VHF transequatorial propagation via three dimensional waveguides

The three dimensional model of VHF propagation along ionospheric waveguides or ducts developed by Platt I. G. and Dyson P. L., 1989 [J. atmos. terr. Phys. 51, 897–910] has been used to study transequatorial propagation (TEP) along equatorial bubble irregularities aligned along the earth's magnetic field. Bubbles with circular and elliptical cross-sections and different apex heights have been used to determine the region illuminated in the conjugate hemisphere by TEP and the power of the signals. The results show that the three dimensional waveguide model can explain many features of TEP, including those not well explained by the simpler waveguide models used previously. The calculations therefore confirm that TEP can be caused by guided propagation along equatorial bubble irregularities aligned along the magnetic field. The results show that a bubble located on the transmitter's longitude can illuminate a wide area of the conjugate hemisphere. A well defined maximum central power region occurs which in most cases is centred at a latitude slightly lower than the conjugate of the transmitter. Bubbles with circular cross-section can illuminate a region more than ten degrees in latitudinal extent and five degrees in longitude. Bubbles which are vertically elongated at their apex illuminate a much narrower region in longitude. TEP between points with relatively large separation in longitude can result from either leaky rays or ducts tilted out of the magnetic meridian plane. This explains some observations of TEP previously thought to be inconsistent with waveguide propagation. The variation of power loss with frequency depends on a number of factors such as bubble shape and height. Co-ordinated experiments involving a transmitter and several receivers in the conjugate hemisphere should enable properties of bubbles to be determined.     

Modelling of transequatorial propagation of HF radio waves

In the geometrical optics approximation, a synthesis oblique ionogram of ionospheric and magnetospheric HF radio wave signals propagating between magnetic conjugate points has been carried out. The magnetospheric HF propagation is considered for a model of the waveguide formed by field-aligned irregularities with depleted electron density. The characteristic peculiarities of the magnetospheric mode have been determined: (i) strong disperion of the group delay with a frequency at 14–18 MHz, from − 1.4 to 0.6 ms/MHz for magnetically conjugate points at geomagnetic latitudes φ = 30°, 40° and 50°, respectively, (ii) spreading ∼ 1–2 ms, and (iii) a possibility of propagation between magnetic conjugates points at moderately low geomagnetic latitudes φ₀ ∼ 30–40° at frequencies exceeding 1.5 times the maximum usable frequency (MUF) of multi-hop ionospheric propagation.     

Application of a scattering theory of VHF transequatorial propagation

Numerical application is made of the theory of scattering by long, curved, field-aligned irregularities of ionization density in the F-region developed by Ferguson and Booker. Using an intermediate-scale regime of irregularities with an outer scale equal to the scale height of the F-region and an inner scale equal to the ion gyroradius, combined with a small-scale regime with an outer scale equal to the ionic gyroradius and an inner scale equal to the electron gyroradius, calculations are made corresponding to (i) equatorial spread-F in the VHF and UHF bands, (ii) long-range transequatorial propagation of the type observed by Nielson and (iii) short-range transequatorial propagation of the type observed by Cohen and Bowles. The same ionospheric model yields field-strengths of the right order of magnitude in all three cases. The theory also predicts a focusing phenomenon that should be looked for experimentally.     

Anomalous interference in Omega VLF wave propagation on east-to-west equatorial paths

The phase of Omega Haiku (Hawaii U.S.A.) signals has been measured at 13.6 and 10.2 kHz on-board ship from Tokyo to Fremantle, Australia, during the early parts of the winters of 1979 and 1980. Short-term (∼- 1 h) fluctuations are observed on the phase of the Haiku signals as received around the geomagnetic equator at a distance of 8000 km west of the transmitter. Phase cycle slippings take place frequently in association with the phase fluctuations, the occurrence frequency of which is a maximum at 6 S geomagnetic latitude. These propagation anomalies are a consequence of the passage of the ship through an interference pattern the spacing distance of which is about 11 km at 13.6 kHz —one-half of the wave-length of the transmitted wave. It is concluded that the interference is caused by the signal propagated directly from the transmitter and the long-path signal propagating a distance of 32.000 km in the west-to-east direction. This result implies that the attenruation of the east-to-west propagating Omega wave is anomalously great at the equator, in pood agreement with calculated values based on the Galejs' anisotropic waveguide model.     

Field aligned airglow observations of transequatorial bubbles in the tropical F-region

It is possible to form images of the tropical F-region ionization structures, variously labelled as ‘bubbles’, ‘plumes’, or ‘depletions’, in a plane perpendicular to the magnetic field by observing the airglow emissions associated with them in a field aligned direction. Structures which are present at altitudes from 250 km to more than 700 km above the dip equator map down to the 250–350 km region, where recombination and associated airglow emissions occur, ranging from the equator to dip latitudes of 15° or more. The structures can be viewed in a field aligned direction from sites in the range 17°–23° dip latitude. Measurements with high angular resolution (as small as 0.1° in the meridian) could show structures as small as 2 km. It is possible to make simultaneous measurements in both 6300 and 7774 Å recombination emissions, from which the height h_max of the peak plasma concentration n(e)_max on the field line can be estimated from a ratio of the emission rates. It is possible to make maps of n(e)_max and h_max either by raster scanning the sky in the two emissions or by imaging them onto an imaging detector. Useful data can be obtained from one site over a range of 20° in dip latitude and 10° in dip longitude. Observations in the same magnetic meridian as a backscatter radar system are desirable, as also are observations from near magnetic conjugate points. Imaging characteristics for the observation sites in the range of dip latitude 17°–23° have been calculated.     

On the phase changes between oscillations in the group and phase paths due to TIDs

The changes in phase path. ΔP, and group path, ΔP′, of a fixed frequency CW transmission were obtained over a ground range of ≈ 120 km. During the passage of TIDs through the ray path, changes in phase of 180° between ΔP and ΔP′ were found to occur over several cycles. A simple model incorporating moving triangular irregularities superimposed on a linear background electron density profile was used to calculate ΔP and ΔP′, and using this model, phase shifts between ΔP and ΔP′ were found which were similar to those encountered experimentally.     

Design paths of federal intergovernmental cooperation

Actors rarely approach institutional design choices with a blank slate but are influenced by design choices made at earlier stages. How does institutional design evolve over time and are there specific paths to deepening cooperation? We investigate the institutional design paths of subnational cooperation that are chosen to address increasingly complex and interconnected policy problems. We theorize that besides the substantive problem, earlier choices matter to explain what institutional design mechanism is chosen; that is, the design of existing institutions between two subnational governance units, called substates, influences the design of subsequent institutions. Using a semi-parametric Cox proportional hazards model, we show that the design paths of subnational cooperation in the Swiss water governance sector correlate with earlier design choices. Our results indicate that not all cooperation is self-reinforcing and path-dependent, but they show which specific design choices are more likely to follow each other in repeated formal federal intergovernmental cooperation.     

On the influence of a plasma hot component on whistler propagation beyond the plasmapause

Theoretical spectrograms are computed for whistlers propagating beyond the plasmapause. The electron distribution function was modelled as consisting of a hot plus a cold component and an appropriate dispersion equation is used. A collisionless (CL) model is used for the cold electron concentration and for the hot electron component the derived model assumes a bi-maxwellian distribution function with a loss cone at the equator. The results indicate limits on the use of the cold plasma approximation (c.p.a.) in the study of magnetospheric whistler propagation beyond the plasmapause and show that whistler analysis with the c.p.a. may under or overestimate the L value of the path deduced from ground spectrograms, depending on the anisotropy of the hot component.     

Ionospheric whistler propagation

In a previous paper (Thomson Dowden 1977) it was found that down-going whistlers exit from ducts a few hundred km above the ISIS II altitude of 1400 km, a result confirmed here. Using a set of models chosen to fit the full range of variability of density versus latitude profiles measured at ISIS II altitude we now show by ray-tracing that transmission from duct to ground and from ground to duct is most likely for duct entry/exit in the altitude range 1200–1500 km. Thus as far as whistler trapping is concerned, ducts terminate at altitudes well above 1000 km, considerably higher than has been generally thought.Several consequences of this are discussed. Direction finding measurements on the ground will underestimate the L-value of ducts by 0.2 to 0.3. Of the whistler energy exiting from a given duct and reflected from the base of the ionosphere, only a small fraction will re-enter that duct, implying that 10–20 dB of magnetosphere amplification per hop is needed to sustain multi-hop whistlers and mid-latitude hiss. On the other hand some of the reflected energy may enter adjacent ducts, thus supplying a ready explanation for mixed-path whistlers.     

Ionospheric propagation of ULF-waves

Features of mid-latitude ionospheric propagation of geomagnetic pulsations are studied. It is shown that the orientation of the horizontal component of the incident wave vector with reference to the geomagnetic meridian has a strong influence on the amplitude transformation and on the angle of rotation of the polarization plane. The effect of different conductivities of the Earth's crust and the contribution of Hall currents to the total pulsation field in the case of an inclined geomagnetic field are also considered.     

Ray-tracing the paths of very low latitude whistler-mode signals

VLF whistler-mode signals with very low group delays (75–160 ms) received at night in Dunedin, N.Z., from the 23.4 kHz MSK transmissions of NPM, Hawaii (21.5°N, 158°W), are explained by ray-tracing along unducted paths. The typical vertical and horizontal electron density gradients of the night equatorial ionosphere are found to be sufficient to explain not only the typical group delays but also their decrease during the night and the typical frequency shifts observed on these signals. An important feature appears to be the decreasing starting and finishing latitudes (and the decreasing maximum height of the path) during the course of the night. The amplitude of the signals in relation to the expected collisional absorption in the ionosphere is discussed. A simple but quite accurate analytical expression suitable for ray-tracing is derived for the night electron density in the height range 170–1400 km, based on non-isothermal diffusive equilibrium and O⁺/O friction.     

Cultural policies for sustainable development: four strategic paths

Abstract

In the Sustainable Development Goals adopted by the United Nations in 2015, the role of culture is limited. We argue that culture’s absence is rooted in the longue durée of interplay among theoretical and policy debates on culture in sustainable development and on cultural policy since the mid-twentieth century. In response to variations in concepts and frameworks used in advocacy, policy, and academia, we propose four roles cultural policy can play towards sustainable development: first, to safeguard and sustain cultural practices and rights; second, to ‘green’ the operations and impacts of cultural organizations and industries; third, to raise awareness and catalyse actions about sustainability and climate change; and fourth, to foster ‘ecological citizenship’. The challenge for cultural policy is to help forge and guide actions along these co-existing and overlapping strategic paths towards sustainable development.     

Career paths and mobility in the Swedish hospitality sector

ABSTRACT

How career paths are interpreted and conceptualised by hospitality workers and industry representatives remains underexplored in current literature. In this paper, we highlight and discuss sector-specific and contextual factors that influence the possibility of establishing a career within the Swedish hospitality sector. The paper uses interviews with hotel managers, who describe and discuss motivations and choices made throughout their own careers and interviews with young (former) seasonal hospitality workers who describe and reflect on their future plans and work-life experience. Additional data are derived through observations at national seminars and meetings for representatives from the Swedish tourism and hospitality industry, where issues of competence and careers were discussed. The findings indicate that the shaping of career paths within the hospitality sector is influenced by two normative and discursively produced ‘truths’ about career paths in the hospitality sector: the importance of internal knowledge transfer and the importance of high mobility. These narratives impose expectations on individuals to be mobile, to change jobs frequently and to work their way from the bottom-up within the industry, and are based on a presumption of a diversified and dense local hospitality labour market. However, since the conditions are different due to contextual, geographical features of labour market size and structure, attractiveness of places, etc., these expectations are difficult to fulfil in places other than in larger urban areas. These normative assumptions of what a successful hospitality career is also have consequences for the development of the hospitality sector as external influences of competence from other sectors and higher education are not seen as valuable, which makes the sector self-contained and not open to external, potentially innovative knowledge.     

Children's agency and Islam: unexpected paths to solidarity

This ethnographic study analyzes the experiences of Palestinian children's agency of religion and its manifestation in religion as resistance while it is fighting the globalized hegemony. Children's agency of religion as resistance is cultivated within the debate of Islamist movements and the evolution of Palestinian national identity while it serves as a call for global solidarity. It is this creative construct of agency of religion that transcends borders and distinguishes itself from the old generation method of resistance. The differences between generations on this construct, as described by children's agency and their ability to transform, is constructed by particular meanings of Islamist symbols and rejects the assumption that children's roles are defined. The agency of religion as resistance evolves as the role of religion in national discourse is deliberated in secularism and sectarianism. In 2005/2006, I was awarded the Rockefeller Fellowship in the Anthropology Department of Johns Hopkins University. The award was for my work on children's political socialization in the Middle East. I also have been active with international studies: in 2009, I collaborated with the Children's Rights Unit, Institut Universitaire Kurt Bösch, Switzerland on the research project, Living Rights: Theorizing Children's Rights in International Development. I am serving as research member on the Joint Learning Initiative on Children and Ethnic Diversity (JLICED), Division of Children's Rights. My work has been published in the Journal of Qualitative Inquiry, Childhood, Children's Geographies, Journal of Mix Method Research and others. View all notes     

Regional agency and constitution of new paths: a study of agency in early formation of new paths on the west coast of Norway

ABSTRACT

This article analyses regional agency in the early phases of new path constitution. We argue that the early stages of new path constitution can be explained by both structural factors and the strong presence of agency. With a specific focus on agency, this article contributes to the literature by providing a study of the role of agency at different stages of path constitution. The study shows that two types of agency operate together. Public policy agency is carried out through a common thrust for policy tools that can enhance the room to manoeuvre together. In addition, strong entrepreneurial agency functions as a locomotive for other firms which are important trigger points, and pushes the process forward. These two forms of agency need to be interrelated to constitute new paths.     

Regional paths towards Europe 2020 targets: a spatial approach

Europe 2020 is a 10-year EU strategy, promoting smart, sustainable and inclusive growth. Despite ambitious goals, its spatially blinded approach might seriously threaten its success. Actually, large territorial disparities still affect the EU, being the basis for a strong EU-wide cohesion policy and suggesting a general re-framing of sectoral policies on a regional basis. In this respect, the paper tackles the issue of regional disparities in achieving Europe 2020 Strategy targets. As the Strategy involves different targets, principal component analysis is applied to disentangle Europe 2020 domains and to describe major differences in EU-27 NUTS 2 regional performances. In particular, two components are returned: high-employment inclusive growth and smart growth. Territorial patterns of both components are analysed, by jointly considering some geographical features that may affect them. Both a rural and a spatial effect occur: rural and remote regions show poor performances whilst the presence of spatial autocorrelation may actually lock-in negative outcomes. When considering urban rural divides, also within-regions disparities matter. Results strengthen the idea that Europe 2020, as other sectoral policies, should be translated into a regional setting according to a place-based approach: although requiring large efforts, this represents the only way to fully achieve its own targets.     

VHF propagation modes within ionospheric waveguides

A three dimensional waveguide model of VHF ducting has been developed. The waveguide is aligned along the Earth's magnetic field and has an elliptical cross-section which, based on observations of ionospheric bubble irregularities, is taken to have axes of 10–100 km. Rays propagating to the conjugate hemisphere via the duct undergo relatively few reflections at the duct walls (typically 3–20). Consequently the waveguides are not fully excited and significant power is transmitted by modes which are not fully trapped. A complete analysis of the propagation characteristics of such ducts requires the consideration of trapped and leaky modes, focusing and tunnelling. The cross-section of the guide is defined by specifying the vertical and East-West horizontal axes at the apex of the guide (magnetic equator). Comparison of cases with the same vertical axis shows that, when the vertical axis is larger than the East-West axis, the curvature on the upper surface of the guide is consequently increased and tunnelling becomes more important. On the other hand, when the vertical axis is the smaller, focusing is greater and leaky rays become increasingly important. In some models the region of highest power in the conjugate hemisphere is due almost entirely to rays which have suffered some leakage. Obviously non-trapped modes need to be considered when attempting to explain phenomena such as trans-equatorial propagation at VHF.