| 1. |
- Barret, B., et al.
(författare)
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Intercomparisons of trace gases profiles from the Odin/SMR and Aura/MLS limb sounders
- 2006
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Ingår i: Journal of Geophysical Research. - 0148-0227 .- 2156-2202. ; 111:D21
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Tidskriftsartikel (refereegranskat)abstract
- This paper presents the intercomparison of O(3), HNO(3), ClO, N(2)O and CO profiles measured by the two spaceborne microwave instruments MLS ( Microwave Limb Sounder) and SMR ( Submillimetre Radiometer) on board the Aura and Odin satellites, respectively. We compared version 1.5 level 2 data from MLS with level 2 data produced by the French data processor version 222 and 225 and by the Swedish data processor version 2.0 for several days in September 2004 and in March 2005. For the five gases studied, an overall good agreement is found between both instruments. Most of the observed discrepancies between SMR and MLS are consistent with results from other intercomparison studies involving MLS or SMR. O(3) profiles retrieved from the SMR 501.8 GHz band are noisier than MLS profiles but mean biases between both instruments do not exceed 10%. SMR HNO(3) profiles are biased low relative to MLS's by similar to 30% above the profile peak. In the lower stratosphere, MLS ClO profiles are biased low by up to 0.3 ppbv relative to coincident SMR profiles, except in the Southern Hemisphere polar vortex in the presence of chlorine activation. N(2)O profiles from both instruments are in very good agreement with mean biases not exceeding 15%. Finally, the intercomparison between SMR and MLS CO profiles has shown a good agreement from the middle stratosphere to the middle mesosphere in spite of strong oscillations in the MLS profiles. In the upper mesosphere, MLS CO concentrations are biased high relative to SMR while negative values in the MLS retrievals are responsible for a negative bias in the tropics around 30 hPa.
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| 2. |
- El Amraoui, L., et al.
(författare)
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Assimilation of Odin/SMR and O3 and N2O Measurements in a Three-dimensional Chemistry Transport Model
- 2004
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Ingår i: Journal of Geophysical Research. - 0148-0227 .- 2156-2202. ; 109:D22, s. 1-9
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Tidskriftsartikel (refereegranskat)abstract
- A method for assimilating observations of long-lived species such as ozone (O-3) and nitrous oxide (N2O) in a three-dimensional chemistry transport model (3D-CTM) is described. The model is forced by the temperature and wind analyses from the European Centre for Medium-Range Weather Forecasts (ECMWF). The O-3 and N2O fields used in this study are obtained from the Sub-Millimeter Radiometer (SMR) aboard the Odin satellite. The assimilation technique used is the sequential statistical interpolation approach. The parametrization of the error covariance matrix of the model forecast field is described. A sensitivity study of the system parameters is done in terms of the OMF (observation minus forecast) vector also called "innovation'' vector and in terms of the chi(2) (chi-square) test. The effect of the correlation distances is critical for the assimilated field. The RMS ( root mean square) of the OMF for the correlation distances is minimal for values of 1500 km in the meridional direction and 500 km in the zonal direction for both O-3 and N2O. The treatment of the meridional distance as a function of latitude does not reveal an important improvement. The chi(2) diagnostic shows that the asymptotic value of the model error ( the model error of saturation) is optimal for the value of 12.5% for O-3 and 18% for N2O. We demonstrate the applicability of the developed assimilation method for the Odin/SMR data. We also present first results of the assimilation of Odin/SMR ozone and nitrous oxide for the period from 22 December 2001 to 17 January 2002.
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| 3. |
- Jones, N., et al.
(författare)
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Stratomesospheric CO measured by a ground-based Fourier Transform Spectrometer over Poker Flat, Alaska: Comparisons with Odin/SMR and a 2-D model
- 2007
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Ingår i: Journal of Geophysical Research. - 0148-0227 .- 2156-2202. ; 112:D20
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Tidskriftsartikel (refereegranskat)abstract
- The interseasonal variability of stratomesospheric CO is reported from Poker Flat, Alaska, using spectra from a ground-based Fourier Transform Spectrometer (gb-FTS) for the time period from 2000 to 2004. The CO spectra were analyzed using an optimal estimation technique that separates the tropospheric and stratospheric/mesospheric components into partial columns. The distribution of CO in the polar winter is such that the gb-FTS retrieved partial column is weighted to the mesosphere. The gb-FTS data are compared with measurements of partial column CO from the Sub-Millimeter Radiometer on board the Odin satellite and shown to be in very good agreement despite the relatively small sample size. The mean difference of the two data sets indicates a small positive bias (7.6 +/- 6%) in favor of the Odin data, with a correlation coefficient, r(2) = 0.91. The gb-FTS data indicate that there is a strong seasonal dependence of the CO partial column that is consistent with known winter polar thermospheric descent of CO enriched air. Year-to-year variability is explained in terms of mesospheric wind dynamics, which show 2004 and components of 2002 were affected by earlier than expected breakdown (30 +/- 13 d) of the winter polar circulation compared with 2000 to 2003. Finally, the measured CO data is compared with a 2-D chemical transport model that gives support to the idea that springtime polar mesospheric CO is driven by meridional winds.
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| 4. |
- Urban, Joachim, 1964, et al.
(författare)
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Odin/SMR Limb Observations of Stratospheric Trace Gases: Level 2 Processing of ClO, N2O, O3, and HNO3
- 2005
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Ingår i: Journal of Geophysical Research. - 0148-0227 .- 2156-2202. ; 110:D14, s. 1-20
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Tidskriftsartikel (refereegranskat)abstract
- The Sub-Millimetre Radiometer (SMR) on board the Odin satellite, launched on 20 February 2001, observes key species with respect to stratospheric chemistry and dynamics such as O-3, ClO, N2O, and HNO3 using two bands centered at 501.8 and 544.6 GHz. We present the adopted methodology for level 2 processing and the achieved in-orbit measurement capabilities of the SMR radiometer for these species in terms of altitude range, altitude resolution, and measurement precision. The characteristics of the relevant level 2 data versions, namely version 1.2 of the operational processor as well as versions 222 and 223 of the reference code, are discussed and differences are evaluated. An analysis of systematic retrieval errors, resulting from spectroscopic and instrumental uncertainties, is also presented.
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| 5. |
- Urban, Joachim, 1964, et al.
(författare)
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Odin/SMR limb observations of stratospheric trace gases: Validation of N2O
- 2005
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Ingår i: Journal of Geophysical Research. - 0148-0227 .- 2156-2202. ; 110:9, s. D09301-20
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Tidskriftsartikel (refereegranskat)abstract
- The Sub-Millimetre Radiometer (Odin/SMR) on board the Odin satellite, launched on 20 February 2001, performs regular measurements of the global distribution of stratospheric nitrous oxide (N2O) using spectral observations of the J = 20→ 19 rotational transition centered at 502.296 GHz. We present a quality assessment for the retrieved N2O profiles (level 2 product) by comparison with independent balloonborne and aircraftborne validation measurements as well as by cross-comparing with preliminary results from other satellite instruments. An agreement with the airborne validation experiments within 28 ppbv in terms of the root mean square (RMS) deviation is found for all SMR data versions (v222, v223, and v1.2) under investigation. More precisely, the agreement is within 19 ppbv for N2O volume mixing ratios (VMR) lower than 200 ppbv and within 10% for mixing ratios larger than 150 ppbv. Given the uncertainties due to atmospheric variability inherent to such comparisons, these values should be interpreted as upper limits for the systematic error of the Odin/SMR N2O measurements. Odin/SMR N2O mixing ratios are systematically slightly higher than nonvalidated data obtained from the Improved Limb Atmospheric Spectrometer-II (ILAS-II) on board the Advanced Earth Observing Satellite-II (ADEOS-II). Root mean square deviations are generally within 23 ppbv (or 20% for VMR-N2O > 100 ppbv) for versions 222 and 223. The comparison with data obtained from the Michelson Interferometer for Passive Atmospheric Sounding (MIPAS) on the Envisat satellite yields a good agreement within 9-17 ppbv (or 10% for VMR-N2O > 100 ppbv) for the same data versions. Odin/SMR version 1.2 data show somewhat larger RMS deviations and a higher positive bias.
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