E. J. Llewellyn

Atmospheric Chemistry Experiment (ACE): Mission overview

SCISAT-1, also known as the Atmospheric Chemistry Experiment (ACE), is a Canadian satellite mission for remote sensing of the Earths atmosphere. It was launched into low Earth circular orbit (altitude 650 km, inclination 74°) on 12 Aug. 2003. The primary ACE instrument is a high spectral resolution (0.02 cm-1) Fourier Transform Spectrometer (FTS) operating from 2.2 to 13.3 μm (750-4400 cm-1). The satellite also features a dual spectrophotometer known as MAESTRO with wavelength coverage of 285-1030 nm and spectral resolution of 1-2 nm. A pair of filtered CMOS detector arrays records images of the Sun at 0.525 and 1.02 μm. Working primarily in solar occultation, the satellite provides altitude profile information (typically 10-100 km) for temperature, pressure, and the volume mixing ratios for several dozen molecules of atmospheric interest, as well as atmospheric extinction profiles over the latitudes 85°N to 85°S. This paper presents a mission overview and some of the first scientific results. Copyright 2005 by the American Geophysical Union.

The OSIRIS Instrument on the Odin Spacecraft

The optical spectrograph and infrared imager system (OSIRIS) on board the Odin spacecraft is designed to retrieve altitude profiles of terrestrial atmospheric minor species by observing limb-radiance profiles. The grating optical spectrograph (OS) obtains spectra of scattered sunlight over the range 280-800 nm with a spectral resolution of approximately 1 nm. The Odin spacecraft performs a repetitive vertical limb scan to sweep the OS 1 km vertical field of view over selected altitude ranges from approximately 10 to 100 km. The terrestrial absorption features that are superimposed on the scattered solar spectrum are monitored to derive the minor species altitude profiles. The spectrograph also detects the airglow, which can be used to study the mesosphere and lower thermosphere. The other part of OSIRIS is a three-channel infrared imager (IRI) that uses linear array detectors to image the vertical limb radiance over an altitude range of approximately 100 km. The IRI observes both scattered sunlight and the airglow emissions from the oxygen infrared atmospheric band at 1.27 mum and the OH (3-1) Meinel band at 1.53 mum. A tomographic inversion technique is used with a series of these vertical images to derive the two-dimensional distribution of the emissions within the orbit plane.

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.

A measurement of the O2(b1Σg+−X3Σg−) atmospheric band and the OI(1S) green line in the nightglow

Abstract Simultaneous measurements of the nightglow profiles of the O2(b1Σg+−X3Σg−) A-band, the atomic oxygen green line and the OH (8−3) Meinel band are presented. The altitude profiles are used to determine both the excitation mechanisms for the oxygen emissions and the atomic oxygen altitude distribution. It is shown that the measurements are consistent with a green line excitation through the Barth mechanism and that the molecular oxygen emission is excited through oxygen recombination and the reaction between OH∗ and atomic oxygen. The derived atomic oxygen concentrations,6.2 × 1011cm−3at 98km, are consistent with the Jacchia (1971) model.

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.

The quenching of OH∗ in the atmosphere

Abstract The intensity distribution of the OH Meinel bands in the airglow has been derived from the minor constituent profiles of Moreels et al. (1977). It has been shown that there is good agreement between the observed and calculated intensity distribution for excitation through the hydrogen-ozone reaction and quenching of the excited state by reaction with atomic oxygen and through vibrational relaxation. The rate constants for vibrational relaxation have been derived and are found to be vibrational level dependent; for the ν = 7 level, the peak value, the rate constant is 5.8 × 10−12cm3s−1.

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.

Longitudinal structure in atomic oxygen concentrations observed with WINDII on UARS

WINDII, the Wind Imaging Interferometer on the Upper Atmosphere Research Satellite, began atmospheric observations on September 28, 1991 and since then has been collecting data on winds, temperatures and emissions rates from atomic, molecular and ionized oxygen species, as well as hydroxyl. The validation of winds and temperatures is not yet complete, and scientific interpretation has barely begun, but the dominant characteristic of these data so far is the remarkable structure in the emission rate from the excited species produced by the recombination of atomic oxygen. The latitudinal and temporal variability has been noted before by many others. In this preliminary report on WINDII results we draw attention to the dramatic longitudinal variations of planetary wave character in atomic oxygen concentration, as reflected in the OI 557.7 nm emission, and to similar variations seen in the Meinel hydroxyl band emission.