Some peculiarities of altitudinal distribution of atomic oxygen at low latitudes during magnetic storms

Several storms were examined during the period of the ESRO-4 mission to study the altitudinal behaviour of atomic oxygen and molecular nitrogen at low latitudes. A special method of data reduction was applied to distinguish composition changes due to thermal expansion and those which resulted from some non-thermal process. It was shown that in the majority of cases studied there exists some latitudinal interval where changes of the N 2/O ratio from quiet to storm days are small compared with that observed in the purely thermal case. This latitudinal interval was found to be displaced to the winter hemisphere (not always across the equator) during solstice cases and the corresponding altitudinal interval was sometimes equal to the whole height range covered by the satellite. The effective temperature of atomic oxygen turned out to be greater than that deduced from the altitudinal distribution of N 2. This implies that there exists a non-thermal component of the [O] increase on a storm day at low latitudes and thus [O] is distributed in a non-barometric way. A possible mechanism responsible for this behaviour is downwelling due to the disturbed global thermospheric circulation.