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Results are reported of ionospheric sounding and polarization rotation measurements made at a series of stations across West Africa during the total solar eclipse of 30 June 1973. A weak ionospheric disturbance identified by a minimum in both peak density and total electron content appears to be associated with the eclipse, propagating over a limited distance in the form of a bow wave. A small wave of period 18 min may also be eclipse produced, the wavelength being comparable to the size of the umbral region. Possible mechanisms for the generation of atmospheric waves and ionospheric disturbances by an eclipse are discussed but no firm conclusion has been reached concerning the source of the observed fluctuations.

A brief outline is given of the experimental technique used during the Cold Arctic Mesopause Project to record the first D -region ion line spectra with the EISCAT incoherent scatter radar. The data analysis shows that echoes from mesospheric heights between about 70 km and 90 km can be detected during disturbed periods of enhanced electron density during particle precipitation events. Electron density profiles were determined which show a fairly high density, up to 5 × 10 10 m −3 in the upper D -region. The measured meridional winds were lower than 10 m s −1 . A fit of the measured height profile of spectral width to temperature and neutral density models yielded a measured temperature profile in good agreement with simultaneous rocket data. The mesopause temperature was determined to be as low as 130 K. This detailed analysis of the spectral width profile indicates that below about 77–80 km the ratio of negative ions to electrons exceeded unity. Finally, some discussions are added on the limitations and significance of these first mesosphere observations.

Simultaneous observations of an ionospheric wave by two incoherent scatter facilities and three Faraday-rotation polarimeters have provided measurements of the frequency, vertical wavelength, horizontal wavelength and direction of propagation of the wave. These measured values confirm the Hines dispersion equation for atmospheric gravity waves.

Results are reported of a co-ordinated experimental study of medium scale gravity waves involving use of a multistatic incoherent scatter system together with two networks of polarimeters monitoring transmissions from a geostationary satellite during a six-day period in July 1974. The latter observations give access to the horizontal propagation parameters of the waves while the former technique yields information on the vertical structure of both waves and the ambient atmosphere. A reverse ray tracing analysis, through the atmosphere, for each gravity wave is described and its validity and accuracy discussed in detail. For the majority of the waves the reverse group path can be followed down to tropopause level and comparison with meteorological data has shown that many of the possible source regions of the observed waves appear to lie in proximity to the jet stream, with some evidence to suggest a preference for the polar side of the jet. Other wave sources are found to be close to regions of convectively unstable cold polar air. Wave energetics are discussed together with possible generation mechanisms, the latter in the form of non-linear interaction of shear flow instabilities in the jet stream and penetrative convection.