Oblique ordinary mode propagation in the magnetospheric plasma

An approximate formula is obtained for ordinary mode refractive index for the case of almost perpendicular propagation in a hot anisotropic plasma with a loss cone. It is pointed out that the influence of electron finite temperature on wave propagation is stronger when the wave frequency is close to the first two harmonics of the electron gyrofrequency. Ordinary mode energy focusing in the direction perpendicular to the magnetic field can occur only in those regions of the magnetosphere, where the electron gyrofrequency is close to the electron plasma frequency. Ordinary mode waves are usually trapped in the vicinity of the magnetospheric equator and so their energy can be concentrated in this region.     

The magnetopause: microstructure and interaction with magnetospheric plasma

The microscopic properties of the magnetopause are reviewed in relation to the more general problems of the topology of the magnetosphere and the physical processes involved in magnetospheric dynamics. Studies of charged-particle trajectories in idealized magnetic fields have provided some physical insight into the microstructure of the magnetopause; this aspect of the subject is surveyed and the various idealizations and simplifications involved in the theoretical models are discussed critically. Results obtained using the microscopic approach based on charged-particle trajectories are compared and contrasted with the corresponding results obtained using the macroscopic approach based on hydromagnetics and gas-dynamics. An assessment is made of the importance of the interplanetary magnetic field and of its likely influence on the microstructure and physical properties of the magnetopause. The magnitude of any polarization electric field at the magnetopause depends on the presence of highly-conducting magnetospheric and ionospheric plasmas that permit field-aligned currents to flow between the magnetopause and the polar-cap ionosphere: this process may be complicated, however, by anomalous resistivity of the plasma in the polar cusps (clefts). Equivalent electric circuits are used to study such field-aligned currents, the possible penetration of a time-varying interplanetary electric field into the magnetotail, and the erosion of the dayside magnetosphere. It is concluded that the microstructure of the magnetopause can no longer be considered in isolation, but must now be regarded as an inseparable part of the wider problem of magnetospheric dynamics.     

Oblique HF radar studies of plasma instabilities in the equatorial electrojet in Africa

While the equatorial ionosphere was regularly investigated in South America by radar technique and a number of very interesting phenomena detected and associated with plasma instabilities, results in the other part of the world along the magnetic equator were relatively few. The preliminary results of new African experiments are presented. The experimental procedures and equipment and the first results at a.frequency of 21.3 MHz are described. The two types of instabilities previously detected at Jicamarca are regularly observed at 21.3 MHz and their characteristics are described in relation with different theories about plasma instabilities.     

Recent advances in magnetospheric substorm research

More than two decades of magnetospheric exploration have led to a reasonably clear morphological picture of geomagnetic substorms, which is often summarized in terms of the near-Earth neutral line (NENL) model of substorms. Although this qualitative theory is quite comprehensive and explains a great many observations, it is hard pressed to explain both recent observations of consistently earthward flow within 19 R_E and also the prompt onset of magnetic turbulence at 8 R_E at the time of substorm onset. Other theories have recently been proposed which tend to be more quantitative, but which explain a more limited number of substorm observations. The challenge seems to be to understand the essential physics of these various quantitative theories and integrate them into a larger structure such as is provided by the near-Earth neutral line model.     

Analytic calculation of the ordinary (O) and extraordinary (X) mode nose frequencies on oblique ionograms

On oblique ionograms, the maximum frequencies of the ordinary and extraordinary modes are referred to as nose frequencies. The difference in the nose frequencies depends on parameters such as the length of the propagation circuit and the direction of propagation. In this paper, the difference in nose frequencies is studied using the frequency scaling technique of Bennettet at. [(1991) Appl. Comput. Electromagn. Soc. Jl6, 192]. For long paths, an explicit formula is obtained which gives the difference approximately as a function of the local magnetic dip and azimuth of propagation at the ray mid point. For shorter paths, it is shown how analytic ray tracing can be used to determine the difference.     

Non-relativistic and relativistic approaches to the problem of plasma wave propagation

When using the approximate expression for different wave refractive indices derived by Sazhin we outlined those values of plasma parameters and wave frequencies for which cold and non-relativistic plasma approximations are valid. For R and O waves the latter approximation is valid when the wave frequency is close to the electron gyrofrequency; for the X wave it is valid when the wave frequency is close to the doubled electron gyrofrequency.     

Electric field generation at the magnetospheric boundary for northward IMF

We discuss three different processes which generate electric fields at the magnetopause during northward interplanetary magnetic field (IMF) conditions. These are (1) Petschek-type magnetic field reconnection, (2) magnetic field diffusion, and (3) viscous-like interaction resulting from the Kelvin-Helmholtz instability. For northward IMF all three processes lead to the formation of a boundary layer on closed magnetic field lines adjacent to the magnetospheric boundary. The thickness of the boundary layer depend on Petschek's parameter in the first case, the magnetic Reynolds number in the second case, and an effective Reynolds number in the third case. In each case coupling between the boundary layer and the ionosphere occurs via field-aligned currents. These field-aligned currents result from the penetration into the polar ionosphere of the electric field generated at the magnetospheric boundary. These currents are closed by a transverse current in the boundary layer and the associated Lorentz force causes a decrease of the kinetic energy of the solar wind plasma inside the boundary layer. As a result of this velocity decrease the thickness of the boundary layer increases on both flanks of the magnetosphere near the equatorial plane. The convergence of the boundary layer on the dawn and dusk sides leads to antisunward plasma flow in the magnetospheric tail.     

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.     

Whistler-mode propagation: results of model calculations for an inhomogeneous plasma

Waveforms computed using the new whistler model derived from Maxwell's equations were analysed. In the calculations, realistic model values for magnetospheric parameters were used. The results accurately described whistler-mode propagation in the magnetosphere and provide explanations for some features exhibited by real observed whistlers when they are analysed. In particular, solutions of the exact full-wave whistler model can explain the whistler fine structure, and may be used to develop a more accurate (matched filtering) fine-structure analysis method.     

Magnetic field of the magnetospheric ring current and its dynamics during magnetic storms

This review examines models existing in the literature which describe the magnetic field produced by the ring current (DR) at the Earth's surface based on the energy balance equation. The parameters of this equation, the injection function F and decay parameter τ are considered to depend on parameters of the interplanetary medium and the DR intensity. The existing models are shown to be able to describe the DR variations with sufficient accuracy (r.m.s. deviation δ between the experimental and modelled values of DR for 170 magnetic storms is 5 < δ < 15 nT and the correlation coefficient between the two is 0.85 <r<1). The models describe that part of the geomagnetic field variation at low latitudes during a magnetic storm that is controlled by the geoeffective characteristics of the interplanetary medium and which thus responds immediately to its variations (the driven part).The values of τ are significantly less during the main phase of a magnetic storm than during the recovery phase. This reflects the difference in the main mechanisms of ion loss from the ring current during the two phases of the storm. These are the interaction of ions with hydromagnetic waves during the main phase of the storm with its intervals of intense plasma injection into the inner magnetosphere and charge exchange with the cold hydrogen geocorona during the recovery phase.     

Auroral radio absorption as an indicator of magnetospheric electrons and of conditions in the disturbed auroral D-region

In a previous paper we demonstrated a method by which the auroral radio absorption measured with a riometer can be predicted from energetic electron measurements at geosynchronous orbit. The present paper enquires to what extent the process can be inverted: what levels of magnetospheric electron flux, and of D-region production rate, electron density and incremental absorption, are predicted by a given measurement of radio absorption and what reliance can be placed on such predictions?Using data from 45 precipitation features recorded with riometers in Scandinavia and at geosynchronous orbit with GEOS-2, it is shown that electron fluxes in the ranges 20–40,40–80 and 80–160 keV increase with increasing absorption and can be predicted to better than 50% for absorption events of 2 dB or greater. Electrons above 160 keV show little or no correlation with absorption. D-region production rates and electron densities can be predicted to within factors of 2 and √2, respectively.It is more difficult to specify the height of the absorbing region because of uncertainly in the profile of the effective recombination coefficient. Having regard to other data, an α_eff profile is proposed which satisfies rocket and incoherent scatter data as well as the present calculations. It is shown that any day-night variation in auroral absorption is associated with a change of spectrum rather than a change of recombination coefficient.     

The man behind the syndrome: Argyll Robertson,Scotland's ambassador extraordinary in the realm of ophthalmology

Abstract

The aim of this study is to find out whether bromide was able to cause conversion of epilepsy to psychosis i.e., so‐called paradoxical normalization such as has been seen in treatment with modern antiepileptic drugs. Spontaneous conversion has been known for three hundred years. Locock introduced bromide in the treatment of epilepsy in 1857. Belgrave wrote in 1868 on its effect on epileptic attacks and concommitant insanity. In 1868 Holm observed reduction of the frequency of seizures at the same time as psychotic symptoms or just dysphoria. In 1875 Voisin described a dose‐dependent intoxication with psychosis and/or neurological signs. Stark in 1875 and Bannister in 1881 were the first to clearly describe the antagonism between epileptic seizures and psychotic symptoms, an antagonism or conversion described by many authors, both in cases with high and low dosage, and with and without intoxication. Thus, the title of this paper should be answered in the affirmative.

Bromide has been used as a sedative and has rarely caused intoxication. Thus the presence of epilepsy is not a condition for the development of bromide intoxication. A case with epilepsy and fatal massive bromide intoxication is reported. It is discussed whether the pathological findings give support to Wolf's hypothesis of latent epileptic activity in subcortical pathways during “normalization”;.     

On the problem of a connection between ozone dynamics at high latitudes and magnetospheric processes

Two data sets of ozone density measurements over a wide latitudinal range in the Arctic during summer and winter seasons arc presented. It is shown that geophysical effects manifest themselves in the O₃ dynamics in the high latitude region under various circumstances. Therefore a type of total ozone content diurnal variation is a distinctive feature in the auroral oval as well as the polar cap and must be taken into account in any full model of ozone dynamics in the polar regions.     

Mechanisms and time-scales of the magnetospheric response to the interplanetary magnetic field changes during the 8 May 1986 substorm

On 8 May 1986, between 1113 and 1600 UT, an isolated magnetospheric substorm was observed, during which the AE-index exceeded 700 nT (CDAW 9E event). Three available sets of measurements (a) of the solar-wind parameters (IMP-8 satellite), (b) of the magnetotail energy flux (ISEE-1 spacecraft), and (c) of ground magnetic observatories, allowed us to make a detailed study of the overall magnetospheric response to changes of the interplanetary magnetic field (IMF) direction, during this event of weak solar-wind coupling.In order to study the mechanisms and time-delays of the magnetospheric response to the abrupt increase of the solar-wind energy input, we have evaluated the total magnetospheric energy output U_T following two different methods: (a) Akasofu's method, taking the ring current decay time τ_R constant, and (b) Vasyliunas' method where the values of u_t are independent of the solar-wind energy input as determined from the epsilon parameter. Both methods suggest that the driven system has been considerably developed during this substorm, while an unloading event has been superposed at the expansion onset.     

From the familiar to the extraordinary: local residents' perceptions of risk when living with nuclear power in the UK

Nearly two decades since the last nuclear power station was built and began operating in the UK, nuclear energy is firmly back on the political agenda domestically and elsewhere in the world. Yet since the 1980s, little research has investigated perceptions of nuclear power in the UK, particularly those of communities living in very close proximity to such facilities. Using biographical narrative interviews (n = 61), we explore how local residents living close to two nuclear power stations in the UK (Bradwell, Essex and Oldbury, South Gloucestershire) have come to view their local facility. We reveal how the power station is constructed through processes of familiarisation and/or the normalisation/normification of risk as part of everyday life; how this ordinariness is juxtaposed with moments of extraordinariness in which, due to direct and mediated events, the power station is reframed as a risk issue; and how risk awareness is associated with moments of anxiety which ebb and flow through our interviewees' lives. We conclude that biographical experiences dynamically unfolding through space and time can be interrupted by risk events (mediated and direct, real and symbolic, nuclear and non-nuclear) to disrupt the usually taken-for-granted ordinariness of a power station's presence in a particular locality. Our findings suggest that those involved in debate about new nuclear build must be sensitive to the heterogeneity of the extraordinary in nuclear affairs and the importance of socio-cultural histories of place.     

The propagation of the mesospheric two-day wave in the southern hemisphere

The results of an analysis of mesospheric wind data collected simultaneously at Grahamstown (South Africa) and Adelaide (South Australia) during the summer appearances of the quasi-two-day wave over a period of eight years are presented and discussed. It is concluded that the apparent zonal wave-number k which characterises the westward travelling wave is significantly less than the value of 3 suggested by current theories. Differences in local conditions and/or observing techniques are found to be unlikely causes of the discrepancy. It is shown that these results, as well as certain global features observed by satellite, could arise as a result of the superposition of modes with different k but similar frequencies.     

Theoretical study of propagation of short periodic gravity waves within the thermosphere. Application to the plasma line measurement and to a Faraday rotation experiment

The harmonic analysis of the plasma frequency fluctuations obtained with the plasma line experiment at St. Santin shows the existence of a noise of fluctuations for periods below 20 min. The main feature of this noise is to present a cut off low period which is essentially variable. A theoretical study of the propagation of short periodic gravity waves within a realistic thermosphere shows that the main parameter governing the position of the cut off frequency is the wind profile. The same theoretical study shows that the gravity waves of period between ¦16, 20¦min can propagate essentially during the day and the waves of period between ¦10, 13¦min propagate during the night. This conclusion is in agreement with the results of a Faraday rotation experiment.