The mid-latitude trough in the electron concentration of the ionospheric F-layer: a review of observations and modelling

Experimental observations and theoretical modelling of the terrestrial mid-latitude trough are reviewed. The mid-latitude trough is considered as an F-layer phenomenon, and its relationships to the lightion trough in the topside ionosphere and to the plasmapause are discussed. The observed morphology of the mid-latitude trough is summarised. Recent evidence on plasma temperatures in the trough is examined. The physical processes that may be important in the trough region are listed. Large-scale computational models that include some of those processes are described and the results compared with observations. Deficiencies in the models and possible future developments are mentioned.     

Effects of composition and fountain effect on the annual variation of the day-time F-layer at low latitudes

The annual variation of the daytime F2-layer peak electron density (NmF2) is studied at two low latitude stations, Okinawa and Tahiti (geomagnetic latitudes ± 15°) for the sunspot maximum years 1979–1981. Observed values are compared with those calculated using the MSIS model and a simplified version of the continuity equation for day-time equilibrium conditions. Summer-winter differences imply an intensification of the fountain effect on the winter side of the equator at the expense of the summer side. This could be explained by a summer to winter neutral wind. Semi-annual variations, however, appear to be mainly due to changes in neutral composition.     

Internal structure of the equatorial ionospheric dynamo

Using the Sq current profiles measured with rocket born magnetometer, off the coast of Peru, by Daviset al. (J. geophys. Res. 72, 1845) comparison is made between measured and calculated profiles near noon on geomagnetic dip equator, and a mismatch is pointed out in the height pattern of Sq current. Theory is worked out to determine the eastward electric field (E_y) with which computed j_y (eastward current density) coincides with the observed one. It is found that the neutral wind plays very important rôle in keeping E_y height-independent. E_y is found to be about 0.6 mVm⁻¹, ranging from 0.5 to 0.7 mVm⁻¹ in some cases. Flow of meridional current is obtained and its effect on jet current construction is discussed.     

六朝武昌城试掘简报

六朝武昌城位于湖北省鄂州市区中部,长江南岸。2000年,为配合古城遗址保护规划的实施,我们对古城遗址的南城垣进行了首次发掘,同时发掘清理北宋墓葬10座,六朝早期古水井1座。通过此次发掘,弄清了城墙的结构和建筑方法。墓葬中出土了陶瓷器、铜器、银器和铜钱30余件(枚);古水井中出土遗物丰富,以陶瓷器为主,数量达100多件。古墓葬和古水井的发现,为了解研究六朝武昌城的发展历史,提供了新的实物资料。     

Travelling ionospheric disturbances and the effectiveness of powerful HF transmitters in ionospheric modification and radio location of the Moon

Using ray tracing we investigate, on a qualitative level and in the linear approximation, the effects of medium-scale travelling ionospheric disturbances (MS TIDs) arising when powerful HF radio transmitters are operated in conjunction with antenna arrays designed for ionospheric modification (heating) and for radio location of the Moon. It is shown that the HF radio wave focusing effect, arising during the movement of the MS TIDs, can give rise to a strong inhomogeneous and nonstationary modulation of the space-time distribution of the field intensity of a powerful radio transmitter both at heights near the reflection region (in heating experiments) and at the exit from the ionosphere (in radio location of the Moon). The excess of intensity over an unperturbed value for typical parameters of MS TIDs in experiments on ionospheric modification can reach values of hundreds of percent: a ‘spot’ of increased intensity of the wave field can have the size of about 1–10 km, and can move with a velocity close to the MS TID phase velocity.In the case of lunar radio location, the inhomogeneity and nonstationarity of the wave field intensity distribution at the exit from the ionosphere substantially complicates the evaluation of the corresponding distribution on the Moon's surface and the interpretation of the Moon-reflected radio signal characteristics.     

Distributions of the irregularities which produce ionospheric scintillations

The distribution of nighttime irregularities which produce satellite scintillation has been examined for a midlatitude location using a large array of receivers. The irregularities are aligned along the earth's magnetic field and appear to extend from top to bottom of the F-region, being preferentially observed near the F-region ionization peak where they produce the strongest scintillations. A new method of mapping the horizontal distribution shows patches of various shapes and sizes but with no systematic structure.     

Estimation of the true ionospheric height profile,with a continuous gradient,from oblique sounding data

A technique to calculate the true height ionospheric profile from multifrequency oblique soundings is proposed. In the classic isotropic statement of the problem, it avoids a discontinuity in the gradient of electron density with height at nodal points and. as shown in test examples, it considerably increases the accuracy of the reconstructed profile as compared with well known, currently employed methods. The influence of the geomagnetic field is taken into account in the technique by constructing the equivalent isotropic ionogram. Both numerical and experimental results are presented and discussed.     

Deconvolution of ionospheric parameters in the F1-region

In order to study the influence of altitude smearing on the determination of ionospheric parameters by incoherent scatter, we take advantage of the fact that EISCAT single pulse measurements in the F1-region have been made simultaneously with two different altitude resolutions. It is shown that the measured parameters can be very far from the real parameters, due to this altitude smearing. An attempt to deconvolve the profiles is made, which works well in the case of smooth power variations within the diffusive volume, but diverges in the case of strong structured power variations, such as those produced by energetic auroral particle precipitation into the upper atmosphere. In this last case it was, however, possible to deduce the real profile with quite good accuracy by a trial and error method. The geophysical consequences of the large discrepancy between measured and actual parameters (density and temperatures) are finally discussed.     

Small scale stratification of the mid-latitude F-region

lonograms recorded over limited frequency and height ranges have been used to reveal systematic structures on both main and range spread traces for a mid-latitude region. This fine structure has apparently not been reported previously. When disturbances are present ionogram traces are often made up of quasi-horizontal segments, suggesting that the F2-layer consists of stratified regions spaced a few kilometres apart vertically. It is proposed that if in fact stratifications are present, they may be produced by instabilities created by the presence of internal gravity waves. Interference effects on ionogram traces are also reported. These are shown to result from the presence of overlapping traces. The existence of these quasi-horizontal trace segments and interference effects is shown to contribute to the diffuseness of a range spread mid-latitude ionogram. Thus a mid-latitude range spread ionogram often appears diffuse even though the spread may consist primarily of a number of duplicate traces produced by specular reflections from a range of off-vertical angles.     

明代武昌府城江岸修筑的初步研究

在明代,由于水患频发和长江主泓变动等原因,湖广武昌府城沿江江岸屡屡崩陷,当地政府遂启动江岸修筑工程。考诸史志,明代武昌府城的江岸修筑主要约有四次,分别是正统七年(1442)、成化三年(1467)、万历十七年(1589)和万历三十四年(1606)。最终修成的江岸,自武昌府城南门望山门外(今武昌解放路南端解放桥附近)起,向西折至江边,又沿江边中经黄鹤矶向下游延伸至坛角地区(今武昌和平大道武汉工人文化宫以西),长约5公里。这条堤岸确定了武昌城沿江江岸的基线,将武昌城的城市空间扩展到江边,并延续至今。     

浙江越窑青瓷标本信息数据库管理系统的设计与实施

对文物标本进行系统分析归纳是传统工艺研究的必要途径,为实现越窑青瓷标本资料的资源共享,提高实验室工作效率,实现分析数据的科学管理,本研究开发设计了“浙江越窑青瓷标本信息数据库管理系统”.该系统基于B/S结构模式,以浙江省博物馆陶瓷标本中心的各类越窑瓷片标本来源、形态、化学成分、物理性能、显微结构、制作工艺等相关信息数据为基础,采用Wi ndows平台,以Visual Studi0 2010为开发环境,结合ASP.NET 4.0框架以及SQL Server数据库技术而构架.经过系统测试和实际运行证明,此管理系统具有良好的应用界面,交互性强,运行稳定,数据处理方便等优势,对实现古陶瓷研究信息资源共享,全面开展越窑青瓷的科学化研究提供了一个良好的数据平台.     

Transmission of large-scale TIDs in the ionospheric F2-region

Large-scale travelling ionospheric disturbances (1.s. TIDs) have been investigated in order to derive the horizontal velocity dispersion by using f₀F2 data from four ionospheric observatories in Japan. It was found that the horizontal phase trace velocity lies between 300 and 1000ms⁻¹ with periods in the range 50 to 150 min. There is evidence that the derived velocity generally increases with increase of wave period. This is consistent with the dispersion predicted by the theory of the internal gravity waves. The azimuthal angles are distributed in ±35° sectors centered around 197° (measured clockwise from north), indicating that 1.s. TIDs may be obtainable when they are excited along the auroral zone of the same sector in longitude as that of the observatories. The average propagation direction shifts by 17° from south towards west. This clockwise shift is consistent with the rotation caused by the Coriolis effect. This means that the Coriolis effect cannot be ignored for the wave propagation of 1.s. TIDs. In addition to the positive correlation between TID speed and geomagnetic activity, the direction of wave propagation is found to be correlated with polar magnetic activity. The propagation direction is mostly southward during the period of large polar magnetic disturbances, while during the period of low magnetic activity the direction scatters considerably.     

1918年在华德侨处置案引发的中外交涉

1918年北京政府和以英法为代表的协约国盟友之间,曾围绕如何处置在华德侨这个看似无关紧要的问题展开过一场外交交涉。交涉双方的行为乍看之下虽不合情理,但又是合乎逻辑的。英法等国对北京政府一再施压要求严厉处置在华德侨,与其说是为了预防敌侨捣乱,毋宁说是为了牵制北京政府;而北京政府即便是参战以后对德侨也不改宽松友善的政策,与当时中国各界对德情感氛围相匹配,其做法完全符合国际法,体现了中国近代外交理念的进步。发生在1918年的这场交涉宛如一面镜子,折射出一战期间北京政府与协约国盟友之间关系的实质。     

Midlatitude measurements of the ionospheric electric field during the ALADDIN programme

Three measurements of ionospheric electric field were made during the 24 h ALADDIN rocket programme at Wallops Island (37°50′N, 75°29′W) on June 29–30, 1974. The first of these used a double probe instrument, flown at 1500 Local Solar Time, and the second and third measurements were made by barium cloud releases at evening and morning twilight. These three electric field vectors have been compared with the predictions of a number of models of electric field due to the dynamo effects of various atmospheric tides, and also of a possible magnetospheric origin. On the assumption that the measurements were made at a location equatorward of the afternoon convergence and poleward of the morning divergence in the electric field patterns related to the Sq current cystem, Stening's model of the diurnal variation of the electric field induced by the (1, −2) tidal model at the time of the Summer solstice correctly predicts the directions of the observed electric field. Forbes and Lindzen's model, incorporating the three major propagating tidal modes as well as the evanescent (1, −2) mode, also bears an acceptable relationship to the ALADDIN electric field directions. The ALADDIN E-field magnitudes are comparable with those obtained by ground-based observations (incoherent scatter) from Millstone Hill and from Saint Santin but are about half of Stening's model values, and three times those of Forbes and Lindzen.While the Millstone Hill E-field directions are compatible with the ALADDIN observations, Saint Santin E-field directions, at the same latitude but 75° difference in longitude, are distinctly different from ALADDIN, implying that longitudinal differences are significant.     

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.     

A model of ionospheric image structure underneath a braking,cross-field plasma jet

A plasma jetting across the geomagnetic field above the ionosphere tends to brake by ohmic dissipation of Pedersen currents. The braking can affect the ionosphere underneath if the associated Pedersen drifts are intense and prolonged enough to cause cumulative image structuring. We examine such image structuring for the parameter regime of forthcoming CRRES releases, involving photo-ionization of kilograms of barium vapor moving at orbital velocity. The resultant structuring in the upper E-region offers possible diagnostic tell-tales of the braking process.     

Temporal variations of ionospheric waves in the D- and F-regions

It is shown that mesoscale ionospheric wave disturbances in the D- and F-regions regularly occur at all times of day, night and season (characteristic periods ~100, 24, 12.6 min) and are a characteristic property of dynamic processes in the ionosphere.