Electron temperature variations during solar-maximum conditions (200–3500 km)

The electron temperature variations are investigated above Arecibo, Jicamarca, Millstone Hill, St. Santin and a polar area—located at the meridian of Millstone Hill. The data analyzed represent quiet geomagnetic conditions (Kp ≤ 3) during a solar maximum (1967–1970). Between 200 and 600 km the electron temperature data stem from incoherent scatter measurements and above 600 km from the ISIS-1 observations. A simple analytical model which includes Fourier terms and cubic splines (for approximating the height dependence of the coefficients) describes the diurnal and seasonal pattern of the electron temperature in the altitude interval 200–3500 km. Three height regions are particularly striking, i.e. near 200 km where the diurnal variations show a sinusoidal pattern, the altitude interval up to approximately 1000 km which exhibits strong temperature gradients and a complex diurnal and seasonal structure, and the upper region beyond 1000 km which reflects again sinusoidal pattern but with a very pronounced latitudinal dependence.     

THE SAN JUAN CAPISTRANO METEORITE

The San Juan Capistrano chondrite fell on 15 March 1973; the total recovered mass was 56 g. Electron microprobe, chemical and petrographic studies show it to be a member of the H group and of petrologic type 6. Rare gas studies show that only minor radiogenic gas loss has occurred and yield a K-Ar age of 4.6 × 10⁹ years and a Kr-Kr exposure age of 29 × 10⁶ years.     

On making radio contact with extraterrestrial civilizations

The problem of, attempting to make radio contact, with other technological civilizations is examined. It is argued that there are few (perhaps indeed no) omnidirectional radio beacons in the Galaxy primarily because any such beacon, to be effective, would have to be designed for a call-response time of at least some 10⁴ years, which is much too long to be likely to be acceptable to governments. A consequence, is that any search program by us would have little chance of detecting incoming signals.Paper dedicated to Professor Hannes Alfvén on the occasion of his 70th birthday, 30th May, 1978.     

Equatorial scintillation

Equatorial scintillations have been observed at Legon, Ghana for nearly 20 yr. The occurrence characteristics of the scintillations are reviewed, and the physical characteristics of the electron density irregularities summarized. A much more comprehensive summary of the seasonal variation of scintillation is given, and it is found to be remarkably similar to the variations in thermospheric temperature. Evidence for the suppression of scintillation during magnetic disturbances is given. Curves for the daily variation of the Faraday rotation angle φ are presented and their unusual post-sunset behaviour noted. It is suggested that this can be explained in terms of a theory presented by Rishbeth, in which the F region ionization moves with nearly the full velocity of the neutral atmospheric wind at night, after the E region conductivity has fallen to a relatively low value. This can account for the observed drift velocity of the irregularities. The rapid increase in the post-sunset horizontal velocity of the ionization together with the observed vertical rise, can account for the variations of φ. It is further suggested that the large gradients in the density and drift velocity of the ionization resulting from the mechanism suggested by Rishbeth give rise to the production of the observed F region irregularities in electron density which cause equatorial scintillation.     

The termination of the solar wind

It has previously been suggested that the solar wind might terminate at distances of 5 AU to 20 AU from the Sun, and that the solar wind might be drastically slowed down by charge exchange and photoionization of interstellar hydrogen atoms which approach the Sun. However, recent satellite measurements of resonantly scattered Lyman alpha radiation, together with pulsar dispersion and Faraday rotation measures, imply very small values for the interstellar hydrogen density (0.05 cm⁻³) and magnetic field strength (3 μG). As a result, the solar wind is not expected to be slowed down by more than about 30% inside the termination distance, which is expected to be about 100 AU.     

Surface heat fluxes and subsurface heat content at a site over the southeastern Bering Sea shelf, May–July 1996

Observations from a surface mooring, in a weak-flow regime over the southeastern Bering Sea shelf, were used to derive surface heat fluxes for the period May–July 1996. Changes in heat content of the water column also were determined from subsurface temperature measurements. Agreement of net surface heat flux and change in heat content was within 2%. This result provides additional evidence that heat advection and diffusion are small in this region.     

The effect of recreational impacts on soil and vegetation of stabilised Coastal Dunes in the Sharon Park, Israel

Coastal sand dunes are considered among the most susceptible habitats to recreational use. The aim of this study was to monitor the impact of visitor use on soil and annual plants on long-established trails in the stabilised coastal dunes of the Sharon Park, Israel. The results indicate that:

1. The vegetation cover, height and species richness and diversity, as well as soil organic matter content were lower on trails subjected to high visitor use than that on trails under low use. However, soil compaction and moisture on high-use trails were higher than that on low use.

2. The rate of change in each of the vegetation properties moving outwards from the centre of the trail towards the undamaged area on its margins and beyond, was higher on trails under high visitor use than on low-use trails.

3. The impact of high visitor use is localised and limited to the trail boundaries and their immediate surroundings (6 m axis perpendicular to the trails), while the effect on low-use trails is dispersed over a larger area, apparently because the trail borders are less visually defined to the visitor.

The conclusion derived from this study is that the spatial damage caused to the park by the numerous low-use trails is higher than that caused by the trails under high visitor use. Thus, there is an immediate need to reduce the number of this type of trails and to rehabilitate them.