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.     

On the polarity and continuing currents in unusually large lightning flashes deduced from ELF events

An analysis of ELF events has enabled the magnitude and duration of the continuing currents in 274 unusually large lightning flashes to be estimated. An exponential decay model of the variation of the current moment of the source lightning stroke with time was fitted to the measured spectra using an optimisation algorithm. Of the events analysed, 212 were of positive polarity (i.e. the initial polarity of the electric field was positive) and 62 were negative. The average magnitude of the peak current moment for positive events was 5.1 × 10⁷ Am with a standard deviation of 3.2 × 10⁷ Am while that for negative events was 2.9 × 10⁷ Am with a standard deviation of 0.6 × 10⁷ Am. The average time constant T of our data set is 32 ms with a standard deviation of 6 ms for positive events and 26 ms with a standard deviation of 5 ms for negative events. Positive events are therefore associated with somewhat larger and more variable current moments and slightly longer continuing currents. We believe that these positive events are most likely to be produced by positive cloud to ground lightning.     

Three dimensional ionospheric currents and field aligned currents generated by asymmetrical dynamo action in the ionosphere

Three dimensional ionospheric currents and field aligned currents generated by asymmetrical ionospheric dynamo are calculated self-consistently, using the assumption of infinite parallel conductivity. Tidal winds of (1, −2) mode, which are generally accepted as a main cause of Sq fields, are adopted as a wind model. Variation in universal time (UT) is examined by considering the discordance between conductivity and wind distribution, which are assumed to follow the geographic coordinate system, and geomagnetic dipole field. Observed UT variation of Sq current system is partly reproduced by our calculation. Calculation for solstice condition is performed by shifting conductivity distribution by 23.5° in latitude. Height integrated westward currents are much smaller in the winter hemisphere than in the summer hemisphere, though eastward currents are not so different in both hemispheres. This unbalance is compensated by the field aligned currents mainly from summer to winter hemisphere in the morning and vice versa in the afternoon. In both above asymmetric cases, structure of the equatorial electrojet is almost symmetric with respect to the equator. Total field aligned currents are rather large and comparable to currents in the ionosphere.     

Temporal and spatial distribution of the spectral components of foF2

A spectral analysis of almost all available monthly median of the maximum plasmafrequency in the F-region (foF2) was performed. Some evidence for a significant tidal influence on the diurnal and semidiurnal variation has been found. The declination effect (Eyfrig, 1963) appears in our spectral presentation as a dependence of the degree of the seasonal variation and of the phase of the 24 hour period on the magnetic declination. The most peculiar phenomenon is the different variation of the annual component in North America and Eurasia with the sunspot number. There are several indications that the variation of (foF2) is also influenced by the variation of the gravitational potential. Some other results are presented which are believed to be related to dynamic processes in the F-region.     

Study of the annual changes of global lightning distribution and frequency variations of the first Schumann resonance mode

From the yearly averaged diurnal variations of the first Schumann resonance frequency, corresponding changes in the area covered by global lightning were calculated and then compared with optical observations made by satellite 11 years later. The data observed are characterized by the high cross-correlation coefficient. The conclusion is that Schumann resonance frequency variations are an indicator of the thunderstorm distribution over the globe.     

Simulation of ionospheric currents and geomagnetic field variations of Sq for different solar activity

Variations of ionospheric Sq electric currents and fields caused by changes in electric conductivity due to changes in solar activity are studied using the International Reference Ionosphere (IRI) model. Calculations are made for R (sunspot number) = 35 and 200 on the assumption of constant (1, −2)mode tidal winds. It is shown that electric fields grow when solar activity is high, because the ratio of the conductivity in the F-region to that in the E-region increases. Currents in the F-region become stronger than those in the E-region, and nocturnal currents are not negligible when solar activity becomes high. F-region currents also play an important role in the westward currents on the high latitude side of the current vortex. The calculated geomagneticH component at the equator has a depression around 1600 LT for R = 35, while it decreases smoothly from 1100 LT to 1900 LT for R = 200. This difference is consistent with the observed geomagnetic field variation. The ratio of total Sq currents obtained by our simulation is about 3.5, which is a little larger than is found in the observed results.     

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.     

Production of electromagnetic field disturbances due to the interaction between acoustic gravity waves and the ionospheric plasma

The problem of electromagnetic field disturbances produced by the interaction between winds of acoustic gravity waves (AGW) origin and the ionospheric plasma has been considered. It is shown that, when not allowing the electrostatic approach, electromagnetic field disturbances represent shear Alfvén and compressional modes modified by ionospheric Pedersen and Hall conductivities. It is further shown that the quasielectrostatic Alfvén type disturbances give the main contribution to electric field perturbations. Magnetic field perturbations due to Alfvén and compressional modes have the same order of magnitude. Two numerical models for simulation of the problem under consideration have been developed. The first model is intended for the simulation of Alfvén type disturbance production and transmission into the magnetosphere, taking into account the dipole geometry of the geomagnetic field, but a mutual transformation of Alfvén and compressional modes is ignored. The second model is constructed for the simulation of both electromagnetic field disturbance production and their mutual transformation in the ionosphere. The results of numerical simulations with these models show that there is an opportunity for AGW activity monitoring in the lower thermosphere by ground-and satellite-based recordings of magnetic and electric field variations.     

Analytical modelling of the electric field distribution in the high-latitude ionosphere

An analytical approach is implemented for self-consistent modelling of the high-latitude convection electric field. Input parameters are determined as distributions of field-aligned currents and height-integrated conductivity. The high-latitude ionosphere is approximated with an arbitrary number (N) of concentric rings. The height-integrated conductivity (∑) is independent of co-latitude within any ring, but depends on the longitude ~ sin λ. The field-aligned currents flow only along the boundaries of each ring and are presented by Fourier series in longitude. The analytical solution for the potential φ as a function of longitude is also presented as a Fourier series. An analytical solution is obtained for the potential dependencies on co-latitude. For the extreme case, when the integrated conductivity does not depend on longitude, this solution coincides with the analytical results, obtained by other authors. Based on this solution, the potential distribution in the high-latitude ionosphere, an example with N = 5 is shown, the values of conductivity and field-aligned currents being similar to those values used by other authors.     

Effect of the electric field on the equatorial ionospheric plasma distribution

It is known that on a counter electrojet day the noontime electron density at the equator shows enhanced values with no bite-out. The consequences of the absence of the normal equatorial electrojet on the electron density distribution at the equatorial station Kodaikanal (dip latitude 1.4°N, long. 77.5°E) and at an anomaly crest location Ahmedabad (dip latitude 18°N, long. 73°E) are discussed for a strong electrojet (SEJ) day and a counter electrojet (CEJ) day. The electron density distribution with height for a pair of SEJ and CEJ days at the two equatorial stations Kodaikanal and Huancayo (dip latitude 1°N, long. 75°W) are studied. The F-region peak height, hm and the semi-thickness parameter ym on the SEJ day followed a similar variation pattern. On the CEJ days ym exhibited a substantially low and mostly flattened daytime variation compared to the peaked values on the SEJ day. An attempt is made to interpret these differences in terms of the changes in the vertical drift pattern resulting from the E × B drift of plasma at the equator and the varying recombination rate β, which is also a height dependent and a local time dependent parameter.     

乾陵无字碑温度场分布规律研究

由于长期裸露在自然界中,无字碑表面风化严重,温度是影响无字碑风化的主要因素之一。为了探究无字碑温度场的分布规律,在传热学基本原理的基础上建立了无字碑三维分析模型,基于Comsol Multiphysics仿真软件对无字碑在太阳辐射下的温度场进行了计算。结果表明无字碑温度由表面到内部的变化趋势呈抛物线型,越靠近无字碑中心处日温度变化量越小。随着太阳方位角和高度角的改变,无字碑4个表面温度分布极不均匀,在水平方向和竖直方向均出现了温度梯度,形成了较大温差。该研究结果可为无字碑的保护工作提供科学有效的依据。     

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.     

多维视角下的近代安徽族田分布

本文从祠堂数量、捐献族田人数以及土改调查的族田量分别对近代安徽族田的分布状况进行考察,在综合比较的基础上,勾画出近代安徽族田分布呈现自南部徽州山区向淮北平原地区递减的总体态势及其起伏.     

The impact of gaps and spectral methods on the spectral slope of the middle atmospheric wind

The spectral slope of the middle atmospheric wind is an important index of the gravity wave and turbulence processes. Gaps exist in MF radar spaced-antenna winds data because significance criteria are built into the analysis. These cause a smearing of the spectrum and seriously modify the slope, as well as affect the absolute power at high frequencies. A comparison between sites with different gap rates must account for this. Different methods of dealing with these gaps are tested in this paper. The periodogram (with linear interpolation across gaps), the correlogram, and the Lomb-Scargle analyses are compared on synthetic data with known slope, and also with some of the best measured data (less than 20% gaps), both with added gaps to a maximum of 50%. The periodogram is seen to be the best choice. Parallel calculations on real data and synthetic data with the real gaps inserted are used to compare 1992 summer and winter spectral slopes from the Saskatoon MF radar. The latter are also compared with those of winter spectra from the two CNSR (Canadian Network for Space Research) radars which, with Saskatoon, form a ∼ 500 km array. A similar process is used to compare the seasonal variation of absolute power (10–100 min) at the three sites.     

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 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.     

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。     

Three-dimensional ionospheric currents and fields generated by the atmospheric global circuit current

Three-dimensional ionospheric currents and fields generated by atmospheric global circuit currents, using the distribution of air-Earth currents as a lower boundary conditions of the ionosphere, have been studied. The air-Earth currents are obtained taking geomagnetic and orographic effects into account, under the assumption of an ionosphere with infinite conductivity. Three dimensional ionospheric currents due to thunderstorm sources are calculated, considering the conductivity distribution in the ionosphere and the configuration of the magnetic field. The calculated potential difference in the ionosphere is 55 V and according to our model the horizontal electric field is too weak to affect the ionosphere and magnetosphere significantly. Horizontal currents are not distributed uniformly, but preferably in the day-side hemisphere and especially in the equatorial region, and vertical currents and fields do not simply decrease with altitude near the equator because of anisotropy and nonuniformity in the conductivity.