Ian C. McDade

ETON 2: Quenching parameters for the proposed precursors of O2(b1Σg+) and O(1S) in the terrestrial nightglow

Abstract Volume emission profiles of the O 2 ( b 1 Σ g + − X 3 Σ g t - )( O - O ) Atmospheric Band and the O( 1 S- 1 D) green line are used together with coordinated measurements of the atomic oxygen concentrations to test the hypothesis that both emissions are excited by Barth type mechanisms. By considering O 2 ( b 1 Σ g + ) to be produced from an excited O 2 precursor, with O 2 as transfer agent, and O( 1 S) to be formed from a similar precursor with atomic oxygen as the transfer agent, precursor quenching rates are obtained as a function of altitude. These quenching profiles can be well resolved into components corresponding to collisional deactivation by O( 3 P) and O 2 (or N 2 ), and support the suggestion that Barth type mechanisms are involved. Minimum efficiencies for the production of the two precursors in oxygen atom recombination and ratios for the quenching of each by O( 3 P) and O 2 (or N 2 ) are deduced. Differences in the quenching coefficients for the two precursors are discussed.

ETON 1: A data base pertinent to the study of energy transfer in the oxygen nightglow

Abstract A comprehensive group of experiments, assembled and flown on a series of Petrel rockets in March 1982 for the primary purpose of investigating the extent to which energy transfer is important in the excitation of the oxygen nightglow, is briefly described. Aspects of the data reduction methods are summarised and the bulk of the processed data is presented in profile and tabular form as a base for modelling and analyses in papers to follow and in evidence of the quality and success of this memorable international collaborative campaign.

An assessment of proposed O(1S) and O2(b1Σg+) nightglow excitation parameters

Abstract A database consisting of a number of simultaneously measured O( 1 D- 1 S) green line and O 2 ( b 1 Σ g + ) − X 3 Σ g )(0,0) atmospheric band nightglow emission profiles is examined to assess the general validity of the airglow excitation parameters recently proposed by McDade et al . (1986, Planet. Space Sci ., 34 , 789). The measured profiles were obtained under quite diverse atmospheric conditions and should, therefore, allow a critical assessment of the proposed parameters. Model green line emission profiles, calculated from the measured O 2 atmospheric band emission profiles using the proposed parameters, are compared with the green line profiles actually measured on each occasion. The measured and modelled green line profiles are found to be in good agreement under most conditions. The cases for which discrepancies exist are discussed in terms of inadequacies in either the background atmosphere adopted for the analyses or in the parameters themselves.

Polar vortex evolution during the 2002 Antarctic major warming as observed by the Odin satellite

In September 2002 the Antarctic polar vortex split in two under the influence of a sudden warming. During this event, the Odin satellite was able to measure both ozone (O3) and chlorine monoxide (ClO), a key constituent responsible for the so-called “ozone hole”, together with nitrous oxide (N2O), a dynamical tracer, and nitric acid (HNO3) and nitrogen dioxide (NO2), tracers of denitrification. The submillimeter radiometer (SMR) microwave instrument and the Optical Spectrograph and Infrared Imager System (OSIRIS) UV-visible light spectrometer (VIS) and IR instrument on board Odin have sounded the polar vortex during three different periods: before (19–20 September), during (24–25 September), and after (1–2 and 4–5 October) the vortex split. Odin observations coupled with the Reactive Processes Ruling the Ozone Budget in the Stratosphere (REPROBUS) chemical transport model at and above 500 K isentropic surfaces (heights above 18 km) reveal that on 19–20 September the Antarctic vortex was dynamically stable and chemically nominal: denitrified, with a nearly complete chlorine activation, and a 70% O3 loss at 500 K. On 25–26 September the unusual morphology of the vortex is monitored by the N2O observations. The measured ClO decay is consistent with other observations performed in 2002 and in the past. The vortex split episode is followed by a nearly complete deactivation of the ClO radicals on 1–2 October, leading to the end of the chemical O3 loss, while HNO3 and NO2 fields start increasing. This acceleration of the chlorine deactivation results from the warming of the Antarctic vortex in 2002, putting an early end to the polar stratospheric cloud season. The model simulation suggests that the vortex elongation toward regions of strong solar irradiance also favored the rapid reformation of ClONO2. The observed dynamical and chemical evolution of the 2002 polar vortex is qualitatively well reproduced by REPROBUS. Quantitative differences are mainly attributable to the too weak amounts of HNO3 in the model, which do not produce enough NO2 in presence of sunlight to deactivate chlorine as fast as observed by Odin.

Eton 5: Simultaneous rocket measurements of the OH meinel Δυ = 2 sequence and (8,3) band emission profiles in the nightglow

Abstract Simultaneous rocket measurements of the emission profiles of the OH Meinel (8,3) band and the Δυ = 2 sequence at 1.61 μm are presented and analysed. It is shown that the υ = 8 level of the hydroxyl radical must suffer significant loss in the mesosphere due to collisions with O2 and/or N2. The rate coefficients for this removal process are obtained, for certain limiting assumptions about the excitation mechanism, and the coefficients are found to be in good agreement with those deduced from an independent analysis of ground-based observations. A variety of kinetic models, which reproduce the observed (8,3) band profile in some detail, predict Δυ = 2 sequence emission profiles which compare favourably with the measured profile in their total zenith intensities but not in their altitude distributions. The differences between the measured and modelled Δυ = 2 altitude profiles suggest that the 1.61 μm observations may have been contaminated by some unidentified vehicle-induced emission.

The Wind Imaging Interferometer (WINDII) on the Upper Atmosphere Research Satellite: A 20 year perspective

The Wind Imaging Interferometer (WINDII) was launched on the NASAs Upper Atmosphere Research Satellite on 12 September 1991 and operated until 2003. Its role in the mission was to measure vector winds in the Earths atmosphere from 80 to 110 km, but its measurements extended to nearly 300 km. The approach employed was to measure Doppler shifts from a suite of visible region airglow lines emitted over this altitude range. These included atomic oxygen O(1S) and O(1D) lines, as well as lines in the OH Meinel (8,3) and O2 Atmospheric (0,0) bands. The instrument employed was a Doppler Michelson Interferometer (DMI) that measured the Doppler shift as a phase shift of the cosinusoidal interferogram generated by single airglow lines. An extensive validation program was conducted after launch to confirm the accuracy of the measurements. The dominant wind field, the first one observed by WINDII, was that of the migrating diurnal tide at the equator. The overall most notable WINDII contribution followed from this; determining the influence of dynamics on the transport of atmospheric species. Currently, non-migrating tides are being studied in the thermosphere at both equatorial and high latitudes. Other aspects investigated included solar and geomagnetic influences, temperatures from atmospheric scale heights, nitric oxide concentrations and the occurrence of polar mesospheric clouds. The results of these observations are reviewed from a perspective of twenty years. A future perspective is then projected, involving more recently developed concepts. It is intended that this description will be helpful for those planning future missions.

Retrieval of stratospheric O3 and NO2 profiles from Odin Optical Spectrograph and Infrared Imager System (OSIRIS) limb-scattered sunlight measurements

Scientific studies of the major environmental questions of global warming and ozone depletion require global data sets of atmospheric constituents with relevant temporal and spatial resolution. In this paper global number density profiles of O3 and NO2 are retrieved from Odin/OSIRIS limb-scattered sunlight measurements, using the Maximum A Posteriori estimator. Differential Optical Absorption Spectroscopy is applied to OSIRIS radiances as an intermediate step, using the wavelength windows 571-617 nm for O3 and 435-451 nm for NO2. The method is computationally efficient for processing OSIRIS data on an operational basis. Results show that a 2-3 km height resolution is generally achievable between about 12 km and 45 km for O3 with an estimated accuracy of 13\% at the peak and between about 15 km and 40 km for NO2 with an estimated accuracy of 10\% at the peak. First validations of the retrieved data indicate a good agreement both with other retrieval techniques applied to OSIRIS measurements and with the results of other instruments. Once the validation has reached a confident level, the retrieved data will be used to study important stratospheric processes relevant to global environmental problems. The unique NO2 data set will be of particular interest for studies of nitrogen chemistry in the middle atmosphere.

Stratospheric profiles of nitrogen dioxide observed by Optical Spectrograph and Infrared Imager System on the Odin satellite

[1] Vertical profiles of nitrogen dioxide in the 19–40 km altitude range are successfully retrieved over the globe from Optical Spectrograph and Infrared Imager System (OSIRIS) limb scatter observations in late 2001 and early 2002. The inclusion of multiple scattering in the radiative transfer model used in the inversion algorithm allows for the retrieval of NO2 down to 19 km. The slant column densities, which represent the observations in the inversion, are obtained by fitting the fine structure in normalized radiance spectra over the 435–449 nm range, where NO2 electronic absorption is readily observable because of long light paths through stratospheric layers rich in this constituent. Details of the spectral fitting and inversion algorithm are discussed, including the discovery of a pseudo-absorber associated with pixelated detectors and a new method to verify altitude registration. Comparisons are made with spatially and temporally coincident profile measurements of this photochemically active trace gas. Better than 20% agreement is obtained with all correlative measurements over the common retrieval altitude range, confirming the validity of OSIRIS NO2 profiles. Systematic biases in the number densities are not observed at any altitude. A ‘‘snapshot’’ meridional cross section between 40� N and 70� S is shown from observations during a fraction of an orbit. INDEX TERMS: 0340 Atmospheric Composition and Structure: Middle atmosphere—composition and chemistry; 0360 Atmospheric Composition and Structure: Transmission and scattering of radiation; 0394 Atmospheric Composition and Structure: Instruments and techniques; 3334 Meteorology and Atmospheric Dynamics: Middle atmosphere dynamics (0341, 0342); KEYWORDS: optical, Sun-synchronous, polar-orbiting, Fraunhofer, Ring effect, iterative onion peel

The altitude dependence of the OH(X2Π) vibrational distribution in the nightglow : some model expectations

Abstract A number of different OH Meinel band excitation models are used to investigate the extent to which quenching and vibrational deactivation processes could cause the nightglow OH vibrational distributions to vary with altitude. The various models, which are based upon those described by McDade and Llewellyn (1988, Planet. Space Sci.36, 897), are used to calculate the steady state OH vibrational distributions throughout the 80–100 km region. The results of the calculation show that, irrespective of the basic model assumptions, the OH vibrational distributions should not be strongly altitude dependent and that the emission profiles of the Meinel bands from the υ′ levels 1 through 9 should not differ in altitude by more than one or two kilometers. The results of some recent laboratory studies pertaining to the Meinel band excitation mechanism are also discussed and it is shown that stepwise collisional vibrational deactivation is unlikely to play a major role in controlling the observed nightglow OH vibrational distribution.

ETON 3: Altitude profiles of the nightglow continuum at green and near infrared wavelengths

Abstract Rocket-borne photometer measurements of the nightglow continuum at 5400 A and 7140 A are reported for conditions close to equinox at mid-latitude. The 5400 A emission rates are used to determine nitric oxide concentrations under the assumption that the emission at this wavelength arises entirely from the chemiluminescent recombination of nitric oxide and atomic oxygen. The derived nitric oxide concentrations, although in keeping with those previously determined using this technique, are slightly larger than those predicted by current model calculations. The concentrations derived from the 7140 A emission rates, under the same assumption, are significantly larger between 90 and 100 km than those obtained from the 5400 A data. It is concluded that another source of nightglow radiation must exist in the 7140 A region. The altitude profile of the additional near i.r. emission is determined and its possible origins are discussed.