Preliminary ionospheric and airglow results of project ISAAC

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The research vessel S. A. AGULHAS undertook a voyage in the region of the South Atlantic Anomaly during June/July 1983. In the present paper a preliminary analysis of the ionospheric and airglow observations made from the ship is given. It was found that the ionization density in the F layer in the Anomaly is larger at its maximum near noon than that at a station at a comparable latitude outside the Anomaly, but that its minimum value at night is considerably smaller. Particle types of sporadic E ionization were encountered much more frequently at night in the Anomaly than outside, auroral, particle, flat and retardation types all being observed, the auroral type reaching a critical frequency for the ordinary ray of 7MHz on one occasion. 391.4nm airglow was observed to coincide with particle sporadic E traces on two occasions, but on one night this airglow emission was observed in the absence of sporadic E ionization. It is concluded that there is definite evidence that particles play a more important part in ionizing the E region in the Anomaly than at comparable latitudes elsewhere.