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.     

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.     

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.     

Midlatitude seasonal behaviour of tides near the mesopause level

Wind measurements near the mesopause level were provided in Badary (Eastern Siberia, U.S.S.R.) by the Dl method using a low-frequency (200kHz) radio transmitter during 1976–1986. The seasonal variations of the wind are analyzed and compared with other midlatitude wind measurements as well as some theoretical predictions. It is shown that tidal parameters depend not only on latitude but on the longitude as well.     

A scintillation theory of the fading of HF waves returned from the F-region: receiver near transmitter

Scintillation theory is used to study the fading of HF radio waves returned from the ionospheric F-region to a receiver close to the transmitter. Estimates are made of

• 1.(i) the fluctuations of phase both for long term (∼ an hour) and for short term (∼ a fading correlation time),
• 2.(ii) the correlation distance,
• 3.(iii) the quasi-period of fading,
• 4.(iv) the angular divergence in the direction of arrival around the zenith and
• 5.(v) the correlation bandwidth.

The calculations are made as a function of wave frequency for two ionospheric penetration frequencies representative of high day-time values and low pre-sunrise values. Results are compared with observations of fading made with ionosondes over the past 40 years. Precise comparison is rendered impossible by omissions in the experimental data caused by lack of guidance from scintillation theory. Nevertheless, agreement is promising. When fading is deep but spread-F-region is not well-developed there is a slow modulation of the fading. This is what, for optical propagation in the troposphere, is called twinkling. The slow fluctuations observed by Bramley and Ross in the HF band constitute ionospheric twinkling. Calculated quasi-periods of twinkling range from about an hour down to about a couple of minutes, while calculated quasi-periods of fading range from about a couple of minutes down to about a tenth of a second.     

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.     

Simultaneous observations of the enhanced plasma line and of the reflected HF wave at Arecibo

A suitably devised pulsing sequence of the powerful HF transmissions radiated towards the ionosphere below the penetration frequency made it possible to separate the attenuation of the reflected HF wave due to thermal and to ponderomotive type parametric instabilities. The separation was possible on account of the different growth times of the thermal and ponderomotive type parametric instabilities. At the same time the power in the 430 MHz enhanced plasma line was recorded.The results show that previously accepted explanations of the overshoot in the 430 MHz enhanced plasma line for 5.3 MHz HF transmissions are invalid. A strong overshoot was observed but the attenuation of the powerful HF wave was too small to be observed. For 3.175 MHz HF transmissions substantial attenuation was observed on both time scales.     

Avian resources at a Mexican site at the time of the Spanish Conquest

The time of the Spanish Conquest in America saw a major biological interchange caused by human action. In the native people it was expressed by major changes in the use of animals, due to the introduction of domestic European fauna. This theme is discussed here based on a review of ethnohistorical sources and a small body of recent archaeological evidence. An analysis is presented of the use of birds at a Mexican settlement inhabited in the sixteenth century at the time of Spanish contact. The bird remains, 456 fragments, are from the site of El Japon, southeast of Mexico City. The main avian resources were domestic fowl, Gallus gallus, turkey, Meleagris gallopavo, and four species of ducks. The exploitation of scrub jay, Apheolocoura coerulescens is recorded for the first time in Mexican archaeo-ornithology. The study confirms ethnohistorical information about the introduction of the domestic fowl, but also shows that native resources were more widely used than is known from the chronicles of the sixteenth century. © 1997 John Wiley & Sons, Ltd.     

清代东北地区布特哈八旗建立时间考辨

清代在东北边疆鄂温克、鄂伦春、达斡尔等少数民族聚居地区,设立布特哈八旗进行管理,实行这种制度对这些民族的历史发展产生了重要影响。关于布特哈八旗建立的时间,学界看法不一,本文对此问题略作探讨。     

试述明代南京守备的创设时间及首任内守备

明代留都南京设立内外守备、参赞机务等官员负责护卫留都安全,其中内守备设立最早,时间在永乐二十二年八月,外守备随即设立于次月。首任内守备应为王景弘（又名王贵通）,而非郑和。     

Set-up, optimization and first set of samples at the radiocarbon laboratory in Lebanon

A new radiocarbon laboratory has been established recently at the Lebanese Atomic Energy Commission. This laboratory consists of benzene synthesis line and a low background liquid scintillation counter, Tri-Carb 3180 TR/SL for measurements with Bismuth Germanate (BGO) guard detector. The effectiveness of the benzene line was tested firstly by preparing benzene from a wood sample after carbide and acetylene receiving. Normalization and standardization of the liquid scintillation counter was carried out, as well as the Factor of Merit (E2/B) was determined for three different counting regions. To assure accuracy and reliability of results, reference materials were used. Based on z-score and u-score evaluation, as well as Student’s t-test, acceptable data were obtained from travertine and wood samples available through the International Atomic Energy Agency (IAEA-C2 and IAEA-C5), and humic acid (U) and murex shell (R) from the Fifth International Radiocarbon Intercomparison (VIRI). After that, a preliminary study was done, which is the base for future research in order to assess the anthropogenic impact and degree of environmental pollution in terms of radiocarbon isotope ratio (Δ¹⁴C) deduced from the Percent Modern Carbon or PMC. This work represents the results of four reference materials and those of five green grass samples. The Δ¹⁴C of green grass samples collected from two different clean zones were found to be 50‰ and 52‰, while the values of those collected from different polluted zones were 23‰, 7‰ and 15‰.     

Magnetic observations at the time of the 23 October 1976 solar eclipse in Australia

The solar eclipse of 23 October 1976 passed across south-east Australia in the local solar afternoon. This paper records the magnetic observations of a line of ten temporary stations stretching from a region of fifty percent obscuration to the path of totality. Magnetic conditions at the time were mildly disturbed. Analyses of the data have sought an eclipse effect in the basic quiet daily variation, and also in the disturbance variations. However, no eclipse effect in the primary ionospheric currents has been clearly distinguished above spatial uneveness, due to local differential induction, in the induced secondary currents flowing in the earth.     

Music in worship and recreation at Little Gidding in the time of the Ferrars

This paper investigates the use of music in worship and recreation at Little Gidding in the first half of the Seventeenth Century. The major focus is the relatively short period from the establishment of the Ferrar family in the Manor House at Little Gidding in 1626 until the death of Nicholas Ferrar in December 1637. Worship encompasses both the formal services in the churches at Little Gidding and Steeple Gidding, and the informal devotions of the Ferrar family in the Manor House. Recreation is conceived broadly, to embrace both the proceedings of the Little Academy and the “night watches”. In each case, religion and piety are central to the activities. The study begins by investigating the Ferrars’ musical education and competence; it then moves on to music in worship, followed by music in recreation. A section on the organs at Little Gidding and their possible fate is followed by conclusions.     

秦岭-淮河南沿线地区宋代墓葬的初步研究

目前秦岭一淮河南沿线地区发现的宋代墓葬已积累了一定的数量,从这些墓葬所反映的特点来看,受到了南方地区和中原地区的共同影响.我们从墓葬形制和随葬品的特征出发,总结了这些墓葬的特点和阶段性特征,并对这些现象产生的原因进行了初步的探讨.