[en] Sporadic E, or E(s) events under the main F region trough have been confirmed on the basis of ionograms from a vertical incidence ionosonde at Halley Bay, Antarctica. Analyses indicate that E(s) is frequently observable under both the equatorward and the poleward edges of the trough, as well as poleward of it. Before magnetic midnight, E(s) layers whose semithickness resembles those of the normal E layer are common, in contrast to layers seen after magnetic midnight which show the characteristics of thin E(s) layers. A possible explanation of the observed change in the E(s) layer characteristics at magnetic midnight is related to differences in the type and spectra of the precipitating particles. It is shown that the redistribution of ionization by the convection electric field may be important. 40 references

[en] The seasonal and solar cycle dependences of the ionosphere over Chatanika, Alaska, as deduced from 108 experiments conducted over the course of an 11-year period, have yielded electron concentrations, electron and ion temperatures, and line-of-sight in velocities, as functions of altitude and time. Attention is presently given to E and F region ionization. Empirical relationships are established which allow the daytime maximum E region electron concentrations to be expressed in terms of the 10.7-cm solar flux and the solar zenith angle, and also permit the expression of the daytime maximum F region electron concentration in terms of the 10.7-cm solar flux alone. The dependence of nighttime precipitation-produced ionization in both the E and F regions on solar flux and magnetic activity is noted, together with a clear distinction between summer and winter F region ionization conditions. 7 references

[en] An approximate evaluation is made of the ELF/VLF dipole moment of the polar electrojet antenna established by ionospheric heating via the use of powerful HF waves amplitude modulated with frequencies in the ELF/VLF range. The theory of reciprocity is used to determine the magnitude of the ELF/VLF waveguide excitation produced by such a dipole immersed in the ionosphere. Propagation under a series of ionospheres ranging from quiet auroral nighttime to disturbed auroral daytime is considered. 32 references

[en] Thirty-three observations using incoherent-scatter radars from stations widely separated in longitude, and measurements made with STARE and Dynamic Explorer satellites constitute the Magnetosphere-Ionosphere-Thermosphere Radar Studies (MITHRAS), conducted between May 1981 and June 1982. The experiments were designed to monitor the auroral zone and thereby improve understanding of magnetosphere-ionosphere-thermosphere interactions with emphasis on local time/universal time variations. Three experimental modes with different time resolution and spatial coverage were used (e.g., time resolution ranged from 10-45 minutes). A catalog of MITHRAS experiments is presented which includes times of observations and an indication of the magnetic activity. 31 references

[en] The ionospheric modification facility at Arecibo, Puerto Rico, has been used to study Langmuir waves excited in the lower ionosphere by a high-power HF radio wave. Measurements of HF-enhanced plasma lines have been made in the lower F region (less than 160 km altitude) and in the E region using the 430-MHz radar at Arecibo Observatory. These measurements complement observations made in the past at higher altitudes. Enhanced plasma line spectra observed in the lower F region peak at the so-called 'decay line' and contain additional spectral structure similar to that found in the upper F region. In the E region the spectra exhibit narrow peaks located at 430 MHz + or - f(HF), where f(HF) is the frequency of the modifying HF wave. While strong plasma line enhancements are commonly observed in sporadic E, only weak enhancements have been detected in the normal daytime E layer. Candidate mechanisms for the E region enhancements include the oscillating two-stream instability and direct conversion of the HF wave into Langmuir waves

[en] A solar wind-magnetosphere-ionosphere system model is proposed which is directly driven by the solar wind-magnetosphere dynamo. The dynamo feeds the Pedersen currents to the ionosphere by generating the field-aligned currents, yielding both Joule heat and ionospheric convective motion. The field-aligned currents associated with both the Pedersen and Hall currents introduce considerable complexity into this system by generating a potential drop along the geomagnetic field lines, and it is noted that the geometry of the open region at the polar cap changes drastically as the B(z) component of the IMF becomes positive

[en] Attenuation of electromagnetic waves by a random distribution of pair-correlated dielectric spheres is studied as a function of frequency and volume concentration of spheres. The main aim of this paper is to compare theoretical results obtained using a self-consistent multiple-scattering formulation and measured values of attenuation for latex spheres in water. The agreement between theory and experiment is very good

[en] Three events chosen to give a range of magnetic conditions and local times are considered in the present case studies of the equatorward movement of the main F region trough. Upon projection into the equatorial plane, the comparison of the results with theoretical predictions of the simple, 'teardrop' plasmapause model shows very good agreement for the two occasions when the level of magnetic activity remained approximately constant over the observing period. Estimates of the strength of the dawn-dusk convection electric field in the magnetosphere have accordingly been made. Suggestions are given for the improvement of empirical models which, if implemented, may increase the reliability of predictions for high frequency, transauroral radio wave communications. 23 references

[en] The long-line technique for measuring ionospheric convection was developed for use at high midlatitudes. In this study it was employed near the auroral zone (62 deg Lambda). Measurements are very comparable with those from other techniques. The convection patterns were found to be dominated by fluctuation with periods of several minutes to several hours and spatial extent greater than 500 km but less than 1500 km. The convection was quite different on quiet and on disturbed days. 6 references

[en] A guide to the whistler literature is presented, with emphasis on whistler probing of plasma structure and motions near the plasmapause. Whistler probing experiments have identified several types of variations in plasmasphere radius with local time, including (1) variations of a few tenths of an earth radius over about 20 deg longitude that appear to originate on the nightside of the earth during substorms, (2) a secondary maximum in plasmasphere radius near noon, and (3) the duskside plasmasphere bulge. A variety of remarkable, and as yet incompletely understood, VLF propagation effects occur in the vicinity of the plasmapause, including a decrease in received whistler activity outside the boundary and unusual propagation features such as echoing above the half-equatorial gyrofrequency on paths just outside the plasmapause. Whistlers provide important information on magnetospheric conditions during wave-particle interaction periods, for example, on equatorial electron densities and path magnetic shell parameters needed in modeling studies of observed interactions. 71 references