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21.
利用闪电作为辐射源来探测电离层D层是近年来国外学者研究的热点.本文基于江淮流域六站同步闪电观测站网,实现了一种利用闪电双极性窄脉冲事件（Narrow Bipolar Events,NBE）来探测电离层D层等效高度的方法.基于此方法,对两次分别发生在日出和日落阶段的雷暴分析结果显示,上述两个阶段D层反射高度变化特征呈现显著的不对称性：日出期间D层反射高度随时间线性降低速率为5.9 km/h;而日落期间D层反射高度随时间线性递增速率为8.6 km/h.综合日间太阳耀斑期间D层反射高度剧烈波动的观测事实,与日出、日落期间D层特征变化,结果表明太阳辐射电离中性大气分子的电子生成机制在日间D层电子密度变化中占主导地位.本文结果展现了利用NBE事件监测电离层D层变化特征的可行性,这一方法与基于地闪回击波形的D层探测方法结合在一起,有望把现有具有闪电事件定位和电磁波波形记录能力的闪电观测站网扩展为实时对电离层D层时空变化监测的网络. 相似文献
22.
闪电电场变化波形时域特征分析及放电类型识别 总被引：4，自引：0，他引：4
对闪电电场变化波形进行时域特征分析,研究闪电放电类型识别方法,是闪电探测系统研制工作的重要组成部分.利用闪电快电场变化资料,研究分析闪电波形的时域特征,分别统计负地闪回击和双极性窄脉冲波形的上升时间、下降时间、脉冲宽度等多个特征参数,得出负地闪回击波形上升时间平均值为2.9μs、下降时间平均值为89μs、脉冲宽度平均值为15.4μs,而双极性窄脉冲波形的上升时间平均值为1.7μs、下降时间平均值为2.1μs、脉冲宽度平均值为2.4μs.通过对闪电波形参数的统计分析,给出了不同放电过程的识别判据,实现了对地闪回击、双极性窄脉冲的自动识别,并利用实测数据进行了验证.结果表明,制定的波形识别判据对负地闪回击的识别效率可达到90%,对正地闪回击与双极性窄脉冲事件也有较高的识别率. 相似文献
23.
随着电子设备、计算机等大量的使用,全国气象信息中心的环境污染问题逐渐呈现出来.本文首次将可持续发展的概念引入到气象信息中心管理中.作为可持续发展的三大支柱,经济、环境、社会之间不可避免地存在冲突,双极模糊集对这类冲突信息具有强大的描述能力.考虑到可持续发展评价是一个多年的动态过程,本文提出了一种双极PROMETHEE可持续气象信息中心的动态评价方法.实例验证了新方法的有效性和可行性. 相似文献
24.
双极性窄脉冲事件（NBE）是一类特殊的大气放电现象,能产生强甚低频/低频（VLF/LF）和甚高频（VHF）辐射。为了探索NBE发生的气象环境和放电特性,选出重庆双频段闪电定位网络在一次雷暴过程中观测到的608次正极性NBE（简称正NBE）和82次负极性NBE（简称负NBE）,对比发生位置和辐射强度。结果表明:正NBE主要分布于7~15 km高度处,归一化到距离辐射源100 km处的VLF/LF电场变化峰值的平均值为13.4 V·m-1,平均VHF辐射功率为73.5 kW。负NBE主要发生在两个高度范围,72例负NBE分布于16~20 km高度,它们倾向于发生在30~35 dBZ回波顶高大于18 km的对流云顶及附近,其平均归一化VLF/LF电场变化峰值为42.7 V·m-1,平均VHF辐射功率为76.9 kW。10例负NBE分布于4~8 km高度,全部发生于对流核内部。其平均归一化的VLF/LF电场变化峰值为2.7 V·m-1,平均VHF辐射功率为18.2 kW。从统计结果看,在VLF/LF频段,上部负NBE的辐射强度普遍强于正NBE和下部负NBE;在VHF频段,上部负NBE的辐射强度与正NBE基本相当,大于下部负NBE;下部负NBE在两个频段的辐射通常弱于正NBE。 相似文献
25.
Chengwen WANG Songmei ZHANG.College of Earth Sciences Jilin University Changchun China.College of Resources Science & Technology Beijing Normal University Beijing China 《东北亚地学研究》2008,11(2):59-77
By reasearch on geographic distribution, nine genera in bipolar distribution are selected from Permian brachiopods. These taxa originated from middle-high latitude areas in the boreal realm, of which five genera were derived from Late Carboniferous, and other four genera originated from Permian. They were all in bipolar distribution during some different stages in Permian. Specific diversity for each genus was high in the boreal realm, whereas in the Gondwana realm was very low. Perdurability was long in the boreal realm, and short in the Gondwana realm. It was the time when these nine genera came to their maximum diversity that these genera appeared in the Gondwana and formed bipolar distribution; while they also migrated to the low latitude from high latitude. This shows very close relationship between several main cooling events in Permian and the migration of genera from the boreal realm to the Gondwana reahn through the Tethys. Therefore, the cooling events might be the main drive which caused these cold-water-type brachiopods migrated to the Gondwana realm and being bipolar distribution. In this process, the planula tolerance to warm water would be another important factor. 相似文献
26.
LATE‐GLACIAL GLACIER EVENTS IN SOUTHERNMOST SOUTH AMERICA: A BLEND OF ‘NORTHERN’ AND 'SOUTHERN’ HEMISPHERIC CLIMATIC SIGNALS? 总被引：2，自引：0，他引：2
D.E. SUGDEN M.J. BENTLEY C.J. FOGWILL N.R.J. HULTON R.D. McCULLOCH R.S. PURVES 《Geografiska Annaler: Series A, Physical Geography》2005,87(2):273-288
ABSTRACT. This paper examines new geomorphological, chronological and modelling data on glacier fluctuations in southernmost South America in latitudes 46–55°S during the last glacial–interglacial transition. Establishing leads and lags between the northern and southern hemispheres and between southern mid‐latitudes and Antarctica is key to an appreciation of the mechanisms and resilience of global climate. This is particularly important in the southern hemisphere where there is a paucity of empirical data. The overall structure of the last glacial cycle in Patagonia has a northern hemisphere signal. Glaciers reached or approached their Last Glacial Maxima on two or more occasions at 25–23 ka (calendar) and there was a third less extensive advance at 17.5 ka. Deglaciation occurred in two steps at 17.5 ka and at 11.4 ka. This structure is the same as that recognized in the northern hemisphere and taking place in spite of glacier advances occurring at a time of high southern hemisphere summer insolation and deglaciation at a time of decreasing summer insolation. The implication is that at orbital time scales the‘northern’ signal dominates any southern hemisphere signal. During deglaciation, at a millennial scale, the glacier fluctuations mirror an antiphase 'southern’ climatic signal as revealed in Antarctic ice cores. There is a glacier advance coincident with the Antarctic Cold Reversal at 15.3–12.2 ka. Furthermore, deglaciation begins in the middle of the Younger Dryas. The implication is that, during the last glacial–interglacial transition, southernmost South America was under the influence of sea surface temperatures, sea ice and southern westerlies responding to conditions in the 'southern’ Antarctic domain. Such asynchrony may reflect a situation whereby, during deglaciation, the world is more sensitized to fluctuations in the oceanic thermohaline circulation, perhaps related to the bipolar seesaw, than at orbital timescales. 相似文献
27.
卫星观测证实了磁尾等离子体团与亚暴活动的相关性,除了具有北-南双极特征的尾向传播等离子体团外,还发现地向传播等离子体团,它们表现为南-北双极中性片事件和南-北双极瓣区讯号. 资料分析表明:南-北双极讯号的出现几率远低于北-南双极讯号,并且南-北双极事件主要发生于行星际磁场北向和地磁宁静条件,它们往往与小的孤立的地磁亚暴相关. 本文根据地磁宁静时期(IMF Bz北向且By≥Bz)越尾电场Ey分量的分布特点,对地向传播等离子体团作模拟研究. 两类算例的数值结果展示了通量绳磁结构及具有复杂闭合磁力线位形的等离子体团的基本特征,上述特征与尾向传播的等离子体团类似,与IMP 8卫星关于地向传播南-北中性片事件的观测特征大致相符. 数值结果还展示了与Schindler示意图相类似的磁力线拓扑位形,在一定程度上为南-北事件出现几率低作出了解释;并且揭示了磁尾中性片内越尾磁场分量By对磁重联发展的抑制作用. 本文的模拟研究说明:无论磁尾处于活动时期(IMF Bz为南向),还是宁静时期(IMF Bz为北向且By≥Bz),磁场重联均是磁尾等离子体加速和加热的通用机制. 相似文献
28.
袖珍云闪是一类区别于常规闪电放电过程的特殊放电现象,能够同时产生极强的高频和低频辐射信号,其低频辐射信号在电离层与地面之间反射后能够在电场变化波形上形成电离层反射脉冲对.电离层反射信号与原信号的时间差包含着放电三维位置和电离层高度的信息,而借助于多站闪电探测网络的同步观测就能够反演这些信息.基于这一规律,本文发展了一种对袖珍云闪实现三维定位的新方法.这种方法不仅能够对大范围内的袖珍云闪实现准确的三维定位,同时还能够反演电离层的高度,是一种潜在的研究电离层相关性质的有效手段.通过将定位结果与雷达回波比较,证明这种方法具有较高的精度.利用这种方法,计算了5489例正极性袖珍云闪和1400例负极性袖珍云闪的放电高度,发现正极性袖珍云闪主要集中在7~14 km,而负极性袖珍云闪达到了15~18 km.负极性袖珍云闪的放电高度总体上与对流层顶高度相当,其数量相比于正极性袖珍云闪明显偏少,因此很可能产生于较为罕见的极旺盛的雷暴过程中. 相似文献
29.
C. J. Skinner M. Meixner M. J. Barlow K. Justtanont J. F. Arens J. G. Jernigan 《Astrophysics and Space Science》1995,224(1-2):383-386
We have obtained resolved IR images, at wavelengths from 1.2µm to 12.5µm, of a small sample of protoplanetary nebulae. The results suggest that all PPNe are axially, not spherically, symmetric, that spherical symmetry ends at the tip of the AGB, and that AGB evolution terminates with a burst of remarkably rapid, equatorially concentrated mass-loss. 相似文献
30.
The millennial‐scale asynchrony of Antarctic and Greenland climate records during the last glacial period implies that the global climate system acts as a bipolar see‐saw driven by either high‐latitudinal and/or near‐equatorial sea‐surface perturbations. Based on the results of recent modelling of generic Heinrich and Dansgaard–Oeschger scenarios, we discuss the possibility that oscillations of the deep‐ocean conveyor may have been sufficient to cause this bipolar see‐saw. The bipolar climate asynchrony in our scenarios is caused by the toggle between North Atlantic heat piracy and South Atlantic counter heat piracy. Ocean circulation has an enhanced sensitivity to the northern deep‐water source as the North Atlantic Deep Water (NADW) cannot enter the Southern Ocean at depths shallower than the bottom of the Drake Passage. Any shoaling of the NADW can, therefore, increase the northward incursion of Antarctic Bottom Water (AABW), and trigger an interhemispheric climate oscillation. As hundreds of years are required to warm the respective high latitudes, the observed climate lead and lags between the two hemispheres can be explained entirely by the variability of the meridional overturning and by the corresponding change in the oceanic heat transport. Accordingly, it is entirely feasible for the global climate to work like a pendulum, which theoretically could be controlled by pushing at either of the deep‐water sources. Our model scenarios suggest that it is entirely feasible for the bipolar climate see‐saw to be controlled solely by variations in NADW formation. Copyright © 2001 John Wiley & Sons, Ltd. 相似文献