Auroral electrons

Satellite and rocket measurements of auroral electrons (which have been made since Brown's (1966) and Pfister's (1967) papers have appeared) are reviewed, and the salient characteristics of auroral electrons which emerge from all types of measurements are summarized. Effects of the atmosphere on the energy distribution of electron fluxes are discussed. Ionization rates associated with typical fluxes are derived. Observable effects produced in the atmosphere and the fate of auroral electrons are briefly described.This paper does not discuss the role of auroral protons (or particles). A recent review on the subject has been given by Eather (1967).     

We think we know where we are,but can anyone tell us where we are going? Has the European Union lost its way?

Using the various problems and delays in the Galileo satellite navigation programme as a metaphor for European leaders' incompetence and complacency in a wide range of other important fields, this viewpoint bemoans the lack of direction in both the European project and its space policy, the result of growing state nationalism and a neoliberal approach that has left the continent at the mercy of globalisation.     

Attempt to identify a source mechanism of Mercury’s sodium exosphere by a spectrometer using Fabry–Perot etalon

The Mercury’s Sodium Atmosphere Spectral Imager (MSASI) on BepiColombo (BC) will address a range of fundamental scientific questions pertaining to Mercury’s exosphere. The measurements will provide new information on regolith–exosphere–magnetosphere coupling as well as new understanding of the dynamics governing the exosphere bounded by the planetary surface, the solar wind and interplanetary space. MSASI is a high-dispersion visible spectrometer working in the spectral range around sodium D2 emission (589 nm). A tandem Fabry–Perot etalon is used to achieve a compact design. We presents a design of the spectral analyzer using Fabry–Perot interferometer. We conclude that: (1) The MSASI optical design is practical and can be implemented without new or critical technology developments; (2) The thermally-tuned etalon design is based on concepts, designs and materials that have good space heritage.     

In situ and remote sensing of thermospheric winds during the energy budget campaign

This paper summarizes the dynamical information obtained in the lower thermosphere during the Energy Budget Campaign, by three experimental techniques: rocket-borne falling spheres instrumented with accelerometers and Tri-Methyl-Aluminium (TMA) trails, and from a ground-based Fabry-Perot interferometer. Winds of 200–400 m/sec, accelerated by the momentum and energy inputs from the magnetosphere, were observed during the ‘B’ and ‘A2’ salvos (15/16 Nov 1980 and 30 Nov/1 Dec resp.), with perturbations as low as 100 km altitude during the ‘B’ salvo. A global model has been used to simulate the wide-scale consequences of these disturbances, and to aid estimation of the integrated energy and momentum inputs.     

Magnetic Field Observations of Transient Events at Ulysses, 1996–2000

During the years 1996–2000 solar activity has been gradually rising and is now close to maximum. At the same time the Ulysses spacecraft has performed a north to south traverse of the low latitude regions of the heliosphere and is now once again travelling through high southerly latitudes. We show some examples and report on the occurence rates of transient solar wind disturbances which have been identified by their magnetic field signatures. ‘Magnetic clouds’ remain more common at low (compared to high) latitudes despite the rise in solar activity. However, more events were observed at high latitudes than at solar minimum. This revised version was published online in August 2006 with corrections to the Cover Date.     

Wind structure and small-scale wind variability in the stratosphere and mesosphere during the November 1980 energy budget campaign

Between November 6 and December 1, 1980, a series of rocket observations obtained from two sites in northern Scandinavia as part of the Energy Budget Campaign indicated that significant vertical and temporal changes in the wind structure were present and were noted to coincide with different geomagnetic conditions, i.e., quiet and enhanced. This series of observations represents for the first time the largest amount of data ever gathered at high latitudes over such a short interval of time. It is observed that prior to November 16, the meridional wind component above 60 kilometers was found to be positive (southerly) while the magnitude of the zonal wind component increased with altitude. After November 16 the meridional component became negative (northerly) and the magnitude of the zonal wind component was noted to decrease with altitude. Time-sections of the perturbations of the zonal wind show the presence of vertically propagating waves which suggest gravity wave activity. These waves increase in wavelength from 3–4 kilometers near 40 kilometers to over 12 kilometers near 80 kilometers. The observational techniques employed at Andoya, Norway, and ESRANGE in Sweden, consisted of chaff foil, chemical trails, inflatable spheres, and parachutes.     

Optical observations of ion tail structures and velocity flows in comet Halley during the period of the five spacecraft encounters

Observations of the distribution and evolution of a number of the major constituents of the neutral coma (CN, C₂, CH, O, H, Na) of Comet Halley were made during two observing periods, each of 3 weeks duration, from the Table Mountain Observatory, California. The first period was pre-perihelion, in late November/December 1985. The second period, from Feb 28 to March 22 1986, covered the five close spacecraft encounters with Halley, and when ICE flew some 20 M Km upstream of Halley. Sodium emission was recorded in early Dec 1985 from the near-nuclear region at a heliocentric distance of 1.4 AU, an observation confirmed with the UCL Doppler Imaging system. The CN coma could be detected to an outer diameter of more than 4M Km in Dec 1985, and 5 – 6M Km in early March 1986, allowing the production of heavy cometary pick-up ions to be estimated. Observations of the cometary ion coma (H₂O⁺ and CO⁺ ions) showed considerable variability from day to day, particularly during the period of the spacecraft encounters. These observations have been used, in conjuction with the neutral coma data, to map the flow field of cometary ions. In early Dec. 1985, Halley developed a traditional “type I” ion tail, which persisted until late April 1986. It has also been possible to evaluate the ion flow fields within the narrow core of the ion tail, and in the surrounding diffuse, low density, regions populated by pick-up and extracted cometary ions, and by slowed solar wind ions. Tail disconnection events were observed on several occasions, particularly between the VEGA 2 and GIOTTO encounters, and with a highly spectacular event on March 19 1986.     

Stars and Stellar Systems at z > 5: Implications for Structure Formation and Nucleosynthesis

Enough UV radiation was generated before z = 5 to have ionized the intergalactic medium. If this comes from stars (probably aggregated in systems of subgalactic scale), one straightforwardly calculates that the associated nucleosynthesis would be sufficient to produce a universal abundance of order 1 percent of solar. The first pre-galaxies may eventually be detectable by their direct UV emission, with characteristic spectral features at Lyman alpha; high-z supernovae may also be detectable. Other probes of the IGM beyond z = 5, and of the epochs of reheating and reionization, are discussed, along with possible links between the diffusion of pregalactic metals and the origin of magnetic fields.     

Semi-empirical model of middle atmosphere wind from the ground to the lower thermosphere

During recent years, special attention has been paid to understanding the background circulation of the middle atmosphere. Particularly in the mesosphere/lower thermosphere (MLT) region, this has involved including data from a range of new radar measurements. It has also involved the comparison of existing empirical middle atmosphere wind models, such as CIRA-86 and HWM-93 to the new data. This has led to the construction of empirical models of MLT winds such as the Global Empirical Wind Model (GEWM). Further investigations are aimed at the construction of new empirical and semi-empirical wind models of the entire middle atmosphere including these new experimental results. The results of a new wind climatology (0–100 km) are presented here, based upon the GEWM, a reanalysis of stratospheric data, and a numerical model which is used to fill the gap between data from the stratospheric and MLT regions.