The nocturnal intermediate layer over South Georgia

Detailed analyses of ionograms from South Georgia (54°S, 37°W; L = 1.9) show that a nocturnal intermediate layer is frequently seen between the E- and F-regions in the height range 130–180 km. The occurrence of the intermediate layer is almost totally restricted to the winter months and between the local hours of 1930 and 2300. The intermediate layer event is characterized by a prior downward movement of the F-layer, followed by the formation of the intermediate layer and its subsequent drift downwards to about 140 km. Initially, the layer is thick (~ 10–20 km), but gradually thins as it evolves. The occurrence of the intermediate layer appears to be independent of the level of magnetic activity. Observations of intermediate layers from other localities, which are briefly reviewed, are compared with those made at South Georgia. Some similarities and differences are identified.Mechanisms which account for the formation of the intermediate layer at South Georgia are considered, It is shown that the main features of the diurnal and seasonal variations of occurrence can be adequately explained by the theory of convergence of ionization driven by the solar semi-diurnal tidal winds. Some limitations of this theory are discussed, as it cannot account for all the features seen at this southern midlatitude observatory.     

Interaction of solar wind with the magnetopause-boundary layer and generation of magnetic impulse events

The transport of mass, momentum, energy and waves from the solar wind to the Earth's magnetosphere takes place in the magnetopause-boundary layer region. Various plasma processes that may occur in this region have been proposed and studied. In this paper, we present a brief review of the plasma processes in the dayside magnetopause-boundary layer. These processes include

• 1.(1) flux transfer events at the dayside magnetopause,
• 2.(2) formation of plasma vortices in the low-latitude boundary layer by the Kelvin-Helmholtz instability and coupling to the polar ionosphere,
• 3.(3) the response of the magnetopause to the solar wind dynamic pressure pulses and
• 4.(4) the impulsive penetration of solar wind plasma filaments through the dayside magnetopause into the magnetospheric boundary layer. Through the coupling of the magnetopause-boundary layer to the polar ionosphere, those above processes may lead to occurrence of magnetic impulse events observed in the high-latitude stations.

     

The influence of ionospheric absorption on mid-latitude whistler mode signal occurrence from VLF transmitters

Whistler mode signals from VLF transmitters received at Faraday, Antarctica (65° S, 64° W) during 1986–1991 show an annual variation in the number of hours over which signals are observed, with a maximum in June and a minimum in December. The variation was larger at solar minimum than at maximum and can be understood in terms of changes in absorption of VLF signals in the D-region, where the high geographic latitude of Faraday plays an important role in producing low attenuation levels during the austral winter. In contrast, very little such variation was observed at Dunedin, New Zealand (46° S, 171° E) in 1991. Nighttime whistler mode signals have start and end time trends that are consistent with the influence of F-region absorption. Increases in whistler mode occurrence appear to be associated with periods of high geomagnetic activity at solar maximum but not during solar minimum. A possible mechanism involving decreased F-region absorption is discussed.     

挺进皖南:1949年干部南下与政权接管

1949年干部南下是中共中央为了接管和巩固长江以南新解放区政权而作出的一项重大战略决策。其中,挺进皖南是干部南下的重要目标之一。但是,相对于沪宁杭而言,学界对干部挺进皖南的研究几近空白。本文通过查阅、梳理相关档案材料,初步考察了挺进皖南的干部来源、规模、分配任用等情况,揭示了他们在解放初期皖南政权接管中的重要作用。     

The influence of sunspot number and magnetic activity on the diurnal variation of the geomagnetic field at mid to high latitudes

The variations of the diurnal range of the geomagnetic field with sunspot number and with magnetic activity was studied at mid and high latitude stations in the northern hemisphere at different seasons. The effect of increasing sunspot number is small at lower latitudes and increases with geomagnetic latitude, while the effect of increasing magnetic activity is to increase the range at all latitudes, very greatly at the higher geomagnetic latitudes.     

中日对抗与公共卫生事业领导权的较量——对"南满洲"铁路、港口中心城市的观察(1901-1911)

1905年日俄战争之后,日本在南满控制区域内的铁路、港口中心城市大力推进公共卫生事业,与此同时,中国官府也积极创办当地公共卫生事业,双方就公共卫生事业领导权展开激烈的竞争和较量,并在一定程度上改善了某些特定区域的卫生环境。然而,由于这是一种扩张/反抗的展开模式,在疾病治疗和预防疾病之外被赋予了更多的政治考量,致使城市贫民区与乡村的医疗卫生条件并未得到重点关注和大量投入,很长一段时间内该地区仍然疾病丛生,恶性传染病蔓延。在这个意义上,日本推进的公共卫生事务自然有其殖民主义扩张、帝国主义统治处心积虑、老谋深算的一面,中国官府和社会的自强卫生、救国医学则或可被视为一种不得已的推进方式。     

The new South Africa's foreign policy: principles and practice

This article outlines principles which, shortly before taking office in 1994, the ANC said would be the foundation for its future foreign policy. The ANC stated that their core concern was the pursuit of 'human rights', which were directly related to the promotion of democracy. Other principles included respect for international law, support for peace and disarmament, and universality. These were to be pursued in four settings. First, the global division between the First and Third Worlds as the government was concerned about economic inequality and unjust global trading systems. Second, international organizations as these were seen as central to the search for human rights, peace and equality. Third, demilitarization resulting in South Africa's forces being used for self-defence and peacemaking and keeping only. The government believed that this would produce savings which could be redirected into social development. Finally, supporting the rest of Africa as the ANC believed South Africa could not flourish if surrounded by poverty. The article examines how far the ANC governments of Presidents Mandela and Mbeki have succeeded in implementing the principles, and how far they have fallen short. The article also includes a discussion of Mbeki's policy towards Robert Mugabe of Zimbabwe.     

The Commonwealth and South Africa: From Smuts to Mandela

The creation of modern South Africa as an independent unitary state within the British Empire (c. 1910) gave birth to the Commonwealth idea. Jan Smuts’s views on Commonwealth were formative and they continued to inform the evolution of the organisation until the end of the Second World War. Also significant was the role played by Afrikaner nationalist leader J. B. M. Hertzog, who exerted a critical influence on the 1926 Balfour Declaration and Statute of Westminster. At the point of South Africa’s departure from the Commonwealth in 1961, the Commonwealth divided between new entrants, who cast South Africa as a pariah, and older member states who lamented the exit of a troubled family member. Even after South Africa’s departure from the Commonwealth in 1961, apartheid’s significance as the global exemplar of institutionalised racism and colonial rule helped to bind the Commonwealth as a multi-racial organisation with strongly defined ethical values. South Africa’s reintegration in 1994, with Nelson Mandela to the fore, was welcomed as a triumph for the Commonwealth. Paradoxically, however, this proved a pyrrhic victory and may actually have contributed to the Commonwealth’s state of indirection.