放电较强,接地点附近的电荷没能及时补充有关.左右通道梯级先导的发展速度分别约为1.23×10~5和1.16×10~5m s~(-1).左通道梯级先导一个次分支未能接地、发展为企图先导,这与连接它的主通道分支太多有关;另外,该次分支的发展方向与大气电场方向接近垂直,不利于电荷的传输.5次继后回击均发生在右通道,其直窜先导的二维速度均在常见的数值范围内.直窜先导发展速度与相应继后回击的峰值电流正相关. 相似文献
4.
利用闪电宽带干涉仪系统对地闪先导-回击过程的观测研究 总被引：2，自引：2，他引：2
利用闪电宽带干涉仪系统1999年在广东的观测资料, 对地闪预击穿、梯级先导及回击过程进行分析研究, 结果表明: 这种新型的辐射源定位系统能够再现闪电通道结构和电磁辐射源随时间演变的二维图像(方位角和仰角). 闪电辐射主要由负击穿过程产生, 地闪预击穿阶段闪电通道比较集中, 几乎没有分杈, 辐射源主要出现在通道头部; 而梯级先导后期辐射源定位比较离散, 有较多的分叉通道, 辐射源出现在具有一定长度通道段内, 该通道段高度随着先导向地面的发展逐渐降低. 预击穿过程和梯级先导期间均有一些快速负流光过程连续地从闪电起始区域或更远的位置开始, 沿已形成的通道发展, 为闪电通道进一步向前发展补充电荷, 其速度比闪电通道发展的平均速度约快一个量级. 相似文献
5.
正地闪发展的时空结构特征与闪电双向先导 总被引：1，自引：0，他引：1
利用闪电VHF辐射源定位系统的观测资料, 对正地闪三维时空发展特征进行了分析, 结果表明正地闪过程大致可分为三个阶段, 在回击之前有较长的云内发展过程, 平均持续时间为370 ms, 传输速度为105 m/s量级, 辐射强度与负地闪梯级先导辐射强度相当, 这一期间闪电是以负极性击穿过程在云中正电荷区发展, 通道沿水平方向延伸, 较少分叉;回击之后闪电在云内快速传输, 比回击前的发展速度快约2倍, 辐射点较少且比较弥散, 但辐射强度增强, 对应于连续电流过程, 并包含有多个正极性快脉冲;在闪电的最后阶段, 传输速度与回击前的传输速度相当, 辐射点主要集中在闪电通道的顶端. 与负地闪的时空发展特征存在明显的差异. 正地闪的辐射点均发生在云内正电荷区, 没有探测到回击之前的正先导过程所产生的辐射. 正地闪持续时间平均为730 ms, 持续时间在500~600 ms的闪电占总数的43%. 90%正地闪只有一次回击, 最多有4次回击, 回击电流峰值最大为70 kA, 最小为11.5 kA, 平均为36.5 kA, 大于40 kA的约有40%. 相似文献
6.
基于时差法三维定位系统对闪电放电过程的观测研究 总被引：3，自引：0，他引：3
系统介绍了自行研制的基于GPS同步和时差法定位技术的闪电VHF辐射源三维定位系统以及山东北部地区闪电过程同步观测分析,成功获得了雷暴中闪电通道辐射源三维时空发展物理图像.并结合地面的快电场变化资料,对典型负地闪、正地闪和云闪放电通道的三维时空演变过程进行了分析,结果表明,正、负地闪激发传输过程不同,典型负地闪的预击穿过程发展速度约为5.2×104m/s,被初始负击穿引发的向下梯级先导传输过程发展速度约为1.3×105m/s;正地闪初始阶段也是激发负流光传输,以优势水平方向在正电荷区内传输,并为始发点积累正电荷,从而触发向下正流光传输.重点分析了一次由双极性窄脉冲事件(NBP)引发的云内闪电三维放电过程,该脉冲发生在约10.5km的高度上即上部正电荷区域内,同时引发云内放电通道水平向周围扩展,产生大量击穿辐射源,双极性窄脉冲辐射峰值强度值高达16.7kW,而普通闪电辐射源功率一般在100mW～500W范围内.与经典云闪完全不同,此类新型云闪及其三维传输过程在国内第一次被发现.文章还讨论了其可能的触发机制. 相似文献
7.
用无狭缝光栅摄谱仪,获得了青海西宁地区云对地闪电首次回击过程400～700nm波 长范围的光谱,并首次在闪电的单次回击光谱中记录到了波长为604.6nm和619.4nm的谱线. 将原子结构的理论应用于闪电光谱的研究,用多组态Dirac Fock方法,计算了有关光谱线 的 波长、振子强度以及相应的激发态能量等参数,理论与试验观测资料进行比较分析后发现, 高原地区闪电首次回击光谱的结构及跃迁特性与其他地区有明显的区别,除NII离子n=3 的低 激发态产生的跃迁谱线外,激发能量为13～14eV左右的中性NI和OI的跃迁增多,但很难观测 到OII离子的跃迁谱线. 相似文献
8.
雷暴云内闪电双层、分枝结构的数值模拟 总被引：2，自引：0，他引：2
试验了一种逃逸启动、双向随机发展的放电参数化改进方案, 并进行了12.5 m的高分辨率、二维雷暴云数值模拟试验, 模拟再现的雷暴云内闪电特征在通道扩展范围和双层、分枝结构以及与位势阱位置的相互配合等方面与实际VHF源定位观测资料分析结果是一致的. 进一步发现: (1) 闪电在雷暴云内相邻的正、负电荷区边界附近触发后, 负先导向正电荷区发展、正先导向负电荷区发展. 存在正负两种极性的云闪, 他们的极性由云中相邻正、负电荷累积区位置的上下配置决定. (2) 电荷累积区的空间分布制约着闪电的空间范围. 云闪几乎遍及其所传播的电荷堆, 遭遇到局域性、与通道极性相同的电荷堆时, 通道将转向、绕开该电荷堆. (3) 电位的空间分布形态同样制约着闪电通道传播方向和几何结构: 先导通道进入正或负位势阱之前沿着最大电位梯度方向传播; 当先导通道穿过它们的中心之后通道更趋于电位变化缓慢的地方发展. (4) 云闪通道在穿过电荷累积区中心以前, 有较好的分形特征, 幂指数约为1.45; 而其后向低电荷浓度地区延伸时, 幂指数随着半径增加而减小. (5) 放电结束后通道感应生成的异极性电荷沉积在正、负先导通道经过的区域, 形成新的、复杂的云内电荷空间分布, 位势极值可由200下降到20 MV. 相似文献
9.
闪电活动在时间和空间尺度上都有很大的可变性. 本文利用热带降水测量计划（TRMM）卫星上携带的闪电探测系统获取的闪电定位资料首次对一些典型地区的闪电活动进行了对比分析. 研究发现不同地区的闪电活动无论在闪电频数或放电强度方面都有很大的差别，海洋上的闪电活动频数与陆地上的闪电活动频数可相差几十倍；不同地区闪电活动的多少不仅取决于该地雷暴日数的多少，更重要的还取决于该地每次雷暴过程闪电频数的多少；不同地区的闪电放电强度有随闪电频数增加而减小的趋势. 进一步研究还表明，不同地区闪电光辐射能的不同可以用对流最大不稳定能量（ECAPE）来解释，闪电放电强度与ECAPE之间存在非常好的线性正相关；而闪电活动频数对ECAPE的响应则与闪电光辐射能不同，二者之间没有发现明显的相关. 相似文献
10.
中国主要土壤高光谱反射特性分类与有机质光谱预测模型 总被引：18，自引：0，他引：18
土壤可见-近红外漫反射光谱是当前对地遥感观察和土壤近地传感器研究的重要方向,同时也被认为是土壤数字制图、精确农业和土壤资源调查等方面最重要的数据获取技术.从中国西藏、新疆、黑龙江、海南等地采集16种土类的1581个土壤样本,经干燥过筛后统一采用ASD光谱仪测量了其室内可见-近红外反射光谱(350~2500 nm).对所有的土壤光谱数据采用Savitzky-Golay平滑加一阶微分进行转换,来减少大样本数据受到实验室光学测试环境条件差异的影响,然后对数据进行主成分变换降维处理.引入模糊k-means方法进行大样本光谱数据的最佳分类数目计算,并将中国土壤光谱数据分成五类,各自代表了不同的土壤矿物和有机组分,主要类型与国际同行类似成果有可比性.最后提出了采用土壤光谱分类方法结合偏最小二乘回归法(PLSR)方法建立土壤有机质的光谱分类-局部预测模型,结果比未分类直接采用PLSR方法的一阶微分-全局预测模型的精度有了显著提高,其预测模型的R2和RPD两个指数分别从0.697和1.817提高到0.899和3.158. 相似文献
11.
Spectra of seven cloud lightning discharges are reported for the first time after captured with a Slit-less Spectrograph on
Chinese Tibet Plateau. The structural characters are analyzed and compared with the spectra of cloud-to-ground lightning,
and the results indicate that the spectra of cloud lightning show two different kinds of structure characteristics. One has
the similar structure as those of cloud-toground lightning discharge, and the other is absolutely different. Meanwhile, more
lines of OII with high excited energy are recorded in the spectra of cloud lightning discharge in comparison with that of
cloud-to-ground lighting happening in the same region. Temperatures at different positions are calculated and temperature
characteristics of these two sorts are analyzed, based to the wavelength, relative intensities and other transition parameters.
We suggest that the physical process in the cloud discharge channels changes with much more rapid velocity and wider range
compared to cloud-to-ground lightning. The differences between the two types of cloud discharge also reflect some discrepancies
between the discharge characteristics.
Supported by National Nature Science Foundation of China (Grant No. 40475007) and Foundation of Northwest Normal University
(Grant No. NWNU-KJCXGC-03-21) 相似文献
12.
Spatiotemporal characteristics of positive cloud-to-ground lightning discharges and bidirectional leader of the lightning 总被引：4，自引：0，他引：4
Krehbiel Paul 《中国科学D辑(英文版)》2006,49(2):212-224
The negative CG lightning discharges neutralizing negative charges in cloud usually dominate for most of thunderstorms. However, a lot of positive CG light-ning discharges often occur in the disappearing stage of thunderstorms, in the stratiform region of mesoscale convective systems and some supercells producing hail and tornado. Because the positive CG lightning discharges produce larger current of the return stroke and neutralize more charges due to the continuing currents with longer las… 相似文献
13.
Radio frequency observations of cloud-to-ground lightning (CG) were made in 1999 in Guangdong Province with the broadband
lightning interferometer. In this paper, radiation source locations and electric field waveforms are analyzed for different
types of breakdown events, including the preliminary breakdown of in-cloud activities, the stepped leaders of initial strokes
to ground and activities during and following return strokes. It is shown that the structure and development of lightning
discharges and associated breakdown processes can be reconstructed by using this new type of lightning radiation source location
system. The detectable radiation of lightning was primarily produced by the negative breakdown process. The channel was concentrated
with few branches during the preliminary breakdown stage of CG lightning flashes. The radiation sources appeared generally
at the tip of the channel. During the late period of the stepped leader, the radiation sources were dispersed with branches
extended away from the main channel. The radiation sources were in a certain length segment of the channel and the altitude
of the segment descended along with the propagation of the leader to the ground. During the preliminary breakdown and the
stepped leader of initial strokes to the ground, a sequence of fast negative streamers were observed to start continually
from or farther away the lightning-initiated region and propagate along the developed leader channel, which may supply negative
charge that assisted the leader’s development. The progression speed of fast negative streamers was about ten times faster
than the average speed of lightning channel. 相似文献
14.
利用闪电宽带干涉仪系统对闪电的观测表明，地闪和云闪的云内闪电通道都存在双向发展的特征. 闪电在云中负电荷区域初始激发以后，在通道两端发生向不同方向同时发展的击穿过程. 这两种击穿过程均产生较强的辐射，且辐射频谱特征十分相似，表明云内闪电通道两端发生的击穿过程可能均为负击穿过程. 相应电场变化表明闪电通道双向发展期间伴随着负电荷的向上转移. 这一观测事实与Kasemir早期提出的闪电通道双向发展的概念有一定的差异. 相似文献
15.
Artificially triggered lightning and its characteristic discharge parameters in two severe thunderstorms 总被引：2，自引：0，他引：2
Qie XiuShu Zhang QiLin Zhou YunJun Feng GuiLi Zhang TingLong Yang Jing Kong XiangZhen Xiao QingFu Wu ShuJun 《中国科学D辑(英文版)》2007,50(8):1241-1250
The lightning-induced-damages in the mid-latitude regions are usually caused during severe thunder-storms. But the discharge parameters of natural lightning are difficult to be measured. Five lightning flashes have been artificially triggered with the rocket-wire technique during the passage of two severe thunderstorms. The discharge current and close electric field of return stroke in artificially triggered lightning have been obtained in microsecond time resolution by using current measuring systems and electric field change sensors. The results show that the five triggered lightning flashes include 1 to 10 return strokes, and the average return stroke current is 11.9 kA with a maximum of 21.0 kA and a mini-mum of 6.6 kA, similar to the subsequent return strokes in natural lightning. The half peak width of the current waveform is 39 μs, which is much larger than the usual result. The peak current of stroke Ip (kA) and the neutralized charge Q(C) has a relationship of Ip = 18.5Q0.65. The radiation field of return stroke is 5.9 kV·m-1 and 0.39 kV·m-1 at 60 m and 550 m, respectively. The radiation field decreases as r -1.119 with increase of horizontal distance r from the discharge channel. Based on the well-accepted transmission line model, the speed of return stroke is estimated to be about 1.4×108 m·s-1, with a variation range of (1.1―1.6)×108 m·s-1. Because of the similarities of the triggered lightning and natural lightning, the results in this article can be used in the protection design of natural lightning. 相似文献
16.
Bin Fan Ping Yuan Xuejuan Wang Yang Zhao Jianyong Cen Yanling Su 《中国科学:地球科学(英文版)》2018,61(8):1127-1135
Using the optical images of a cloud-to-ground lightning flash with multiple grounding points obtained by a highspeed video system in the Qinghai Province of China along with synchronous radiated electric field information, the propagation characteristic and the electric field change features of the leaders and the grounding behavior of discharge channels are analyzed.In addition, the two-dimensional velocity of the leader was estimated and its correlation with the time interval of the corresponding subsequent return stroke, and that with the peak current of return stroke are investigated. The results show that the average distance between the three obvious grounded points of the first return stroke channel is about 512.7 m, and the average time interval between the pulses of the corresponding electric field fast changes is 3.8 μs. Further, the average time interval between electric field pulses from the stepped leader is smaller than that of normal single grounding lightning. The observed lightning in our study has two main channels, namely the left and right channels. Based on our observations, it is clear that the dart leader comes close to the ground in case of the left channel after the first return stroke, but it fails to form a return stroke.However, the right channel exhibits a relatively rare phenomenon in that the subsequent return stroke R2 occurred about 2.1 ms after the dart leader arrived at the ground, which was unusually long; this phenomenon might be attributed to the strong discharge of the first return stroke and insufficient charge accumulation near the grounded point in a timely manner. The two-dimensional velocities for the stepped leader of the two main channels are about 1.23×105 and 1.16×105 m s-1, respectively. A sub-branch of stepped leader for the left channel fails to reach the ground and develops into an attempt leader eventually; this might be attributed to the fact that the main branch connects considerably many sub-branches, which leads to the instantaneous decline of the potential difference between the sub-branch and ground. Furthermore, it might also be because the propagation direction of this sub-branch is almost perpendicular to the atmospheric electric field direction, which is not conducive to charge transfer. The two-dimensional velocities for the dart leaders of five subsequent return strokes are all in the normal range, and they positively correlate with the peak current of the subsequent return stroke. 相似文献
17.
以中国静止气象卫星亮温资料为数据基础,使用小波变换和功率谱估计法研究2022年1月8日门源M6.9地震前的热辐射异常,并对祁连带中东段以往震例的热辐射异常作回溯性研究。门源6.9级地震的热辐射异常发展过程可分为3个阶段：初始演化阶段、增强持续阶段、减弱消失阶段。面积最大时强辐射区的面积约为8万km~2,地震发生在其西北部。相对功率谱峰值为平均值的17倍,地震发生在峰值后82天。大面积、高强度的热辐射状态持续时间长是此次异常的显著特点。祁连带中东段的几次地震前均出现过热辐射异常,其特征可为该区震情判定不断积累经验,以期形成可作为判定指标的区域震例库。 相似文献
18.
Vernon Cooray Mahbubur Rahman Vladimir Rakov 《Journal of Atmospheric and Solar》2009,71(17-18):1877-1889
Different approaches are used in estimating the global production of NOx by lightning flashes, including field measurements carried out during thunderstorm conditions, theoretical studies combining the physics and chemistry of the electrical discharges, and measurements of NOx yield in laboratory sparks with subsequent extrapolation to lightning. In the latter procedure, laboratory data are extrapolated to lightning using the energy as the scaling quantity. Further, in these studies only the return strokes are considered assuming that contributions from other processes such as leaders, continuing currents, M components, and K processes are negligible. In this paper, we argue that the use of energy as the scaling quantity and omission of all lightning processes other than return strokes are not justified. First, a theory which can be used to evaluate the NOx production by electrical discharges, if the current flowing in the discharge is known, is presented. The results obtained from theory are compared with the available experimental data and a reasonable agreement is found. Numerical experiments suggest that the NOx production efficiency of electrical discharges depends not only on the energy dissipated in the discharge, but also on the shape of current waveform. Thus, the current signature, can influence extrapolation of laboratory data to lightning flashes. Second, an estimation of the NOx yield per lightning flash is made by treating the lightning flash as a composite event consisting of several discharge processes. We show that the NOx production takes place mainly in slow discharge processes such as leaders, M components, and continuing currents, with return strokes contributing only a small fraction of the total NOx. The results also show that cloud flashes are as efficient as ground flashes in NOx generation. In estimating the global NOx production by lightning flashes the most influencing parameter is the length of the lightning discharge channel inside the cloud. For the total length of channels inside the cloud of a typical ground flash of about 45 km, we estimate that the global annual production of NOx is about 4 Tg(N). 相似文献
19.
Determination of horizontal and vertical design spectra based on ground motion records at Lali tunnel,Iran 
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下载免费PDF全文 Most acceleration diagrams show high levels of unpredictability, as a result, it is the best to avoid using diagrams of earthquake acceleration spectra, even if the diagrams recorded at the site in question. In order to design earthquake resistant structures, we, instead, suggest constructing a design spectrum using a set of spectra that have common characteristics to the recorded acceleration diagrams at a particular site and smoothing the associated data. In this study, we conducted a time history analysis and determined a design spectrum for the region near the Lali tunnel in Southwestern Iran. We selected 13 specific ground motion records from the rock site to construct the design spectrum. To process the data, we first applied a base-line correction and then calculated the signal-to-noise ratio (RSN) for each record. Next, we calculated the Fourier amplitude spectra of the acceleration pertaining to the signal window (1), and the Fourier amplitude spectra of the associated noise (2). After dividing each spectra by the square root of the selected window interval, they were divided by each other (1 divided by 2), in order to obtain the RSN ratio (filtering was also applied). In addition, all data were normalized to the peak ground acceleration (PGA). Next, the normalized vertical and horizontal responses and mean response spectrum (50%) and the mean plus-one standard deviation (84%) were calculated for all the selected ground motion records at 5% damping. Finally, the mean design spectrum and the mean plus-one standard deviation were plotted for the spectrums. The equation of the mean and the above-mean design spectrum at the Lali tunnel site are also provided, along with our observed conclusions. 相似文献