A wave guide model of lightning currents

In this paper, a lightning channel is simulated by a vertical wire of finite length and of moderate electric conductivity. At low frequencies, such a wire behaves like a resonant wave guide cavity in which only discrete resonant wave modes can be generated. The theory of resonant waves in a wire of finite diameter is outlined and applied to the return stroke with electric contact to the earth and to intracloud K-strokes without electric contact to the earth. Two types of current wave forms exist: aperiodic waves of the Bruce-Golde type and damped oscillations. The configurations of the electric charge density and the electric current in the wire are presented for the various wave modes as functions of height and time. From the observations of lightning current and of sferic wave forms, it is apparent that the first mode dominates, and that both types of wave forms can be identified. From these wave forms, the channel parameters-length and diameter can be derived. For the higher order modes, the resonance model loses its validity and freely propagating waves are expected during the whole lightning flash. These waves contribute to the observed continuous spectrum. The skin effect becomes important increasing the effective resistance of the wire with frequency. Since these waves interfere destructively, they do not contribute significantly to an effective charge transport.     

Current and velocity of the return stroke lightning

An expression for the current flowing through the return stroke channel is derived from the actual flow of charge across the tip of the channel. From the current model a double exponential velocity expression is obtained. The consequence of this double exponential velocity expression for the spectrum of atmospherics is discussed. The variation of current and velocity with increasing length of channel is also discussed and appropriate expressions for the same are obtained.     

Some remarks about a ball lightning model

Two criticisms of a model for explaining the nature of ball lightning are discussed. It is shown why these criticisms are groundless. Furthermore, by considering the topics in question in a wider context, the reliability of the model is further substantiated. Comparisons between model expectations and ball lightning reports, including laboratory ball lightning, are considered and again the model turns out to be in agreement with observations.     

Plasma wave evidence for lightning on Venus

Plasma wave data from the Pioneer Venus Orbiter provide the largest body of data cited as evidence for lightning on Venus. These data are also the most controversial, mainly because of the ambiguity in mode identification due to limited spectral information. We review some of the more recent studies of the plasma wave data at Venus, and we demonstrate that the characteristics of the 100 Hz waves are consistent with whistler-mode waves propagating vertically from below the ionosphere. We further show that in situ instabilities are too weak to generate whistler-mode waves, mainly because the thermal pressure is comparable with the magnetic field pressure in the ionosphere of Venus. The lower hybrid drift instability has also been suggested as an alternative source for the 100 Hz waves. However, the wave properties are more consistent with whistler-mode propagation; the lower hybrid drift instability requires very short gradient scale lengths to overcome damping due to collisions. We also note that an apparent association between Langmuir probe anomalies and 100 Hz waves is much lower than previously reported, once we apply a consistent intensity threshold for identifying wave bursts. The lightning hypothesis remains the most probable explanation of the plasma waves detected at low altitudes in the nightside ionosphere of Venus.     

A possible way to trigger lightning using a laser

To study the possibility of triggering lightning with a laser plasma, laboratory laser-induced discharge experiments have been carried out and the following results were obtained. Both long straight and zigzag laser induced discharges between rod-rod electrodes were realized and the effective guiding effect of laser channels for electrical discharges was confirmed. With plane-plane electrode configuration, the investigation concerning the necessary condition for initiating and guiding a streamer reveals that the necessary electric field for initiating a streamer with a laser plasma depends closely on the absorbed energy used to produce laser plasma channels, the minimum electric field is about 200 kV/m, and that the necessary electric field for guiding a streamer by a laser plasma is lower than that for initiating a streamer and the minimum electric field is about 170 kV/m.We propose to use the local electric field near the top of a grounded tower as the necessary field for a laser-produced channel to trigger an upward leader and have proved that this is feasible.     

Some effects in the middle atmosphere due to lightning

A brief review is given of some of the electrodynamic responses of the middle atmosphere to lightning. Attention is focused on the precipitation of energetic electrons from the magnetosphere, due to whistler mode electromagnetic waves. The secondary ionisation and bremsstrahlung radiation created, and some of the ways in which such effects can be detected, are also considered. Finally, the possibilities of positive feedback mechanisms operating between the atmosphere and the magnetosphere are investigated.     

非物质文化遗产 骊山吹歌 乡土之音在高山 冬日里的喇叭队

中国长城是世界上最长的室外文物,历史悠久,工程雄伟。1987年被联合国教科文组织列入世界文化遗产名录,是各国人民始终公认并向往的世界奇迹、人类遗产。长城脚下的"吹歌",出现在明朝戚继光所镇守的天马山下骊城一带(秦皇岛抚宁县域),2006年,被列入河北省和国家非物质文化遗产保护名录。因当地"吹歌"的普及,骊城被河北省文化厅命名为"河北省民间文化艺术之乡"。由此,这里吹喇叭的庄稼汉子,经常被全国各地民间艺术活动组委会邀请,从而走南闯北,有了别样出游的脚步;各种人群也慕名拜访长城脚下的吹歌之乡,有了别样天地的游历。2007年11月16日,本刊记者和中央电视台7套节目的《乡土》栏目记者一起,做了一次新年前的寻访之旅——爬骊城的界岭口长城听吹歌,领略那方水土上红日子、白日子都不可少的乡土之音。     

Wave form and spectral distribution of the electromagnetic field of lightning currents

In a resonant wave guide model of lightning currents, two impulse type standing waves can exist: aperiodic waves of the Bruce-Golde form (type 1), and damped oscillations (type 2). The electromagnetic waves generated by these two types of lightning currents are calculated for various distances and compared with observations. It is shown that the measured wave forms of sferics at distances smaller than about 300 km of return strokes (R strokes) as well as of intracloud strokes (K strokes) are generated mainly by type 2 lightning currents. The channel parameters like channel length and channel diameter derived from the observed sferics are 19 km and 4.6 cm, respectively, for the average R stroke, and 4 km and 1.6 cm for typical K strokes. The large values of the lengths probably correspond to the real lengths of oblique and tortuous channels, rather than to their vertical elevation. The finite electric conductivity of the earth modifies the high frequency component of the wave forms. With decreasing conductivity and/or increasing distance, the rise times of the radiation component to its first maximum increases and the maximum amplitude decreases.Typical rise times for R-strokes are about 3 μs consistent with the observations if the electric conductivity of the earth is of the order of 10⁻³ S/m. The spectral functions of the wave forms are also calculated. The spectral amplitude of the average type 2 R-stroke has its maximum near 4 kHz, and that of the type 2 K-stroke maximizes near 35 kHz. Within the high frequency region at frequencies greater than about 300 kHz. the spectral amplitudes decay proportional to the reciprocal third power of the frequency. The radiation component in the far field contains 7% (16%) of the total electromagnetic energy of type 2 R (K) strokes.     

酷寒里的暖调

<正>冬季,天寒地冻,草木凋零。夏日的蝉鸣热噪树影婆娑似乎遥远了一个世纪,变得不真实,仿佛从未有过一样。曾经的清风柔月,夏花绚烂都是真的吗?一些人变得郁郁寡欢,百无聊赖,精力也明显衰退,据专家们称,这种情形叫"冬季抑郁症"。     

Association of whistlers with lightning discharges on the Earth and on Jupiter

The association between whistlers and lightning discharges has been reviewed on the basis of terrestrial ionospheric satellite observations of VLF radio noise. Evidence indicating that the observed low-latitude radio noise is associated with thunderstorms includes (1) amplitude distribution and noise properties, (2) geographical location, (3) diurnal variation in activity, and (4) diurnal variation of frequency spectrum. Corresponding studies on the propagation of sferics in the ionosphere and the excitation of whistlers recently carried out for Jupiter are presented here and compared with the terrestrial studies.     

Temporal variations of the global lightning activity deduced from the Schumann resonance data

Temporal variations of the global lightning activity were deduced from long-term Schumann resonance (SR) continuous records. The intensities of the horizontal magnetic field component in the vicinity of the first, second, and third SR modes were monitored at Tottori observatory (35.5°N, 134.33°E) from 1968. Variations of the effective source-observer distance were estimated using the ratios of the intensities of individual modes. This allowed us to obtain average diurnal variations of the global lightning activity for each month over a one-year period. The results show that the distances estimated between the field-site and the effective source are very stable, while the temporal changes of the fields and the global lightning intensity derived demonstrate substantial variability.     

The lightning HF radiation at 3 MHz during leader and return stroke processes

Simultaneous recordings of the broadband electric field and HF radiation at 3 MHz were obtained at times before and after the onset of first and subsequent lightning strokes. Data are presented for several hundred negative ground flashes observed in Sri Lanka within a range of 40 km over the land and sea. The stepped leader gave rise to strong 3 MHz radiation, but the peak amplitude of the radiation was less than that of the return stroke. In the return stroke phase, 3 MHz radiation was strongest at the beginning of the first return stroke and gradually decayed completely. The mean duration of the 3 MHz continua of 346 first strokes was 190 μs (S.D. = 69 μs). In about 99% of the cases 3 MHz radiation in the return stroke phase was accompanied by a burst of multitudinous, fine oscillatory pulses on the broadband electric field. Subsequent strokes, in general, had no 3 MHz radiation in their return stroke phases.     

闪回2007,大约在冬季 摄影人——特别关注篇

旅游不是道路的延伸,而是心灵的铺陈。因此,摄影人(权且归群为"摄族")也最顺应当今旅游的目的取向:我们已经不再乐道去过什么地方,而是追求在什么地方体验了什么。摄族的涉足从来不浅尝辄止;摄族向生命的原乡、自然的深处走去,选择了养心。     

冬日暖暖的布绒那

有这么一位活佛,文革期间还俗,结婚、生子,文革后又重新当上了活佛。他在废墟上重建了布绒那寺,收养孤寡老人、孤儿,对朋友仗义得更像一个大哥。朋友都喜欢去他那里,他的家被朋友们称为“港湾”。     

基于事故树的布达拉宫雷击火灾风险分析与保护

布达拉宫自兴建以来曾遭受多次不同程度雷击,一旦雷击引发火灾会造成不可挽回的损失,因此需要进行科学合理的雷击火灾分析以有效指导布达拉宫减灾工作。对于布达拉宫雷电可能引起火灾的风险,建立布达拉宫雷击火灾事故树,综合考虑布达拉宫因雷电引发火灾事件发生的可能过程、可能途径。最后对雷击火灾事故树最小割集、最小径集、基本事件的结果重要度进行比较,同时分析布达拉宫地区雷电活动规律。分析结果表明:布达拉宫雷击火灾事故树一共有22个基本事件,有308种可能导致布达拉宫因雷击引起火灾事件发生的途径。布达拉宫雷击火灾防护是一项复杂工程。研究表明,最便于采取的防护措施是加强其雷电防御能力,如清除引雷隐患、安装电涌保护器、进行等电位连接等。     

塔尔寺古建筑的雷电环境分析与防护措施

青海塔尔寺具有很高的佛教历史和文物价值,但在2011年8月30日由于雷电波侵入,造成了塔尔寺的时轮坛城和大吉哇殿内的消防、安防及低压配电系统部分设备遭雷击损坏,也严重威胁到僧侣、游客的安全。因此,对塔尔寺古建筑实施雷电防护已是非常必要和十分紧迫。为此,在分析塔尔寺所在的地理环境、气候特点、雷暴特征、雷击风险评估结果等基础上,提出了对塔尔寺古建筑采取内部防护和外部防护相结合的综合防护措施:外部防护采用通过在塔尔寺雷暴路径上安装一定高度的避雷针来提前接闪拦截,再由建筑物天面安装的避雷带进行二次接闪,从而有效预防和减少塔尔寺建筑物遭受直接雷击。内部防雷采用屏蔽、合理布线、等电位连接、电源和其他进出建筑物的线路上安装电涌保护器等方法,预防和减少感应雷、雷电波侵入造成的危害。事实表明,避雷措施是可行的,能预防建筑物、人员免受雷击。对于与塔尔寺有类似环境的古建筑的防雷电有参考价值。     

Temporal behaviour of lightning HF radiation at 3 MHz near the time of first return strokes

Simultaneous recordings of the electric field and high frequency emissions (HF) at 3 MHz at times close to the first return stroke are presented. It is shown that there is no time delay between the beginning of the return stroke electric field and the build up of the HF. The delay observed in previous studies may be due to propagation effects. The results in turn suggest that the first return stroke from the very beginning is a strong source of HF at 3 MHz.     

大画幅摄影家刘玉丛 黄山冬日,诗意童话

<正>听摄友说,春日的黄山是一首诗;夏日的黄山是一支歌;秋日的黄山是一阕词,而冬日的黄山则是一篇梦幻般的诗意童话。2012年的腊冬里,寻梦般地,我踏上了去黄山的路。     

Scintillation at high latitudes during winter magnetic storms

Scintillation observations are described which were made at Kiruna in northern Sweden during three magnetic storm periods in the winter of 1984–1985. The results were obtained using transmissions from the multisatellite NNSS system, so that it has been possible to chart the development of scintillation activity over some 20° of geomagnetic latitude as a function of time for several days throughout each storm. A region of strong scintillation at the highest latitudes near magnetic noon is a common feature on all but the quietest days. This feature, probably associated with soft particle precipitation into the cusp, shows an abrupt boundary which moves equatorwards as the disturbance develops. In the magnetic midnight sector two latitudinally separate zones of scintillation are found, patchy at high latitudes although more sustained in the auroral zone. An absence of auroral scintillations around midnight UT can be followed by prolonged intense scintillation activity at auroral latitudes during the early morning hours on some disturbed days.     

Recent advances in the study of the D-region winter anomaly

D-region work as concerns the winter anomaly of electron density is screened for the period 1974–78. The following topics are dealt with: electron density distribution; ion production processes; neutral atmosphere effects by trace constituents, temperature and transports; ion composition and chemistry; coupling between atmospheric/ionospheric layers. A summary is given which might be read first, and which leads to some aspects of future work.