Longitudinal difference in the Sq profiles in the South American region

The average daily variation profiles of the H component at Huancayo on the west coast and Eusébio, Fortaleza, on the east coast in the dip equator region and La Quiaca near the west coast and Vassouras near the east coast in the southern low latitude region of the South American continent indicate that the profiles are broader for the east coast. Thus, distortions in the overhead current systems while passing from one coast to the other are indicated.     

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.     

Structure in the seasonal variations of Es at southern latitudes

The diurnal variations of the seasonal characteristics of sporadic-E occurrence have been studied by analyzing a large data set of ionosonde parameters for two southern hemisphere stations. The seasonal patterns are found to display anomalous short-term variations apparently not associated with solar control or the effects of dynamic meteorology.     

The effect of the electric field and neutral winds on E-region ion densities and conductivities at low latitudes

A model to calculate electron densities and electrical conductivities in the ionospheric E-region at low latitudes has been developed. Calculations have been performed under photochemical equilibrium and including plasma transport due to the electric field and neutral winds. Results have been compared with observations at Arecibo (18.15°N, 66.20°W), Thumba (8°32′N, 76°51′E) and SHAR (14.0°N, 80.0° E). Good agreement is obtained for Arecibo. For Thumba and SHAR agreement is satisfactory for altitudes above 110 km. Below 100 km, model predictions are too low in comparison with the observed data. The effect of plasma transport on electron densities and Hall and Pedersen conductivities is investigated in detail. A combination of neutral winds and a downward (or westward) electric field can compress the plasma into a thin layer. An upward electric field along with the neutral winds gives rise to a broad, multilayered profile. The ratio of height-integrated Hall to Pedersen conductivities changes from 1.2 to 2 in some cases.     

Concentrations of H2O and NO in the mesosphere and the lower thermosphere at high latitudes

Water vapour and nitric oxide concentrations in the mesosphere and lower thermosphere were derived from infrared emission and positive ion composition measurements above northern Europe during the Energy Budget Campaign 1980. The experiments were performed at different levels of geomagnetic disturbance. Both water vapour and nitric oxide are highly variable. Water vapour mixing ratios between 0.2 ppm and 10 ppm were observed. The nitric oxide peak densities varied by more than a factor of ten. Maximum values of 2 × 10⁹cm⁻³ were obtained.     

新南方起源时期美国南方城市的发展和城市生活的变迁

新南方起源时期南方城市有显著发展,数量明显增加并初步完成城市功能的转换和城市设施的更新,为以后新南方综合性大都市的出现打下基础。但与同时期的北方城市相比,南方城市规模小,对农作物,工业原料和铁路的依赖严重,乡土气息浓厚。城市社会形态特征表现为种族隔离加剧,城市成为种族冲突的温床,一个自主自立的黑人社区形成;新老城市社会氛围差异大,老城市的相对静态与新兴城市的动态形成鲜明对照,南方社会重心不仅从农村移到城市,而且从老城市移到新兴城市。新兴城市逐渐成为南方城市发展的亮点和方向。     

The characteristics of VHF echoes from the summer mesopause region at mid-latitudes

Radar observations have been carried out at Aberystwyth (52.4°N, 4.1°W) during the period May–August 1990 to search for echoes analogous to the Polar Mesosphere Summer Echoes commonly observed at high latitudes. Signal strength measurements in the vertical and at 12° from the vertical are used to examine the aspect sensitivity of echoes, and Doppler measurements at 6° from the vertical and in the vertical to estimate wind velocities. The observations show the presence of two types of moderately strong echoes from heights above 80 km. On most days a spectrally broad echo is observed with characteristics consistent with isotropic turbulence scatter. On certain days between mid-June and mid-July, stronger spectrally narrow echoes are observed with characteristics similar to Polar Mesosphere Summer Echoes.     

Modelling studies of the conjugate-hemisphere differences in ionospheric ionization at equatorial anomaly latitudes

The relative importance of the equatorial plasma fountain (caused by vertical E x B drift at the equator) and neutral winds in leading to the ionospheric variations at equatorial-anomaly latitudes, with particular emphasis on conjugate-hemisphere differences, is investigated using a plasmasphere model. Values of ionospherec electron content (IEC) and peak electron density (Nmax) computed at conjugate points in the magnetic latitude range 10–30° at longitude 158°W reproduce the observed seasonal, solar activity, and latitudinal variations of IEC and Nmax, including the conjugate-hemisphere differences. The model results show that the plasma fountain, in the absence of neutral winds, produces almost identical effects at conjugate points in all seasons; neutral winds cause conjugate-hemisphere differences by modulating the fountain and moving the ionospheres at the conjugate hemispheres to different altitudes.At equinox., the neutral winds, mainly the zonal wind, modulate the fountain to supply more ionization to the northern hemisphere during evening and night-time hours and, at the same time, cause smaller chemical loss in the southern hemisphere by raising the ionosphere. The gain of ionization through the reduction in chemical loss is greater than that supplied by the fountain and causes stronger premidnight enhancements. in IEC and Nmax (with delayed peaks) in the southern hemisphere at all latitudes (10–30°). The same mechanism, but with the hemispheres of more flux and less chemical loss interchanged, causes stronger daytime IEC in the northern hemisphere at all latitudes. At solstice, the neutral winds, mainly the meridional wind, modulate the fountain differently at different altitudes and latitudes with a general interhemispheric flow from the summer to the winter hemisphere at altitudes above the F-region peaks. The interhemispheric flow causes stronger premidnight enhancements in IEC and Nmax and stronger daytime Nmax in the winter hemisphere, especially at latitudes equatorward of the anomaly crest. The altitude and latitude distributions of the daytime plasma flows combined with the longer daytime period can cause stronger daytime IEC in the summer hemisphere at all latitudes.     

内战以后美国南部的“农业阶梯”问题

农业阶梯理论以土地所有权的有无和程度为衡量标准 ,意在揭示人们从租佃农向自耕农的奋斗历程。本文在考察了内战以后美国南部种植园地区租佃农经济地位的变动状况之后得出结论 :南部不但不存在“农业阶梯” ,反而存在一种“反阶梯”趋势 ,这种趋势根源于南部自身的社会经济 ,而其根本推动力是大西洋经济圈资本主义经济的发展。     

试探美国南部奴隶制种植园的形成

美国南部的奴隶制种植园形成于殖民地时期。种植园最初在北美大陆出现之际,主要是指在开拓的一块土地上相对集中地生产市场所需要的大宗商品作物,它并没有特定的劳动制度。黑人奴隶制的劳动制度是在以后的发展中逐渐形成的历史特征。在以弗吉尼亚和马里兰为中心的上南部和以南卡罗来纳为代表的下南部,奴隶制种植园经历了不同的形成道路。上南部的烟草种植园在北美奴隶制种植园的形成和发展过程中占据主导地位。奴隶制种植园对美国南部近代社会经济和历史发展产生了巨大而深远的影响。     

Ion composition changes during F-region density depletions in the presence of electric fields at auroral latitudes

F-region density depletions in the afternoon/evening sector of the auroral zone are studied with the EISCAT UHF radar. Four case studies are presented, in which data from three experiment modes are used. In each case the density depletion can be identified with the main ionospheric trough. For the two cases occurring in sunlit conditions the electron densities recovered significantly after the trough minimum. Tristatic ion velocity measurements show the development of poleward electric fields of typically 50–100 m Vm⁻¹, which maximize exactly in the trough minimum. A special analysis technique for incoherent scatter measurements is introduced, based on the ion energy equation. By assuming that the ion temperature should obey this equation it is possible to fix this parameter in a second analysis and to allow the ion composition to be a free parameter. The results from two experiments with accurate velocity measurements indicate that the proportion of O⁺ near the F-region peak decreased from 100% in the undisturbed ionosphere to only 10% and 30%, respectively, in the density minimum of the trough. The loss of O⁺ is explained by the temperature dependence of recombination with nitrogen molecules. Temperatures derived from radar measurements are very sensitive to the assumed ion composition. For the above case of 10% O⁺ the deduced electron temperature in the trough was transformed from a local minimum of < 2000 K to a local maximum of 4000 K.     

Propagation characteristics of night-time whistlers in the region of equatorial anomaly

In this paper results of simultaneous multi-station observations of night-time whistlers obtained at very low latitudes for the last three years are presented. The propagation mechanism of these whistlers is also discussed. Some records can be shown to have the characteristics of ducted propagation by calculating the dispersion of the whistlers along a ducted path and by noticing the feature of strong intensity, as well as the existence of three-hop echoes. Whistlers in some other records, however, can be shown to be propagating along a non-ducted path by numerical ray-tracing, in which a non-dipole field (IGRF) is used and a negative horizontal gradient of ionization in the equatorial ionosphere is taken into account. The agreement of the results of calculation with observed facts seems to confirm the existence of a definite whistler path at very low latitudes. Finally, based on analysis of typical events, the effects of magnetic storms on the parameters of low latitude whistlers due to variations in the equatorial ionosphere are also discussed.     

Observation of low energy particle precipitation at low altitude in the equatorial zone

Precipitation of protons (~ 1 MeV) in the equatorial zone was investigated by the Phoenix-1 experiment on board the S81-1 mission from May–November, 1982. The protons show a precipitation peak along the line of minimum magnetic field strength with a full width at half maximum (FWHM) of 13°. The index of equatorial pitch angle distribution is q ~ 19. The peak proton flux shows a fifth-power altitude dependence, and the proton flux shows approximately a factor of 3 times increase in 1982 compared to that in 1969 due, possibly, to the stronger (~ 1.2 times) solar maximum conditions of 10.7cm radiation in 1982.     

The Politics of Policy Circulation: Unpacking the Relationship Between South African and South American Cities in the Adoption of Bus Rapid Transit

This paper utilizes the introduction of bus rapid transit (BRT) in South Africa to unravel the role of South–South connections in local policymaking. While the South African systems are unmistakably modeled after Bogotá's Transmilenio, whose accomplishments have been touted as the low‐cost, high‐quality transport solution, the process through which other Southern cities influenced the circulation of BRT remains underexplored. In so doing, this paper asks how and why certain cities are brought into conversation with one another and what happens as a result? This analysis suggests that policy circulation is never a rational survey of best practices but a political process through which policymakers select their sites of learning in accordance with wider aspirations, ideologies and positioning. Illustrating the way in which policymakers deploy different meanings of the global South and their position within this construct to justify local policy decisions adds a critical dimension to understandings of policy mobilities.     

Practising Development at Home: Race,Gender, and the “Development” of the American South

Drawing on a range of works that extend from gendered historical analyses of colonialism to critical histories of development, and based on archival research in Alabama, Arkansas, and Mississippi, I argue in this paper that what we now call international development—a form of hegemony different from but related to colonialism—needs to be understood not only as a geopolitical tool of the Cold War, but also as a technique of governance that took shape within the realm of the domestic and through a racialized gaze. I do so by tracing some of the key elements of the US international development practices in the postwar era to a different time and place: the American South, a region considered “undeveloped” in the first decades of the twentieth century, and the agricultural extension practices that targeted the rural farm home and farm women, particularly African‐American women.