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Apparent discrepancy is discussed between the height profiles of atmospheric conductivity derived from Schumann resonance parameters in the Earth-ionosphere cavity and using the model of the DC global atmospheric electric circuit. The issue is resolved by creating a hybrid profile of these two profiles. Close to the ground, where the resistance of the atmosphere is largest, the properties of the DC global model exert the greatest influence, whereas in the middle atmosphere, at heights between 40 and 100 km, the full wave computations show that the AC results are the more crucial. This globally averaged hybrid profile harmonizes the AC and DC conductivity data, and it might be important for future studies.

The exhaust emissions from civil subsonic aircraft at cruise altitude are important man-made sources that pollute the upper troposphere and the lower stratosphere (8-12 km). The formation of NO y species from NO x, both before and after the exit nozzle, have created increasing environmental concerns. Flight histories of Boeing 747-400 aircraft during the cruise stage between selected city pairs have been simulated using a computer program developed at Cranfield University. The passive distribution of NO x and HNO3 is calculated using the UGAMP three-dimensional chemical transport model. The sink of NO x, which is HNO3, is parameterized using an exponential decay process with an altitude-dependent lifetime. The model also includes transport by advection, vertical diffusion and convection. These simulations for January and July are analysed in terms of the resulting mean volume mixing ratios for both NO x and HNO3.

The most significant man-made sources of pollution of the higher troposphere and lower stratosphere are exhaust emissions from civil subsonic aircraft at cruise altitude (8–12 km). This paper examines such issues by computational modelling of Boeing 747-400 flights during their cruise phase between selected city pairs, for example London to Tokyo. The engine performance, exhaust pollutant prediction, and detailed flight history analysis effects of different Mach numbers and of increasing the cruise altitude from 9.8 to 12.1 km during the flight rather than staying at a constant cruise altitude of 10.5 km are studied in detail. To minimise the overall effects of atmospheric pollution, a Mach number of 0.85 and increasing altitude is the favoured cruise technique.

A model is proposed for blue jets [Sentman and Wescott, 1995; Wescott et al., 1995a], which explains their dynamics, in particular the jet vertical velocity of about 100 km/s, the terminal altitudes of about 40–50 km, and the competitive occurrence of blue jets and the recently discovered blue starters [Wescott et al., 1995b]. A blue jet is considered to be formed by an attachment-controlled ionizing wave, which moves upward via an electron avalanche in the wavefront due to the mainly vertical, downward directed quasi-electrostatic field, caused by the extraordinarily large (>100 C) charge transfer in a high-altitude intracloud discharge or in a positive cloud-to-ground discharge with a long continuing current.

An overview of the subject of space plasma physics is attempted. This encompasses a discussion of various ground-based and satellite studies of the near-Earth space environment, with its marked temporal and spatial variations, theoretical investigations, and numerical simulations. The important distinction is drawn between passive studies of elements of the natural system, aimed at the difficult task of understanding the self-consistent evolution of some natural processes, and active investigations, which either probe or modify natural processes, in order to improve understanding of cause and effect (e.g. of energy transformations) within the system. Linear, nonlinear, and chaotic processes can occur. Attention is paid to: The approach adopted is to place these special topics in the context of the Solar Terrestrial Energy Program (STEP) of ICSU's SCOSTEP. Finally, mention is made of some benefits to humanity of studies of space plasma physics phenomena.

An analog electrical engineering model of the global atmospheric electric circuit has been constructed with thunderstorms and electrified rain clouds as generators. This has been used to estimate changes to the ionospheric potential (∼ 250kV) due to lightning and sprites. It has been found that this change is: (i) +3.7V for a negative cloud-to-ground (CG) discharge having a typical return stroke current of 30 kA, (ii) −43V for a typical positive CG discharge with a 2kA continuing current lasting 90 ms, (iii) −2.3V for an intra-cloud discharge, and (iv) −1.0V for a sprite.

The Solar Terrestrial Energy Programme (STEP) aims to improve our general understanding of how mass, energy and momentum are transferred between the various regions that form the Solar Terrestrial environment. STEP began in 1990 and will continue until 1997, during which time a number of major new spacecraft and ground-based projects will become operational. Six Working Groups form the basis of STEP, covering topics such as the Sun as a source of energy and disturbance, energy and mass transfer through the interplanetary medium and the magnetosphere-ionosphere system, ionosphere-thermosphere coupling and response to energy and momentum inputs, middle atmosphere responses to forcing from above and below, solar variability effects in the human environment, and informatics. A Royal Astronomical Society Geophysics Discussion meeting took place in March 1992 to draw to the attention of UK scientists the diverse nature of STEP and the opportunities offered by STEP. This paper consists of individual sections prepared by the speakers at the meeting and which cover most of the STEP Working Group topics. The main aims of each section are to provide a “benchmark” for the present status of the research area and to look ahead to the possible contributions that UK scientists can make during STEP.

The work considers the highly anisotropic electron distribution functions observed by Bell and co-workers at Stanford in the magnetosphere. IOt is maintained that Bells' observations provide evidence for the existence of step like deformations in electron distribution function, and that his observations may be due to such steps. The origin of such steps at the top of hiss band emissions is explained, and the implications for triggering of emissions and chorus is explained.

We discuss the fair weather atmospheric electric field signatures of three major solar energetic charged particle events which occurred in on 15 April 2001, 18 April and 4 November, and their causative solar flares/coronal mass ejections (SF/CMEs). Only the 15 April 2001 shows clear evidence for Ez variation associated to SF/CME events and the other two events may support this hypothesis as well although for them the meteorological data were not available. All three events seem to be associated with relativistic solar protons (i.e. protons with energies >450 MeV) of the Ground Level Event (GLE) type. The study presents data on variations of the vertical component of the atmospheric electric field (Ez) measured at the auroral station Apatity (geomagnetic latitude: 63.8°, the polar cap station Vostok (geomagnetic latitude: −89.3°) and the middle latitude stations Voyeikovo (geomagnetic latitude: 56.1°) and Nagycenk (geomagnetic latitude: 47.2°). A significant disturbance in the atmospheric electric field is sometimes observed close to the time of the causative solar flare; the beginning of the electric field perturbation at Apatity is detected one or two hours before the flare onset and the GLE onset. Atmospheric electric field records at Vostok and Voyeikovo show a similar disturbance at the same time for the 15 April 2001 event. Some mechanisms responsible for the electric field perturbations are considered.

The polar regions are unique laboratories for carrying out research on both the atmosphere and the near-Earth space environment. The relatively undisturbed conditions help us explore phenomena like the greenhouse effect and the springtime Antarctic ozone depletion, the so-called ozone hole. Further out, uv and x-radiation from the Sun produce the Earth s Ionosphere, vital for man s communication network. Yet satellite and polar research is showing us how events on the Sun can adversely affect this near-Earth space environment.

The principles of operation of satellite navigation systems1 may be outlined as follows. Earth-orbiting satellites, carrying extremely accurate atomic clocks, broadcast time information at the L1 frequency (1.5754 GHz) and L2 frequency (1.2276 GHz). A sensitive receiver (e.g., aboard an aircraft) picking up these radio signals (~10−16 W received power) from four different Global Positioning System (GPS) satellites measures four pseudo-ranges and, by triangulation, calculates the aircraft’s position (in three dimensions) and its velocity. The performance of such a positioning system — with its accurate time reference — may be enhanced, or “augmented”, in various ways by using additional radio sources, either in space or on the ground.

Space weather is a multi-disciplinary subject that relies on dedicated spacecraft constantly monitoring the various relevant regions of space. The Sun is of special interest; continuous monitoring of definitive solar wind parameters upstream of the Earth is required, as are timely warnings of solar flares, coronal mass ejections and other extreme solar events. Measurements by instruments on small spacecraft would most cost-effectively provide continuous coverage of the various physical phenomena that cause undesirable space disturbances.

[1] We study the amplification of ducted whistler-mode waves in the Earth’s magnetosphere by the cyclotron instability for different types of energetic electron distributions in velocity space. Particular attention is paid to the comparison between cases of smooth distribution functions and those with sharp gradients (‘‘steps’’) in velocity space, which arise naturally owing to interactions with noise-like VLF emissions. We show that step-like features greatly favor the amplification of whistler-mode waves propagating along the Earth’s magnetic field line and hence the generation of narrowband VLF emissions even if the electron anisotropy is only moderate. The results obtained are discussed in light of observations of discrete VLF emissions from the magnetosphere, in particular those of Bell et al. [2000]. INDEX TERMS: 2720 Magnetospheric Physics: Energetic particles, trapped; 2730 Magnetospheric Physics: Magnetosphere—inner; 0654 Electromagnetics: Plasmas; 2772 Magnetospheric Physics: Plasma waves and instabilities; KEYWORDS: whistlers, amplification, anisotropic, electrons, step-like, chorus

L'article est focalise sur les proprietes de la depletion printaniere de l'ozone en Antarctique et sur l'interrelation de la dynamique atmospherique, du rayonnement et de la chimie qui peut expliquer ces proprietes. Quelques consequences du trou d'ozone sont considerees

The topic of the whistler precursor, a discrete VLF emission which is occasionally observed to precede a whistler, is briefly reviewed. An analysis of some observations of precursors is presented, and two new mechanisms for the generation of precursors are described. It is shown that a mechanism in which two frequency components of a whistler, having the same group delay, interact to trigger a precursor at the difference of the frequencies does not predict results which agree well with observations. A mechanism in which part of the energy from the causative lightning stroke travels in an unducted mode, undergoing one magnetospheric reflection and refraction from the inner edge of the plasmapause, arriving in the equatorial plane with its wave vector parallel to the geomagnetic field, predicts results which are in good agreement with experimental observations. This method is compared with the model of Dowden (1972).

The three-spacecraft AMPTE Mission was due to commence in August 1984. The purpose of these 'active' experiments was firstly to release lithium into the solar wind and to use the lithium ions, formed by photoionisation, as 'test particles' to investigate their crossing of the bow shock, their entry into the magnetosphere and subsequent energisation. Secondly, it was to release barium in the dawn magnetosheath to create an artificial comet. Thirdly, it was to inject both lithium and barium into the tail of the magnetosphere to study plasma convection. Observations were to be made both on the spacecraft and from the ground. These would provide information on the plasma physics of the natural plasma environment of the Earth and also of the formation and evolution of an expanding diamagnetic cavity. Particular attention was to be paid to the various plasma instabilities and wave phenomena anticipated in these experiments, and to the natural waves which would be observed.