Global O/N-2 derived from DE 1 FUV dayglow data: Technique and examples from two storm periods

A technique is presented for deriving the column abundance of O relative to N-2 (designated as O/N-2 and referenced to an N-2 depth of 10(17) cm(-2)) from DE 1 imager dayglow data. For the band-pass filter of interest, the da ta are dominated by O I 130.4, nm with minor contributions from O I 135.6 n m and N-2 Lyman-Birge-Hopfield. The technique relies on a first-principles calculation of the intensity I-1P for the given band pass. Independent vari ables are solar zenith angle S, look angle D, and O/N-2. There is a degree of nonuniqueness between I-1P and O/N-2 (similar to 10%), which is accounte d for in our error analysis. A bias exists between I-1P and a given data se t owing to errors in cross sections, the assumed solar EUV flux, and calibr ation. The bias is removed by scaling I-1P to agree with quiet time data as close in time as possible with the data set of interest. A comparison of t he behavior of I-1P versus S and D is made with the empirical model of Crav en and colleagues [Craven ct al., 1994; Nicholas cf al., 1997; Immel et al. , 1997], which shows satisfactory agreement for S > 40 degrees but some sig nificant departures at smaller angles. Sequences of O/N-2 images over 2-day periods are presented for geomagnetic storms commencing on days 267 and 29 5, 1981. Both storms produced major O depleted patches at midlatitudes to h igh latitudes, with extreme values of O/N-2 more than a factor of 2 smaller than undisturbed values. The results also show longitudinal motions of the patches over the reporting periods.