Lower thermosphere molecular oxygen derived from the volume emission rate of the Atmospheric band

In the lower thermosphere (above about 100 km altitude), the production of the upper state of the O2 Atmospheric band during the day is dominated by quenching of O(1D) by O2. O(1D) is primarily created by Schumann-Runge photolysis of O2 in the daytime lower thermosphere. The chemistry of this process is well understood and it is possible to use the volume emission rate of the O2 Atmospheric A band to recover the density of O2. Studying the A band emission is interesting because it has been measured continuously since late 1991, first by the HRDI instrument on UARS followed by the TIDI instrument on TIMED. These instruments measure the brightness of individual rotational lines in the Atmospheric A band which are inverted to recover the volume emission rate. The length of this record allows various components of the intra-annual variability to be examined. This paper will discuss the technique used to recover the O2 density and illustrate it by using recoveries from HRDI and TIDI data. Periodogram analysis will be used to infer the presence of various long-term components in the data.