JOURNAL OF GEOPHYSICAL RESEARCH, VOL. 100, NO. A9, PAGES 17,415-17,428, SEPTEMBER 1, 1995 Inference of atomic oxygen concentration from remote sensing of optical aurora M. G. Shepherd, 1'2 J. C. McConnell, 3 W. K. Tobiska, 4 G. R. Gladstone, s S.Chakrabarti, 6 and G. Schmidtke * Abstract. A remote sensing method has been developed for the determination of the [OI/[O-MSIS] ratio in aurora, using ra, tios of theO I (557.7 nm)and N2 + (391.4 nm) emissions. It is shown that the method ca, n be used for the analysis of measurements integrated along the line of sight,provided data only above the emission rate peak are used. The method is applied to the caseof horizontal viewing from a vertically oriented rocket so that a large volumeof space was saxnpled aroundthe rocket. The methodcan potentiallybe appliedto satellitelimb images, provided some independent information about the location of the aurorais available,a.s it was for the rocket observations. Photometricmeasurements of the N2 + (391.4 nm)and O I (557.7 nm)emissions obtained during theEnergy Budget Campaign 1980 on flight E-2 with the instrumentEFll and its reflight in 1981 were used in the analysis presented. During the first flight the rockethorizontally viewed two distinct aurorae, a nearby diffusepatch, and a more distant pulsating aurora. Resultsobtained by the sameEFll instrumenton a second flight through an auroral arc in 1981 are alsopresented.Two types of atomic oxygen variability were found in bothof the flights. In the first type, [O]is increased above [O-MSIS] by a factorof 1.5 at 180kin, is equalto the MSIS model at 160kin, and is less than MSIS below that; that is, the scale heightof [O] wasincreased. The experimental I(557.7)/I(391.4) ratiowas constant with altitude.In the second type,the [O] was depleted by about a factor of 2 over the altitude rangeof 120-180 km, while the 1(557.7)/I(391.4)ratio decreased with altitude. The inferred atomicoxygen concentrations of 0.5 to 2 with respect to MSIS suggested different vertical flows on the two cases. Independentevidence is providedby atmospheric composition measurements made during the same campaign. Introduction The traditional technique for rocketinvestigation of aurora[e.g. Sharpel al., 1979a, b; Vallance Jones el al., 1991] employs vertically viewing photometers that ideally view up the magnetic field line, while the source electron energy spectrum is measured on the same field line abovethe aurora. The energydeposition by this electron spectrum is computed from a model,and the 1Herzberg Institute of Astrophysics, NRCC, Ottawa, Ontario, Canada. 2Now at Centre for Research in Earth and Space Sciences, York University, Toronto, Ontario, Canada. 3Centre for Research in Earth and SpaceSciences, York Uni- versity, Toronto, Ontario, Canada. 4 TELOS/Jet Propulsion Laboratory, Pasadena, California. sSouthwest Research Institute, San Antonio, Texas. 6Center for Space Physics,Boston University, Boston, Mas- sachusetts. ? Institut fiir Physikahsche Messtechnik, Freiburg, Germany. Copyright 1995 by the American Geophysical Union. Paper number 94JA03374. 0148-0227/95/94JA-03374505.00 resultingoptical emissions are calculated and compared with observations. This method addresses the whole auroral problem involvingenergydeposition, excitation mechanisms, and atmospheric composition, but the en- tire data set is based on the determination of a single vertical profile associated with oneelectronenergyspec- trum. This is a good way to study detailedphotochem- ical processes, but for the study of atmospheric com- position in aurora one wishes to samplea larger region of the atmosphere. This can only be done by remote sensing, and tomographic methods havebeenemployed by Solomon et al. [1988] for the Visible AirglowEx- periment instrument on the AE-C satellite [Hayset al., 1973b]and by McDade et al. [1991]. In both cases a photometer viewedperpendicular to the spin axis, which itself was perpendicular to the vehicle velocity vector. Emission rates integratedalongthe line of sight were inverted to volume emission rate profiles alongthe satellite track. In this paper we explore two new aspectsof auro- ral remote sensing. First, we show how the auroral emission rate ratio O(•S)557.7 nm/N•+391.4 nmcan be usedto infer the atomic oxygenconcentration in an au- rora. Second, we show that this method canbe used for 17,415