A new method of deducing the atomic oxygen density profiles in the lower thermosphere using ground-based night airglow observations

Abstract

A semi-empirical method has been developed to deduce the atomic oxygen density profile in the altitude range of 90 to 120 km at any instant at night, making use of the ground-based night airglow observations of (OI) 5577Å, (OI) 6300Å and OH band emission zenith intensities. Following Reed and Chandra (1975) the shape of the atomic oxygen profile is assumed to be of the Chapman type, of the form: [ O] z = [ O] m exp 1 2 [1− Z−Z m S · H ] The scale height ( H) is determined from the rotational temperature obtained from observed OH emissions. The value of the mixing factor ( S) is assumed from theory. An empirical linear relationship between the modified scale height SH and Z m , the height of maximum of density has been established, using which Z m is determined. E-region component of 5577Å line intensity is obtained from the observed total 5577Å intensity by subtracting the F-region component determined by using the 6300Å line intensity. From this, [ O] m , the maximum of [O] density, is determined using the expression of Reed and Chandra (1975). Thus knowing all the unknowns in the above expression, the [O] profile is deduced. From the night airglow observations made at Kodaikanal during the spring equinox of 1978, the mean [O] profiles between 90 and 120 km for each hour of the night have been computed using the above method.