[en] The principal features that might exist in the terrestrial paleoionosphere, if the geomagnetic field were to assume a quadrupole form during a polarity reversal are discussed. Complicated phenomena would be expected to occur at magnetic equators and magnetospherically-driven plasma convection might occur at latitudes where the magnetic field is steeply inclined. The influence of magnetic field strength on ionospheric structure is considered in general terms

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[en] Ionospheric data from several stations are used to verify that, at any given local time, the mid-latitude F2 peak tends to lie at fixed values of atmospheric pressure, as expected from theory. The pressure values are found empirically to be about 2 x 10 to the -10th atmosphere at noon and 2 x 10 to the -11th atmosphere at midnight. Given that the global Mass Spectrometer/Incoherent Scatter (MSIS) model of the neutral thermosphere is now readily available, it is suggested that the constant pressure approach provides a simple way of modeling the height hmF2 for practical purposes, for a wide range of solar and geomagnetic activity, with better consistency than is given by methods based on ionosonde data alone. 16 refs

[en] The Eiscat system, of which the UHF component is due to enter service in 1979 and the VHF component in 1980, is briefly described. The paper discusses the expected performance of the system and some considerations and constraints involved in its use. (author)

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[en] The structure and dynamics of the thermosphere are reviewed in a general way, in relation to the properties of the ionospheric F region. Following a resume of F region theory, the paper discusses qualitatively the energy input to the thermosphere and F region. Some suggested thermospheric models and the wind patterns associated with them are then described. Such F region phenomena as seasonal, storm and semi-annual variations are also discussed. Some possible applications of EISCAT to studies of these phenomena are mentioned. (Auth.)

[en] Theoretical line-of-sight velocities, as would be observed by the EISCAT radar, are computed for idealized models of plasma convection in the polar ionosphere. The calculations give the velocity as a function of range and Universal Time. For several variants of the Volland and Heelis convection models, how the maxima, minima and reversals of velocity depend on beam azimuth is examined. The analysis is designed to be applied to data from the UK-POLAR experiment, an example of which is shown

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[en] The physical explanation of the changes of the maximum electron concentration of the F2 layer, NmF2, as a result of geomagnetic disturbances has proved elusive even after several decades of study. In this paper, we concentrate upon the main phase of the F-region storm which usually begins a few hours after the onset of a significant increase of geomagnetic activity. We present some new analysis of ionosonde data from the South Atlantic and Antarctica. There are major differences in storm phenology in the South compared with the North. In winter in the South, NmF2 is usually increased as the result of a geomagnetic storm whereas in the North it is depressed. In summer, both hemispheres normally show reduced values of NmF2 as a result of storm activity. It is these features which provide new insight into the problem of F-region storms. We interpret the observed seasonal and diurnal variation of NmF2 in terms of a mean (DC) effect and a diurnal variation (AC) effect, and discuss possible explanations for both. (author)