Airglow and the South Atlantic Geomagnetic Anomaly

Abstract

Dessler [1959] suggested why the Capetown anomaly of the geomagnetic field should explain the ‘slot’ between the inner and outer zones of trapped radiation. For present considerations this anomaly is regarded as a part of the large negative anomaly (here called the South Atlantic anomaly) which extends from the South China Sea southeast across Brazil and into the Indian Ocean off South Africa. One would expect a region of luminosity in the earth's upper atmosphere to be related to this feature of the geomagnetic field. Now the observations of the spectral line 5577 A in the airglow reported by Nakamura [1958] show high intensities in the range 15°–40° (geographic latitude). It is suggested here that these large values in the 5577 A emission are partly due to the South Atlantic anomaly. It seems more than coincidence that the peaks of Nakamura's observations were obtained as the recording ship Soya passed through the South China Sea end and the South African end of this anomaly. Recent work [Huruhata and Nakamura, 1960] suggests a seasonal effect as well. This may be the result of seasonal variation in atmospheric density at mirror point heights.