Odin is a 250 kg class satellite built in co-operation between Sweden, Canada, France, and Finland and launched in February 2001. It carries two instruments: a 4-band sub-millimetre radiometer used for both astronomy and atmospheric science and an optical spectrometer and infrared imaging system for purely atmospheric observations. As part of the joint mission Odin will observe the atmospheric limb for 50% of the observation time producing profiles of many species of interest in the middle atmosphere with a vertical resolution of 1–2 km. These species include, among others, ozone, nitrogen dioxide, chlorine monoxide, nitric acid, water vapour, and nitrous oxide. An overview of the mission and the planned measurements is given. PACS Nos.: 42.68Mj, 94.10Dy, 95.55Fw

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 µm and the OH (3-1) Meinel band at 1.53 µm. 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.Résumé : Le système de spectrographie optique et d'imagerie infrarouge (OSIRIS) à bord du satellite Odin est conçu pour enregistrer les profils en altitude des éléments mineurs de l'atmosphère en observant les profils de radiance du limbe. Le spectrographe optique à réseau (OS) obtient les spectres de la lumière solaire diffusée sur le domaine entre 280-800 nm, avec une résolution spatiale approximative de 1 nm. Le satellite Odin balaye verticalement le limbe de façon répétée, de telle sorte que l'ouverture verticale de 1 km du OS parcoure les domaines voulus entre 10 et 100 km. Nous analysons les spectres solaires diffusés en superposition avec les caractéristiques terrestres d'absorption, afin de déterminer les profils en altitude des éléments mineurs de l'atmosphère. Le spectrographe détecte aussi la luminescence nocturne atmosphérique qui peut être utilisé pour étudier la mésosphère et la thermosphère. L'autre partie d'OSIRIS est un imageur infrarouge (IRI) à trois canaux qui utilise une banque linéaire de détecteurs pour imager la radiance du limbe sur un domaine d'altitude d'approximativement 100 km. L'IRI observe à la fois la lumière solaire diffusée et les émissions de luminescence nocturne atmospérique provenant de la bande infrarouge de l'oxygène atmosphérique à 1.27 µm et la bande de Meinel de l'OH (3-1) à 1.53 µm. Nous utilisons une technique d'inversion tomographique avec une série de ces images verticales pour obtenir la distribution bidimensionnelle des émissions à l'intérieur de l'orbite.[Traduit par la Rédaction] Can.

The ozone profile records of a large number of limb and occultation satellite instruments are widely used to address several key questions in ozone research. Further progress in some domains depends on a more detailed understanding of these data sets, especially of their long-term stability and their mutual consistency. To this end, we made a systematic assessment of 14 limb and occultation sounders that, together, provide more than three decades of global ozone profile measurements. In particular, we considered the latest operational Level-2 records by SAGE II, SAGE III, HALOE, UARS MLS, Aura MLS, POAM II, POAM III, OSIRIS, SMR, GOMOS, MIPAS, SCIAMACHY, ACE-FTS and MAESTRO. Central to our work is a consistent and robust analysis of the comparisons against the ground-based ozonesonde and stratospheric ozone lidar networks. It allowed us to investigate, from the troposphere up to the stratopause, the following main aspects of satellite data quality: long-term stability, overall bias and short-term variability , together with their dependence on geophysical parameters and profile representation. In addition, it permitted us to quantify the overall consistency between the ozone profilers. Generally, we found that between 20 and 40 km the satellite ozone measurement biases are smaller than ±5 %, the short-term variabilities are less than 5-12 % and the drifts are at most ±5 % decade −1 (or even ±3 % decade −1 for a few records). The agreement with ground-based data degrades somewhat towards the stratopause and especially towards the tropopause where natural variability and low ozone abundances impede a more precise analysis. In part of the stratosphere a few records deviate from the preceding general conclusions ; we identified biases of 10 % and more (POAM II and SCIAMACHY), markedly higher single-profile variability (SMR and SCIAMACHY) and significant long-term drifts (SCIAMACHY, OSIRIS, HALOE and possibly GO-MOS and SMR as well). Furthermore, we reflected on the repercussions of our findings for the construction, analysis and interpretation of merged data records. Most notably, the discrepancies between several recent ozone profile trend assessments can be mostly explained by instrumental drift. This clearly demonstrates the need for systematic comprehensive multi-instrument comparison analyses.

[1] We have studied the short-term effect of the October-November 2003 series of solar proton events on the middle atmosphere. Using the proton flux measurements from the GOES-11 satellite as input, we modeled the effect of the precipitating particles between 26 October and 6 November with a one-dimensional ion and neutral chemistry model. Then we compared the results with ground-based radio propagation measurements, as well as with NO 2 and ozone profiles made by the GOMOS satellite instrument. The very low frequency signal experiences up to À7 dB absorption during the largest solar proton event, subsequently varying with time of day during the recovery phase. The model and radio propagation observations show very good agreement, suggesting that the model is capturing the impact of solar protons on the ionosphere. The model results show order-of-magnitude changes in odd hydrogen and odd nitrogen concentrations, as well as ozone depletion varying from 20% at 40 km altitude to more than 95% at 78 km. The magnitude and altitude distribution of ozone depletion is found to depend not only on the flux and energy of the protons but also on the diurnal cycle of atomic oxygen and ozone-depleting constituents so that the largest depletions of ozone are seen during sunrise and sunset. The after-event recovery of ozone is altitude-dependent because of the differences in the recovery of odd hydrogen and odd nitrogen and also because of a relatively faster ozone production at higher altitudes. The modeled and measured NO 2 profiles agree well at altitudes 35-60 km, particularly during times of large concentrations observed after the solar proton event onset. A comparison of the time series of ozone depletion shows a good agreement between the model and observations.

Abstract.We have studied data from two satellite occultation instruments in order to generate a high vertical resolution homogeneous ozone time series of 26 yr. The Stratospheric Aerosol and Gas Experiment (SAGE) II solar occultation instrument and the Global Ozone Monitoring by Occultation of Stars (GOMOS) instrument measured ozone profiles in the stratosphere and mesosphere from 1984-2005 and 2002-2012, respectively. Global coverage, good vertical resolution, and the self-calibrating measurement method make data from these instruments valuable for the detection of changes in vertical distribution of ozone over time. As both instruments share a common measurement period from 2002-2005, it is possible to inter-calibrate the data sets. We investigate how well these measurements agree with each other and combine all the data to produce a new stratospheric ozone profile data set. Above 55 km, SAGE II measurements show much less ozone than the GOMOS nighttime measurements as a consequence of the well-known diurnal variation of ozone in the mesosphere. Between 35-55 km, SAGE II sunrise and sunset measurements differ from GOMOS' measurements to different extents. Sunrise measurements show 2 % less ozone than GOMOS, whereas sunset measurements show 4 % more ozone than GOMOS. Differences can be explained qualitatively by the diurnal variation of ozone in the stratosphere recently observed by SMILES and modeled by chemical transport models. Between 25-35 km, SAGE II sunrise and sunset measurements and GOMOS measurements agree within 1 %.The observed ozone bias between collocated measurements of SAGE II sunrise/sunset and GOMOS night measurements is used to align the two data sets. The combined data set covers the time period 1984-2011, latitudes 60 • S-60 • N, and the altitude range of 20-60 km. Profile data are given on a 1 km vertical grid, and with a resolution of 1 month in time and 10 • in latitude. The combined ozone data set is analyzed by fitting a time series model to the data. We assume a linear trend with an inflection point (so-called "hockey stick" form). The best estimate for the point of inflection was found to be the year 1997 for ozone between altitudes 35 and 45 km. At all latitudes and altitudes from 35 to 50 km we find a clear change in ozone trend before and after the inflection time. From 38 to 45 km, a negative trend of 4 % per decade (statistically significant at 95 % level) at the equator has changed to a small positive trend of 0-2 % per decade. At mid-latitudes, the negative trend of 4-8 % per decade has changed to to a small positive trend of 0-2 % per decade. At mid-latitudes near 20 km, the ozone loss has still increased whereas in the tropics a recovery is ongoing.