The coloured edge of noctilucent clouds

Noctilucent clouds sometimes show a clearly defined upper edge, caused by the edge of solar illuminance under twilight conditions (the shadow of the Earth). Usually the clouds at this edge share the bluish white colour of the clouds lower down, but on occasion a deep red colour can be seen. It is shown here that the cause is simply optical absorption in the Earth's atmosphere, particularly as modified through absorption by atmospheric ozone in the (visual) Chappuis bands.     

The atmospheric electrode effect over snow

The atmospheric electrode effect is treated both in the turbulent and non-turbulent cases. For the non-turbulent case it is shown by geometrical considerations that field-free regions near the ground act as an effective ion supply reducing the electrode effect, except in winter when the snow forms a smooth ground. The equations with turbulence are linearized and solved analytically assuming that the charged aerosol remains uniformly distributed owing to its long time of recovery from turbulent fluctuations. Data from continuous measurement of the difference of positive and negative conductivity, which is proportional to the space charge density, show good agreement with theory in both cases, provided that the air is stable near the ground when the positive conductivity is less than about 6 fS m⁻¹ during fair weather.     

The potential gradient sunrise effect in atmospheric electricity

Experimental results are produced which show that the early part of the sunrise effect is apparently not related to variations in the temperature or humidity of the lower atmosphere. An electrode effect space charge layer tends to obscure rather than enhance the effect. The expected seasonal variation in the sunrise effect was not found. Two possible explanations of this are suggested.     

The transformation of the Irish border

This article introduces a special issue dealing with partition and the reconfiguration of the Irish border. Notwithstanding southern nationalist refusal to accept the partition of Ireland in 1921, the border gradually consolidated its position. The article describes the transformation in relations across the Irish border which first found a place on the political agenda in the early 1970s, but which was given full institutional expression only following the Good Friday agreement of 1998. This new configuration has two aspects, which seem at first sight to be in conflict with each other: it marks a new, unreserved acceptance of the legitimacy of the border by Irish nationalists (though moderated by British agreement to end partition if the two parts of Ireland so wish), and it is characterised by a significant growth in public sector bodies which span the border.     

The desert,the border,and the city: Staging a spectacle on the Chile-Peru border

The 1970s saw Chile and Peru, both headed by military dictators, come to the brink of war. In order to avoid such a war, the Chilean military in the far north engaged in techniques of ‘spectacle’ for two reasons: firstly, to convince citizens on both sides of the border that Chile had a strong military and would succeed in the event of a war with Peru, and secondly, to create the impression of ‘fraternity’ with Peru. To perform these spectacles, the Chilean military employed the geography of northern Chile in three spaces: the desert, the border, and the city. These spaces became stages where acts of military deception could be implemented with the Chileans using fake tanks, military ceremonies, and bogus parades to appear militarily strong. This extends current scholarship by arguing that multiple environments can be harnessed for their specific geographical qualities in order to stage a unified geopolitical spectacle. Previous geographical scholarship has focused on individual environments as military spaces and scholarship on spectacle has treated environments as a backdrop and not a central part of how the spectacle is enacted. Here I show that it was the precise natures of the border, the desert, and the city that were exploited for a multi-scaled, heterogeneous, and fractured form of spectacle. Through the orchestrated control of these three spaces that define the border region, a clear narrative of military strength matched with a desire for peaceful co-operation with Peru was created.     

Measurements of noctilucent cloud heights: a bench mark for changes in the mesosphere

Recent studies of noctilucent clouds indicate a secular increase in their frequency of occurrence which may be associated with changes either in the water vapour concentration or in the mean temperature of the mesopause. Noctilucent clouds are expected to be seen very close to the level where the relative humidity is 100% and changes in temperature of the mesosphere or in its water vapour content might be expected to alter the height at which the clouds occur. Comparison of our height measurements with those obtained over the past 100 yr shows that the suggested changes since 1885 in temperature (a decrease of approximately 7°C) and water vapour mixing ratio (an increase of approximately 1.7 ppmv) have not been sufficient to affect the height of the clouds by an observable amount. Future height measurements of noctilucent clouds may provide a practical indicator of changes taking place in the mesosphere which could be associated with global-scale alterations of the lower atmosphere.     

The influence of ionization and recombination processes on the dynamics of ionospheric plasma clouds

The dynamics of a one-dimensional ionospheric irregularity interacting with the magnetosphere is studied by numerical simulation. The polarization electric field produced by charge separation within the irregularity propagates along magnetic field lines with the Alfvén velocity V_A and drives polarizational and field-aligned currents in the magnetosphere. Their values and localization are controlled by motion and deformation of the irregularity resulting from its electrostatic coupling to the background ionosphere. The pattern of the field-aligned currents varies with time and depends primarily on gradients of the polarization electric field. The latter is controlled by the ambient electric field, diffusion, recombination process, intensity of the initial perturbation, etc. Feedback effect of the magnetospheric conductance on the development of the irregularity is examined.     

论清末的省界观念

清末的省界观念,学界对其在多个领域中的普遍存在缺乏清晰的认识和更进一步的探究.其实,到了清末,以地缘情结为基础的省界观念无论是在地方政权体系、私营经济领域当中,还是在留学生特别是留日学生群体、资产阶级革命派当中,都广泛地存在着,并产生着极其恶劣的影响.直到21世纪的今天,省界观念依然如幽灵一般无处不在,因此,涤荡省界意识,有着重要的现实意义和价值.     

Foil chaff clouds as a tool for in-situ measurements of atmospheric motions in the middle atmosphere: their flight behaviour and implications for radar tracking

The aerodynamic behaviour of foil chaff (rectangular plates) used for in-situ measurements of atmospheric motions in the middle atmosphere (up to 100 km altitude) can be described by Stokes' Law in which the corrections are applied to the coefficient of viscosity. The results obtained with this approximation are in good agreement with observations and allow us to explain in detail certain peculiarities occasionally seen in the tracking of chaff clouds by radar.     

Ionospheric trends in mid-latitudes as a possible indicator of the atmospheric greenhouse effect

Using long-term ionosonde measurements in mid-latitudes (Juliusruh: 54.6°N, 13.4°E; 1957–1990), the first experimental hints of a decrease of the peak height of the ionospheric F2-layer were found. In contrast to that the long-term variations of the peak electron densities in the F2-layer, as well as the E-layer, are small. These results qualitatively agree with the predictions of Rishbeth [(1990) Planet. Space Sci.38, 945] who expected a lowering of the E- and F2-layer caused by a global cooling of the strato, meso- and thermosphere due to the increasing greenhouse effect.     

Unwanted sea migrants across the EU border: The Canary Islands

In the early 2000s, the Canary Islands emerged as the main gateway for unwanted sea migrants from Senegal into Spain. In this paper, I draw from a year of multi-sited ethnographic work to discuss the relationship between state actions to secure the border against these migrants, on the one hand; and smugglers and migrants' efforts to subvert those actions, on the other. My argument is that the relationship between the two is mutually constitutive: anti-immigration policy is a reaction to the actions of unwanted migrants, and unwanted migrants adapt to state efforts to seal the border against unwanted migration by finding and exploiting spaces of opportunity in the border. In the context of sea migration from Senegal to the Canary Islands, 2005 marks a major shift in this relationship. That year the European Union adopted a new framework for migration control (the Global Approach to Migration and Mobility), Frontex became operational, and Spain and Senegal deepened their cooperation to stop unwanted Europe-bound sea migration. This forced unwanted migrants to find creative ways to enter EU territory. I argue that combining the institutional and migrant perspectives allows us to explore the decentering of the state in the contemporary anti-immigration border regime, the emerging spatialities of the contemporary border, and understand the migrant's journey. This perspective also illuminates the messiness, violence, and multiplicity of interests involved in the bordering of Europe.     

论清代长城边口贸易的时代特征

Comparison study on the border trading between the Ming and the Qing dynasties shows that during the Qing Dynasty, the Great Wall become an important means for the government to rule other nations like Mongolian; the border trading markets in the Qing were more than that in the Ming, and the folk trading along the Great Wall played an important role; the management about the border trading by the Qing government was embodied in the control of the structure and scale of border trading market and the mutual trading; the trading premise, the market nature, the market value for existence, and the market function of the border trading in the Qing were different from that of the Ming Dynasty. Translated by Chen Cheng from Qingshi Yanjiu 清史研究 (Studies in Qing History), 2007, (3): 73–86     

The cross-border reterritorialization concept revisited: the territorialist approach applied to the case of Cerdanya on the French-Spanish border

The aim of this paper is to bring new elements into the theoretical discussion so as to better understand the realities of borderlands. Our goal involves projecting a new conceptualization of the cross-border territory and cross-border reterritorialization by refining the analytical framework envisioned by the current literature on border studies. More specifically, we apply the so-called ‘territorialist approach’, an innovative and culturally oriented approach for territorial studies that is rooted in the Italian geographical school. Cross-border territories are conceived as complex territorial units, whereby geographical, socioeconomic and cultural patterns are affected and thus altered by the fixation of international boundaries and territorialization. Nevertheless, the persistence of local cross-border networks, both formal and informal, contributes to the maintenance of a shared local milieu. The European integration processes, especially in view of the European Territorial Cooperation programmes, represent an important framework for supporting local cross-border cooperation and boosting new territorial strategies for borderlands. From this perspective, we hypothesize that new cycles of local cross-border reterritorialization can be observed along the EU borderlands by creating new forms of cross-border territorial capital. The case study of Cerdanya (French-Spanish border) illustrates the application of the theoretical framework by analysing the enduring experiences of cross-border cooperation.     

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.     

The wall and the wash: Security,infrastructure and rescue on the US‐Mexico border

Based on ethnographic research with firefighters trained as EMTs (emergency medical technicians) or paramedics in northern Sonora and southern Arizona, this article takes the vantage point of emergency responders on both sides of the US‐Mexico border to trace the harmful effects of the security assemblage on those who inhabit and trespass this militarized landscape. Interested in the materiality of security – how its discursive and affective qualities are anchored in urban and desert terrain by means of infrastructure and technology – this article focuses on two such ‘anchors’, the wall and the wash, in order to address the legal and ethical issues that result from the deployment of tactical infrastructure on the border.     

The effects of neutral winds on the propagation of medium-scale atmospheric gravity waves at mid-latitudes

The influence of neutral winds on the propagation of medium-scale atmospheric gravity waves at mid-latitudes is investigated. A 3-dimensional neutral wind model is developed and used together with an atmospheric model in a gravity-wave ray-tracing analysis. It is demonstrated that the thermospheric wind can act as a filter for waves travelling at unfavorable angles to the mean flow, via the mechanisms of reflection and critical coupling. This wind filtering action rotates clockwise diurnally through 360° in the northern hemisphere. Observational evidence is presented which supports these predictions. Extensive modelling indicates that (a) faster and longer period waves are least affected by the neutral winds and (b) fixed-height (e.g. HF Doppler) observations of medium scale gravity waves is only likely to be possible for waves generated locally (within 500–1000 km). Waves generated at greater distances are probably dissipated before reaching the observation region.