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Chauhan S,
Höpfner M,
G. P. Stiller,
T. von Clarmann,
Funke B,
Glatthor N,
Grabowski U,
Linden A,
Kellmann S,
Milz M, Steck T,
Fischer H,
Froidevaux L,
Lambert A,
M. L. Santee,
Schwartz M,
W. G. Read,
N. J. Livesey
[show abstract]
[hide abstract]
ABSTRACT: During several periods since 2005 the Michelson Interferometer for Passive Atmospheric Sounding (MIPAS) on Envisat has performed observations dedicated to the region of the upper troposphere/lower stratosphere (UTLS). For the duration of November/December 2005 global distributions of temperature and several trace gases from MIPAS UTLS-1 mode measurements have been retrieved using the IMK/IAA (Institut für Meteorologie und Klimaforschung/Instituto de Astrofísica de Andalucía) scientific processor. In the UTLS region a vertical resolution of 2.5 to 3 km has been achieved. The retrieved temperature, H<sub>2</sub>O, O<sub>3</sub>, HNO<sub>3</sub>, N<sub>2</sub>O, and relative humidity over ice are intercompared with the Microwave Limb Sounder (MLS/Aura) v2.2 data. In general, MIPAS and MLS temperatures agree within ±4 K over the whole pressure range of 316–0.68 hPa. Systematic, latitude-independent differences of −2 to −4 K (MIPAS-MLS) at 121 hPa are explained by previously observed biases in the MLS v2.2 temperature retrievals. Temperature differences of −4 K up to 12 K above 10.0 hPa are present similarly in MIPAS and MLS with respect to ECMWF (European Centre for Medium-Range Weather Forecasts) and are likely due to deficiencies of the ECMWF analysis data. MIPAS and MLS stratospheric volume mixing ratios (vmr) of H<sub>2</sub>O agree within ±1 ppmv, with indication of oscillations between 146 and 26 hPa in the MLS dataset. Tropical upper tropospheric values of relative humidity over ice measured by the two instruments differ by ±20% in the pressure range ~146 to 68 hPa. These differences are mainly caused by the MLS temperature biases. Ozone mixing ratios agree within 0.5 ppmv (10 to 20%) between 68 and 14 hPa. At pressures smaller than 10 hPa, MIPAS O<sub>3</sub> vmr are higher than MLS by an average of 0.5 ppmv (10%). General agreement between MIPAS and MLS HNO<sub>3</sub> is within the range of −1.0 (−10%) to 1.0 ppbv (20%). MIPAS HNO<sub>3</sub> is 1.0 ppbv (10%) higher compared to MLS in the height range of 46 to 10 hPa over the Northern Hemisphere. Over the tropics at 31.6 hPa MLS shows a low bias of more than 1 ppbv (>50%). In general, MIPAS and MLS N<sub>2</sub>O vmr agree within 20 to 40 ppbv (20 to 40%). Differences in the height range between 100 to 21 hPa are attributed to a known 20% positive bias in MIPAS N<sub>2</sub>O data.
Atmospheric Measurement Techniques Discussions. 01/2009;
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Dupuy E,
K. A. Walker,
Kar J,
C. D. Boone,
C. T. McElroy,
P. F. Bernath,
J. R. Drummond,
Skelton R,
S. D. McLeod,
R. C. Hughes, [......],
Urban J,
Vanhellemont F,
Vigouroux C,
T. von Clarmann,
P. von der Gathen,
C. von Savigny,
J. W. Waters,
J. C. Witte,
Wolff M,
J. M. Zawodny
[show abstract]
[hide abstract]
ABSTRACT: This paper presents extensive {bias determination} analyses of ozone observations from the Atmospheric Chemistry Experiment (ACE) satellite instruments: the ACE Fourier Transform Spectrometer (ACE-FTS) and the Measurement of Aerosol Extinction in the Stratosphere and Troposphere Retrieved by Occultation (ACE-MAESTRO) instrument. Here we compare the latest ozone data products from ACE-FTS and ACE-MAESTRO with coincident observations from nearly 20 satellite-borne, airborne, balloon-borne and ground-based instruments, by analysing volume mixing ratio profiles and partial column densities. The ACE-FTS version 2.2 Ozone Update product reports more ozone than most correlative measurements from the upper troposphere to the lower mesosphere. At altitude levels from 16 to 44 km, the average values of the mean relative differences are nearly all within +1 to +8%. At higher altitudes (45–60 km), the ACE-FTS ozone amounts are significantly larger than those of the comparison instruments, with mean relative differences of up to +40% (about +20% on average). For the ACE-MAESTRO version 1.2 ozone data product, mean relative differences are within ±10% (average values within ±6%) between 18 and 40 km for both the sunrise and sunset measurements. At higher altitudes (~35–55 km), systematic biases of opposite sign are found between the ACE-MAESTRO sunrise and sunset observations. While ozone amounts derived from the ACE-MAESTRO sunrise occultation data are often smaller than the coincident observations (with mean relative differences down to −10%), the sunset occultation profiles for ACE-MAESTRO show results that are qualitatively similar to ACE-FTS, indicating a large positive bias (mean relative differences within +10 to +30%) in the 45–55 km altitude range. In contrast, there is no significant systematic difference in bias found for the ACE-FTS sunrise and sunset measurements.
Atmospheric Chemistry and Physics 01/2009; · 4.88 Impact Factor
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[show abstract]
[hide abstract]
ABSTRACT: This paper assesses the mean differences between the two ILAS-II data versions (1.4 and 2) by comparing them with MIPAS measurements made between May and October 2003. For comparison with ILAS-II results, MIPAS data processed at the Institut für Meteorologie und Klimaforschung, Karlsruhe, Germany (IMK) in cooperation with the Instituto de Astrofísica de Andalucía (IAA) in Granada, Spain, were used. The coincidence criteria of ±300 km in space and ±12 h in time for H2O, N2O, and CH4 and the coincidence criteria of ±300 km in space and ±6 h in time for ClONO2, O3, and HNO3 were used. The ILAS-II data were separated into sunrise (= Northern Hemisphere) and sunset (= Southern Hemisphere). For the sunrise data, a clear improvement from version 1.4 to version 2 was observed for H2O, CH4, ClONO2, and O3. In particular, the ILAS-II version 1.4 mixing ratios of H2O and CH4 were unrealistically small, and those of ClONO2 above altitudes of 30 km unrealistically large. For N2O and HNO3, there were no large differences between the two versions. Contrary to the Northern Hemisphere, where some exceptional profiles deviated significantly from known climatology, no such outlying profiles were found in the Southern Hemisphere for both versions. Generally, the ILAS-II version 2 data were in better agreement with the MIPAS data than the version 1.4, and are recommended for quantitative analysis in the stratosphere. For H2O data in the Southern Hemisphere, further data quality evaluation is necessary.
Atmospheric Chemistry and Physics. 01/2008;
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G. J. Rohen,
C. V. Savigny,
J. W. Kaiser,
E. J. Llewellyn,
Froidevaux L,
López-Puertas M, Steck T,
Palm M,
Winkler H,
Sinnhuber M,
Bovensmann H,
J. P. Burrows
[show abstract]
[hide abstract]
ABSTRACT: SCIAMACHY limb scatter radiance measurements at selected wavelengths in the HARTLEY bands have been used to retrieve ozone profiles in the upper stratosphere and lower mesosphere. Comparisons with profiles measured by a ground based radiometer in Norway, MIPAS on board ENVISAT, HALOE on UARS and MLS on AURA indicate an agreement within 15% between 40 and 55 km and show that the retrieval provides reliable ozone profiles at these altitudes. Above 55 km, an increasing overestimation is observed. Beside the profile comparisons, further retrieval features of the current retrieval (version 1.26) are described.
Atmospheric Chemistry and Physics. 01/2008;
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Dupuy E,
K. A. Walker,
Kar J,
C. D. Boone,
C. T. McElroy,
P. F. Bernath,
J. R. Drummond,
Skelton R,
S. D. McLeod,
R. C. Hughes, [......],
M. B. Tully,
Urban J,
Vanhellemont F,
T. von Clarmann,
P. von der Gathen,
C. von Savigny,
J. W. Waters,
J. C. Witte,
Wolff M,
J. M. Zawodny
[show abstract]
[hide abstract]
ABSTRACT: This paper presents extensive validation analyses of ozone observations from the Atmospheric Chemistry Experiment (ACE) satellite instruments: the ACE Fourier Transform Spectrometer (ACE-FTS) and the Measurement of Aerosol Extinction in the Stratosphere and Troposphere Retrieved by Occultation (ACE-MAESTRO) instrument. The ACE satellite instruments operate in the mid-infrared and ultraviolet-visible-near-infrared spectral regions using the solar occultation technique. In order to continue the long-standing record of solar occultation measurements from space, a detailed quality assessment is required to evaluate the ACE data and validate their use for scientific purposes. Here we compare the latest ozone data products from ACE-FTS and ACE-MAESTRO with coincident observations from satellite-borne, airborne, balloon-borne and ground-based instruments, by analysing volume mixing ratio profiles and partial column densities. The ACE-FTS version 2.2 Ozone Update product reports more ozone than most correlative measurements from the upper troposphere to the lower mesosphere. At altitude levels from 16 to 44 km, the mean differences range generally between 0 and +10% with a slight but systematic positive bias (typically +5%). At higher altitudes (45–60 km), the ACE-FTS ozone amounts are significantly larger than those of the comparison instruments by up to ~40% (typically +20%). For the ACE-MAESTRO version 1.2 ozone data product, agreement within ±10% (generally better than ±5%) is found between 18 and 40 km for the sunrise and sunset measurements. At higher altitudes (45–55 km), systematic biases of opposite sign are found between the ACE-MAESTRO sunrise and sunset observations. While ozone amounts derived from the ACE-MAESTRO sunrise occultation data are often smaller than the coincident observations (by as much as −10%), the sunset occultation profiles for ACE-MAESTRO show results that are qualitatively similar to ACE-FTS and indicate a large positive bias (+10 to +30%) in this altitude range. In contrast, there is no significant difference in bias found for the ACE-FTS sunrise and sunset measurements. These systematic effects in the ozone profiles retrieved from the measurements of ACE-FTS and ACE-MAESTRO are being investigated. This work shows that the ACE instruments provide reliable, high quality measurements from the tropopause to the upper stratosphere and can be used with confidence in this vertical domain.
Atmospheric Chemistry and Physics Discussions. 01/2008;
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Cortesi U,
J C Lambert,
C De Clercq,
Bianchini G,
Blumenstock T,
Bracher A,
Castelli E,
Catoire V,
K. V. Chance,
M. De Mazière, [......],
J. J. Remedios,
Sembhi H,
Smale D, Steck T,
Taddei A,
Varotsos C,
Vigouroux C,
Waterfall A,
Wetzel G,
Wood S
[show abstract]
[hide abstract]
ABSTRACT: The Michelson Interferometer for Passive Atmospheric Sounding (MIPAS), on-board the European ENVIronmental SATellite (ENVISAT) launched on 1 March 2002, is a middle infrared Fourier Transform spectrometer measuring the atmospheric emission spectrum in limb sounding geometry. The instrument is capable to retrieve the vertical distribution of temperature and trace gases, aiming at the study of climate and atmospheric chemistry and dynamics, and at applications to data assimilation and weather forecasting. MIPAS operated in its standard observation mode for approximately two years, from July 2002 to March 2004, with scans performed at nominal spectral resolution of 0.025 cm−1 and covering the altitude range from the mesosphere to the upper troposphere with relatively high vertical resolution (about 3 km in the stratosphere). Only reduced spectral resolution measurements have been performed subsequently. MIPAS data were re-processed by ESA using updated versions of the Instrument Processing Facility (IPF v4.61 and v4.62) and provided a complete set of level-2 operational products (geo-located vertical profiles of temperature and volume mixing ratio of H2O, O3, HNO3, CH4, N2O and NO2) with quasi continuous and global coverage in the period of MIPAS full spectral resolution mission. In this paper, we report a detailed description of the validation of MIPAS-ENVISAT operational ozone data, that was based on the comparison between MIPAS v4.61 (and, to a lesser extent, v4.62) O3 VMR profiles and a comprehensive set of correlative data, including observations from ozone sondes, ground-based lidar, FTIR and microwave radiometers, remote-sensing and in situ instruments on-board stratospheric aircraft and balloons, concurrent satellite sensors and ozone fields assimilated by the European Center for Medium-range Weather Forecasting. A coordinated effort was carried out, using common criteria for the selection of individual validation data sets, and similar methods for the comparisons. This enabled merging the individual results from a variety of independent reference measurements of proven quality (i.e. well characterized error budget) into an overall evaluation of MIPAS O3 data quality, having both statistical strength and the widest spatial and temporal coverage. Collocated measurements from ozone sondes and ground-based lidar and microwave radiometers of the Network for the Detection Atmospheric Composition Change (NDACC) were selected to carry out comparisons with time series of MIPAS O3 partial columns and to identify groups of stations and time periods with a uniform pattern of ozone differences, that were subsequently used for a vertically resolved statistical analysis. The results of the comparison are classified according to synoptic and regional systems and to altitude intervals, showing a generally good agreement within the comparison error bars in the upper and middle stratosphere. Significant differences emerge in the lower stratosphere and are only partly explained by the larger contributions of horizontal and vertical smoothing differences and of collocation errors to the total uncertainty. Further results obtained from a purely statistical analysis of the same data set from NDACC ground-based lidar stations, as well as from additional ozone soundings at middle latitudes and from NDACC ground-based FTIR measurements, confirm the validity of MIPAS O3 profiles down to the lower stratosphere, with evidence of larger discrepancies at the lowest altitudes. The validation against O3 VMR profiles using collocated observations performed by other satellite sensors (SAGE II, POAM III, ODIN-SMR, ACE-FTS, HALOE, GOME) and ECMWF assimilated ozone fields leads to consistent results, that are to a great extent compatible with those obtained from the comparison with ground-based measurements. Excellent agreement in the full vertical range of the comparison is shown with respect to collocated ozone data from stratospheric aircraft and balloon instruments, that was mostly obtained in very good spatial and temporal coincidence with MIPAS scans. This might suggest that the larger differences observed in the upper troposphere and lowermost stratosphere with respect to collocated ground-based and satellite O3 data are only partly due to a degradation of MIPAS data quality. They should be rather largely ascribed to the natural variability of these altitude regions and to other components of the comparison errors. By combining the results of this large number of validation data sets we derived a general assessment of MIPAS v4.61 and v4.62 ozone data quality. A clear indication of the validity of MIPAS O3 vertical profiles is obtained for most of the stratosphere, where the mean relative difference with the individual correlative data sets is always lower than ±10%. Furthermore, these differences always fall within the combined systematic error (from 1 hPa to 50 hPa) and the standard deviation is fully consistent with the random error of the comparison (from 1 hPa to ~30–40 hPa). A degradation in the quality of the agreement is generally observed in the lower stratosphere and upper troposphere, with biases up to 25% at 100 hPa and standard deviation of the global mean differences up to three times larger than the combined random error in the range 50–100 hPa. The larger differences observed at the bottom end of MIPAS retrieved profiles can be associated, as already noticed, to the effects of stronger atmospheric gradients in the UTLS that are perceived differently by the various measurement techniques. However, further components that may degrade the results of the comparison at lower altitudes can be identified as potentially including cloud contamination, which is likely not to have been fully filtered using the current settings of the MIPAS cloud detection algorithm, and in the linear approximation of the forward model that was used for the a priori estimate of systematic error components. The latter, when affecting systematic contributions with a random variability over the spatial and temporal scales of global averages, might result in an underestimation of the random error of the comparison and add up to other error sources, such as the possible underestimates of the p and T error propagation based on the assumption of a 1 K and 2% uncertainties, respectively, on MIPAS temperature and pressure retrievals. At pressure lower than 1 hPa, only a small fraction of the selected validation data set provides correlative ozone data of adequate quality and it is difficult to derive quantitative conclusions about the performance of MIPAS O3 retrieval for the topmost layers.
Atmospheric Chemistry and Physics 09/2007; 7:4807-4867. · 4.88 Impact Factor
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Höpfner M,
T. von Clarmann,
Fischer H,
Funke B,
Glatthor N,
Grabowski U,
Kellmann S,
Kiefer M,
Linden A,
Milz M, [......],
Reddmann T,
Ruhnke R,
Schneider M,
Strandberg A,
Toon G,
K. A. Walker,
Warneke T,
Wetzel G,
Wood S,
Zander R
[show abstract]
[hide abstract]
ABSTRACT: Altitude profiles of ClONO<sub>2</sub> retrieved with the IMK (Institut für Meteorologie und Klimaforschung) science-oriented data processor from MIPAS/Envisat (Michelson Interferometer for Passive Atmospheric Sounding on Envisat) mid-infrared limb emission measurements between July 2002 and March 2004 have been validated by comparison with balloon-borne (Mark IV, FIRS2, MIPAS-B), airborne (MIPAS-STR), ground-based (Spitsbergen, Thule, Kiruna, Harestua, Jungfraujoch, Izaña, Wollongong, Lauder), and spaceborne (ACE-FTS) observations. With few exceptions we found very good agreement between these instruments and MIPAS with no evidence for any bias in most cases and altitude regions. For balloon-borne measurements typical absolute mean differences are below 0.05 ppbv over the whole altitude range from 10 to 39 km. In case of ACE-FTS observations mean differences are below 0.03 ppbv for observations below 26 km. Above this altitude the comparison with ACE-FTS is affected by the photochemically induced diurnal variation of ClONO<sub>2</sub>. Correction for this by use of a chemical transport model led to an overcompensation of the photochemical effect by up to 0.1 ppbv at altitudes of 30–35 km in case of MIPAS-ACE-FTS comparisons while for the balloon-borne observations no such inconsistency has been detected. The comparison of MIPAS derived total column amounts with ground-based observations revealed no significant bias in the MIPAS data. Mean differences between MIPAS and FTIR column abundances are 0.11±0.12×10<sup>14</sup> cm<sup>−2</sup> (1.0±1.1%) and −0.09±0.19×10<sup>14</sup> cm<sup>−2</sup> (−0.8±1.7%), depending on the coincidence criterion applied. χ<sup>2</sup> tests have been performed to assess the combined precision estimates of MIPAS and the related instruments. When no exact coincidences were available as in case of MIPAS – FTIR or MIPAS – ACE-FTS comparisons it has been necessary to take into consideration a coincidence error term to account for χ<sup>2</sup> deviations. From the resulting χ<sup>2</sup> profiles there is no evidence for a systematic over/underestimation of the MIPAS random error analysis.
Atmospheric Chemistry and Physics. 01/2007;
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D. Y. Wang,
Höpfner M,
G. Mengistu Tsidu,
G. P. Stiller,
T. von Clarmann,
Fischer H,
Blumenstock T,
Glatthor N,
Grabowski U,
Hase F, [......],
Irie H,
Urban J,
Murtagh D,
M. L. Santee,
Toon G,
M. R. Gunson,
F. W. Irion,
C. D. Boone,
Walker K,
P. F. Bernath
[show abstract]
[hide abstract]
ABSTRACT: The Michelson Interferometer for Passive Atmospheric Sounding (MIPAS) onboard the ENVISAT satellite provides profiles of temperature and various trace-gases from limb-viewing mid-infrared emission measurements. The stratospheric nitric acid (HNO<sub>3</sub>) from September 2002 to March 2004 was retrieved from the MIPAS observations using the science-oriented data processor developed at the Institut für Meteorologie und Klimaforschung (IMK), which is complemented by the component of non-local thermodynamic equilibrium (non-LTE) treatment from the Instituto de Astrofísica de Andalucía (IAA). The IMK-IAA research product, different from the ESA operational product, is validated in this paper by comparison with a number of reference data sets. Individual HNO<sub>3</sub> profiles of the IMK-IAA MIPAS show good agreement with those of the balloon-borne version of MIPAS (MIPAS-B) and the infrared spectrometer MkIV, with small differences of less than 0.5 ppbv throughout the entire altitude range up to about 38 km, and below 0.2 ppbv above 30 km. However, the degree of consistency is largely affected by their temporal and spatial coincidence, and differences of 1 to 2 ppbv may be observed between 22 and 26 km at high latitudes near the vortex boundary, due to large horizontal inhomogeneity of HNO<sub>3</sub>. Statistical comparisons of MIPAS IMK-IAA HNO<sub>3</sub> VMRs with respect to those of satellite measurements of Odin/SMR, ILAS-II, ACE-FTS, as well as the MIPAS ESA product show good consistency. The mean differences are generally ±0.5 ppbv and standard deviations of the differences are of 0.5 to 1.5 ppbv. The maximum differences are 2.0 ppbv around 20 to 25 km. This gives confidence in the general reliability of MIPAS HNO<sub>3</sub> VMR data and the other three satellite data sets.
Atmospheric Chemistry and Physics. 01/2007;
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Steck T,
T. von Clarmann,
Fischer H,
Funke B,
Glatthor N,
Grabowski U,
Höpfner M,
Kellmann S,
Kiefer M,
Linden A, [......],
Oelhaf H,
Raffalski U,
A. Redondas Marrero,
Remsberg E,
J. Russell III,
Stebel K,
Steinbrecht W,
Wetzel G,
Yela M,
Zhang G
[show abstract]
[hide abstract]
ABSTRACT: This paper characterizes vertical ozone profiles retrieved with the IMK-IAA (Institute for Meteorology and Climate Research, Karlsruhe – Instituto de Astrofisica de Andalucia) science-oriented processor from high spectral resolution data (until March 2004) measured by the Michelson Interferometer for Passive Atmospheric Sounding (MIPAS) aboard the environmental satellite Envisat. Bias determination and precision validation is performed on the basis of correlative measurements by ground-based lidars, Fourier transform infrared spectrometers, and microwave radiometers as well as balloon-borne ozonesondes, the balloon-borne version of MIPAS, and two satellite instruments (Halogen Occultation Experiment and Polar Ozone and Aerosol Measurement III). Percentage mean differences between MIPAS and the comparison instruments for stratospheric ozone are generally within ±10%. The precision in this altitude region is estimated at values between 5 and 10% which gives an accuracy of 15 to 20%. Below 18 km, the spread of the percentage mean differences is larger and the precision degrades to values of more than 20% depending on altitude and latitude. The main reason for the degraded precision at low altitudes is attributed to undetected thin clouds which affect MIPAS retrievals, and to the influence of uncertainties in the water vapor concentration.
Atmospheric Chemistry and Physics. 01/2007;
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Hocke K,
Kämpfer N,
Ruffieux D,
Froidevaux L,
Parrish A,
Boyd I,
T. von Clarmann, Steck T,
Y. M. Timofeyev,
A. V. Polyakov,
Kyrölä E
[show abstract]
[hide abstract]
ABSTRACT: Stratospheric O3 profiles obtained by the satellite limb sounders Aura/MLS, ENVISAT/MIPAS, ENVISAT/GOMOS, SAGE-II, SAGE-III, UARS/HALOE are compared to coincident O3 profiles of the ground-based microwave radiometer SOMORA in Switzerland. Data from the various measurement techniques are within 10% at altitudes below 45 km. At altitudes 45–60 km, the relative O3 differences are within a range of 50%. Larger deviations at upper altitudes are attributed to larger relative measurement errors caused by lower O3 concentrations. The spatiotemporal characteristics of the O3 differences (satellite – ground station) are investigated by analyzing about 2300 coincident profile pairs of Aura/MLS (retrieval version 1.5) and SOMORA. The probability density function of the O3 differences is represented by a Gaussian normal distribution. The dependence of the O3 differences on the horizontal distance between the sounding volumes of Aura/MLS and SOMORA is derived. While the mean bias (Aura/MLS – SOMORA) is constant with increasing horizontal distance (up to 800 km), the standard deviation of the O3 differences increases from around 8 to 11% in the mid-stratosphere. Geographical maps yield azimuthal dependences and horizontal gradients of the O3 difference field around the SOMORA ground station. Coherent oscillations of O3 are present in the time series of Aura/MLS and SOMORA (e.g., due to traveling planetary waves). Ground- and space-based measurements often complement one another. We discuss the double differencing technique which allows both the cross-validation of two satellites by means of a ground station and the cross-validation of distant ground stations by means of one satellite. Temporal atmospheric noise in the geographical ozone map over Payerne is significantly reduced by combination of the data from SOMORA and Aura/MLS. These analyses illustrate the synergy of ground-based and space-based measurements.
Atmospheric Chemistry and Physics. 01/2007;
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T. von Clarmann,
Glatthor N,
M. E. Koukouli,
G. P. Stiller,
Funke B,
Grabowski U,
Höpfner M,
Kellmann S,
Linden A,
Milz M, Steck T,
Fischer H
[show abstract]
[hide abstract]
ABSTRACT: Under cloud free conditions, the Michelson Interferometer for Passive Atmospheric Sounding (MIPAS) provides measurements of spectrally resolved limb radiances down to the upper troposphere. These are used to infer global distributions of mixing ratios of atmospheric constituents in the upper troposphere and the stratosphere. From 21 October to 12 November 2003, MIPAS observed enhanced amounts of upper tropospheric C<sub>2</sub>H<sub>6</sub> (up to about 400 pptv) and ozone (up to about 80 ppbv). The absolute values of C<sub>2</sub>H<sub>6</sub>, however, may be systematically low by about 30% due to uncertainties of the spectroscopic data used. By means of trajectory calculations, the enhancements observed in the southern hemisphere are, at least partly, attributed to a biomass burning plume, which covers wide parts of the Southern hemisphere, from South America, the Atlantic Ocean, Africa, the Indian Ocean to Australia. The chemical composition of the part of the plume-like pollution belt associated with South American fires, where rainforest burning is predominant appears different from the part of the plume associated with southern African savanna burning. In particular, African savanna fires lead to a larger ozone enhancement than equatorial American fires. In this analysis, MIPAS observations of high ozone were disregarded where low CFC-11 (below 245 pptv) was observed, because this hints at a stratospheric component in the measured signal. Different type of vegetation burning (flaming versus smouldering combustion) has been identified as a candidate explanation for the different plume compositions.
Atmospheric Chemistry and Physics. 01/2007;
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Hocke K,
Kämpfer N,
Ruffieux D,
Froidevaux L,
Parrish A,
Boyd I,
T. von Clarmann, Steck T,
Timofeyev Y.M,
Polyakov A.V,
Kyrölä E
[show abstract]
[hide abstract]
ABSTRACT: Stratospheric O3 profiles obtained by the satellite limb sounders Aura/MLS, ENVISAT/MIPAS, ENVISAT/GOMOS, SAGE-II, SAGE-III, UARS/HALOE are compared to coincident O3 profiles of the ground-based microwave radiometer SOMORA in Switzerland. Data from the various measurement techniques are within 10% at altitudes below 45 km. At altitudes 45–60 km, the relative O3 differences are within a range of 50% Larger deviations at upper altitudes are attributed to larger relative measurement errors caused by lower O3 concentrations. The spatiotemporal characteristics of the O3 differences (satellite – ground station) are investigated by analyzing about 5000 coincident profile pairs of Aura/MLS (retrieval version 1.5) and SOMORA. The probability density function of the O3 differences is represented by a Gaussian normal distribution (except for profile pairs around the stratopause at noon). The dependence of the O3 differences on the horizontal distance between the sounding volumes of Aura/MLS and SOMORA is derived. While the mean bias (Aura/MLS – SOMORA) is constant with increasing horizontal distance (up to 800 km), the standard deviation of the O3 differences increases from around 8 to 12% in the mid-stratosphere. Geographical maps yield azimuthal dependences and horizontal gradients of the O3 difference field around the SOMORA ground station. Coherent oscillations of O3 are present in the time series of Aura/MLS and SOMORA (e.g., due to traveling planetary waves). Ground- and space-based measurements often complement one another. We introduce the double differencing technique which allows both the cross-validation of two satellites by means of a ground station and the cross-validation of distant ground stations by means of one satellite. Temporal atmospheric noise in the geographical ozone map over Payerne is significantly reduced by combination of the data from SOMORA and Aura/MLS. These analyses illustrate the synergy between ground-based and space-based measurements.
Atmospheric Chemistry and Physics Discussions. 01/2007;
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G. J. Rohen,
C. V. Savigny,
J. W. Kaiser,
E. J. Llewellyn,
Froidevaux L,
López-Puertas M, Steck T,
Palm M,
Winkler H,
J. P. Burrows,
Sinnhuber M,
Bovensmann H
[show abstract]
[hide abstract]
ABSTRACT: SCIAMACHY limb scatter spectra have been used to retrieve atmospheric ozone profiles in the upper stratosphere and lower mesosphere. Through a selection of the wavelengths in the HARTLEY bands of ozone, profiles extending to 60 or 70 km altitude were retrieved. This constitutes the highest possible ozone profile information retrieval using the backscatter technique. Comparisons with profiles measured by a ground based radiometer in Norway, MIPAS on board ENVISAT, HALOE on UARS and MLS on AURA indicate a good agreement of the ozone profiles in the upper stratosphere within 10% but also an increasing overestimation above 50 to 55 km. Sensitivity studies show that solar zenith uncertainty and tangent height errors are the largest error sources. Although the tangent height is corrected through an own retrieval the correction seemed to be be worser with increasing altitude and remains therefore as the largest error source for this presented profile retrieval.
Atmospheric Chemistry and Physics Discussions. 01/2007;
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Steck T,
Glatthor N,
T. von Clarmann,
Fischer H,
J.-M. Flaud,
Funke B,
Grabowski U,
Höpfner M,
Kellmann S,
Linden A,
Perrin A,
G. P. Stiller
[show abstract]
[hide abstract]
ABSTRACT: The Fourier transform spectrometer MIPAS (Michelson Interferometer for Passive Atmospheric Sounding) on Envisat measures infrared emission of the Earth's atmosphere in a limb viewing mode. High spectral resolution measurements of MIPAS are sensitive to formaldehyde from the upper troposphere to the stratopause. Formaldehyde single profile retrieval is formally possible, however with a large noise error (more than 60%), which is the dominant error source. The number of degrees of freedom for single profile retrieval ranges from 2 to 4.5 depending on latitude and number of cloud-free tangent altitudes. Calculation of zonal mean values for 30 days of data during 8 September 2003 and 1 December 2003 reduces the noise induced error by a factor of 20 or more. In the upper tropical troposphere zonal mean values of about 70 parts per trillion by volume (pptv) were found, which have been attributed to biomass burning emissions. In the stratosphere, formaldehyde values are determined by photochemical reactions. In the upper tropical stratosphere, formaldehyde zonal mean maximum values can reach 130 pptv. Diurnal variations in this region can be up to 50 pptv. Comparisons with other satellite instruments show generally good agreement in the region of upper troposphere and lower stratosphere as well as in the upper stratosphere.
Atmospheric Chemistry and Physics Discussions. 01/2007;
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G. P. Stiller,
T. von Clarmann,
Höpfner M,
Glatthor N,
Grabowski U,
Kellmann S,
Kleinert A,
Linden A,
Milz M,
Reddmann T, Steck T,
Fischer H,
Funke B,
López-Puertas M,
Engel A
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ABSTRACT: Global distributions of profiles of sulphur hexafluoride (SF<sub>6</sub>) have been retrieved from limb emission spectra recorded by the Michelson Interferometer for Passive Atmospheric Sounding (MIPAS) on Envisat covering the period September 2002 to March 2004. Individual SF<sub>6</sub> profiles have a precision of 0.5 pptv below 25 km altitude and a vertical resolution of 4–6 km up to 35 km altitude. These data have been validated versus in situ observations obtained during balloon flights of a cryogenic whole-air sampler. For the tropical troposphere a trend of 0.227±0.008 pptv/yr has been derived from the MIPAS data, which is in excellent agreement with the trend from ground-based flask and in situ measurements from the National Oceanic and Atmospheric Administration Earth System Research Laboratory, Global Monitoring Division. For the data set currently available, based on at least three days of data per month, monthly 5° latitude mean values have a 1σ standard error of 1%. From the global SF<sub>6</sub> distributions, global daily and monthly distributions of the apparent mean age of air are inferred by application of the tropical tropospheric trend derived from MIPAS data. The inferred mean ages are provided for the full globe up to 90° N/S, and have a 1σ standard error of 0.25 yr. They range between 0 (near the tropical tropopause) and 7 years (except for situations of mesospheric intrusions) and agree well with earlier observations. The seasonal variation of the mean age of stratospheric air indicates episodes of severe intrusion of mesospheric air during each Northern and Southern polar winter observed, long-lasting remnants of old, subsided polar winter air over the spring and summer poles, and a rather short period of mixing with midlatitude air and/or upward transport during fall in October/November (NH) and April/May (SH), respectively, with small latitudinal gradients, immediately before the new polar vortex starts to form. The mean age distributions further confirm that SF<sub>6</sub> is destroyed in the mesosphere to a considerable amount. Model calculations with the Karlsruhe simulation model of the middle atmosphere (KASIMA) chemical transport model agree well with observed global distributions of the mean age only if the SF<sub>6</sub> sink reactions in the mesosphere are included in the model.
Atmospheric Chemistry and Physics Discussions. 01/2007;
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Glatthor N,
T. von Clarmann,
Fischer H,
Funke B,
Gil-López S,
Grabowski U,
Höpfner M,
Kellmann S,
Linden A,
López-Puertas M,
G. Mengistu Tsidu,
Milz M, Steck T,
G. P. Stiller,
Wang D.-Y
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ABSTRACT: We report on the dependence of ozone volume mixing ratio profiles, retrieved from limb emission infrared spectra of the Michelson Interferometer for Passive Atmospheric Sounding (MIPAS), on different retrieval setups such as the treatment of the background continuum, cloud filtering, spectral regions used for analysis and a series of further more technical parameter choices. The purpose of this investigation is to better understand the error sources of the ozone retrieval, to optimize the current retrieval setup and to document changes in the data versions. It was shown that the cloud clearing technique used so far (cloud index 1.8) does not reliably exclude all cloud-contaminated spectra from analysis. Through analysis of spectra calculated for cloudy atmospheres we found that the cloud index should be increased to a value of 3.0 or higher. Further, it was found that assignment of a common background continuum to adjacent microwindows within 5 cm<sup>−1</sup> is advantageous, because it sufficiently represents the continuum emission by aerosols, clouds and gases as reported in the literature, and is computationally more efficient. For ozone retrieval we use ozone lines from MIPAS band A (685–970 cm<sup>−1</sup>) and band AB (1020–1170 cm<sup>−1</sup>) as well. Therefore we checked ozone retrievals with lines from bands A or AB only for a systematic difference. Such a difference was indeed found and could, to a major part, be attributed to the spectroscopic data used in these two bands, and to a minor part to neglection of modelling of non-local thermodynamic (non-LTE) emissions. Another potential explanation, a bias in the radiance calibration of level-1B spectra of bands A and AB, could largely be ruled out by correlation analysis and inspection of broadband spectra. Further upgrades in the ozone retrieval consist of application of an all-zero a-priori profile and a weaker regularization. Finally, the ozone distribution obtained with the new retrieval setup (data versions V3o_O3_7) was compared to the data version used before (V2_O3_2). Differences are smaller than $pm$0.4 ppmv in the altitude region 15–50 km. Further, differences to ozone measured by the HALogen Occultation Experiment (HALOE) on the Upper Atmospheric Research Satellite (UARS) are partly reduced with the new MIPAS data version.
Atmospheric Chemistry and Physics. 01/2006;
