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  • 1
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    Online Resource
    Mixing Processes during the Antarctic Vortex Split in September–October 2002 as Inferred from Source Gas and Ozone Distributions from ENVISAT–MIPAS
    American Meteorological Society ; 2005
    In:  Journal of the Atmospheric Sciences Vol. 62, No. 3 ( 2005-03-01), p. 787-800
    Details
    In: Journal of the Atmospheric Sciences, American Meteorological Society, Vol. 62, No. 3 ( 2005-03-01), p. 787-800
    Abstract: In late September 2002, an Antarctic major stratospheric warming occurred, which led to a strong distortion of the southern polar vortex and to a split of its mid- and upper-stratospheric parts. Such an event had never before been observed since the beginning of regular Antarctic stratospheric temperature observations in the 1950s. The split is studied by means of nonoperational level-2 CH4, N2O, CFC-11, and O3 data, retrieved at the Institute for Meteorology and Climate Research Karlsruhe (IMK) from high-resolution atmospheric limb emission spectra from the Michelson Interferometer for Passive Atmospheric Sounding (MIPAS) on board the European research satellite, Environmental Satellite (ENVISAT). Retrieved horizontal and vertical distributions of CH4 and N2O show good consistency with potential vorticity fields of the European Centre for Medium-Range Weather Forecasts (ECMWF) analysis for the entire period under investigation, even for fine structures such as vortex filaments. Tracer correlation analysis suggests that mixing into the vortex had already occurred before the major warming and that vortex fragments were transported into the surrounding air masses on potential temperature levels above 400 K during the split. Correlation analysis of ozone with the source gases indicates slight ongoing ozone destruction in the lower-stratospheric vortex (below ∼500 K) after the beginning of the warming event.
    Type of Medium: Online Resource
    ISSN: 1520-0469 , 0022-4928
    URL: Article
    DOI: 10.1175/JAS-3332.1
    RVK:
    UA 4800
    Language: English
    Publisher: American Meteorological Society
    Publication Date: 2005
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  • 2
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    Spatial and temporal variability of summer rainfall over Ethiopia from observations and a regional climate model experiment
    Springer Science and Business Media LLC ; 2013
    In:  Theoretical and Applied Climatology Vol. 111, No. 3-4 ( 2013-2), p. 665-681
    Details
    In: Theoretical and Applied Climatology, Springer Science and Business Media LLC, Vol. 111, No. 3-4 ( 2013-2), p. 665-681
    Type of Medium: Online Resource
    ISSN: 0177-798X , 1434-4483
    URL: Article
    DOI: 10.1007/s00704-012-0700-4
    RVK:
    RA 1000
    Language: English
    Publisher: Springer Science and Business Media LLC
    Publication Date: 2013
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  • 3
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    Retrieval of stratospheric ozone profiles from MIPAS/ENVISAT limb emission spectra: a sensitivity study
    Copernicus GmbH ; 2006
    In:  Atmospheric Chemistry and Physics Vol. 6, No. 10 ( 2006-07-07), p. 2767-2781
    Details
    In: Atmospheric Chemistry and Physics, Copernicus GmbH, Vol. 6, No. 10 ( 2006-07-07), p. 2767-2781
    Abstract: 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−1 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−1) and band AB (1020–1170 cm−1) 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 ±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.
    Type of Medium: Online Resource
    ISSN: 1680-7324
    URL: Article
    DOI: 10.5194/acp-6-2767-2006
    Language: English
    Publisher: Copernicus GmbH
    Publication Date: 2006
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  • 4
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    Water vapor distributions measured with the Michelson Interferometer for Passive Atmospheric Sounding on board Envisat (MIPAS/Envisat)
    American Geophysical Union (AGU) ; 2005
    In:  Journal of Geophysical Research Vol. 110, No. D24 ( 2005)
    Details
    In: Journal of Geophysical Research, American Geophysical Union (AGU), Vol. 110, No. D24 ( 2005)
    Type of Medium: Online Resource
    ISSN: 0148-0227
    URL: Article
    DOI: 10.1029/2005JD005973
    Language: English
    Publisher: American Geophysical Union (AGU)
    Publication Date: 2005
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  • 5
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    Validation of nitric acid retrieved by the IMK-IAA processor from MIPAS/ENVISAT measurements
    Copernicus GmbH ; 2007
    In:  Atmospheric Chemistry and Physics Vol. 7, No. 3 ( 2007-02-14), p. 721-738
    Details
    In: Atmospheric Chemistry and Physics, Copernicus GmbH, Vol. 7, No. 3 ( 2007-02-14), p. 721-738
    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 (HNO3) 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 HNO3 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 HNO3. Statistical comparisons of MIPAS IMK-IAA HNO3 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 HNO3 VMR data and the other three satellite data sets.
    Type of Medium: Online Resource
    ISSN: 1680-7324
    URL: Article
    DOI: 10.5194/acp-7-721-2007
    Language: English
    Publisher: Copernicus GmbH
    Publication Date: 2007
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  • 6
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    High-Resolution Monthly Rainfall Database for Ethiopia: Homogenization, Reconstruction, and Gridding
    American Meteorological Society ; 2012
    In:  Journal of Climate Vol. 25, No. 24 ( 2012-12-15), p. 8422-8443
    Details
    In: Journal of Climate, American Meteorological Society, Vol. 25, No. 24 ( 2012-12-15), p. 8422-8443
    Abstract: Recent heightened concern regarding possible consequences of anthropogenically induced global warming has spurred analyses of data aimed at detection of climate change and more thorough characterization of the natural climate variability. However, there is greater concern regarding the extent and especially quality of the historical climate data. In this paper, rainfall records of 233 gauge stations over Ethiopia for the 1978–2007 period are employed in an analysis that involves homogenization, reconstruction, and gridding onto a regular 0.5° × 0.5° resolution grid. Inhomogeneity is detected and adjusted based on quantile matching. The regularized expectation-maximization and multichannel singular spectrum analysis algorithms are then utilized for imputation of missing values, and the latter has been determined to have a marginal advantage. Ordinary kriging is used to create a gridded monthly rainfall dataset. The spatial and temporal coherence of this dataset are assessed using harmonic analysis, self-organizing maps, and intercomparison with global datasets. The self-organizing map delineates Ethiopia into nine homogeneous rainfall regimes, which is consistent with seasonal and interannual rainfall variations. The harmonic analysis of the dataset reveals that the annual mode accounts for 55%–85% of the seasonal rainfall variability over western Ethiopia while the semiannual mode accounts for up to 40% over southern Ethiopia. The dataset is also intercompared with Global Precipitation Climatology Project (GPCP), Climate Prediction Center (CPC) Merged Analysis of Precipitation (CMAP), Climatic Research Unit time series version 3 (CRUTS3.0), Tropical Rainfall Measuring Mission (TRMM), and interim ECMWF Re-Analysis (ERA-Interim) rainfall. The correlation of the dataset with global datasets ranges from 0.52 to 0.95 over sparse to dense rain gauge regions. The GPCP rainfall has a small bias and good correlation with the new dataset whereas TRMM and ERA-Interim have relatively large dry and wet biases, respectively.
    Type of Medium: Online Resource
    ISSN: 0894-8755 , 1520-0442
    URL: Article
    DOI: 10.1175/JCLI-D-12-00027.1
    RVK:
    UA 4548
    Language: English
    Publisher: American Meteorological Society
    Publication Date: 2012
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  • 7
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    Aerosol climatology over South Africa based on 10 years of Multiangle Imaging Spectroradiometer (MISR) data
    American Geophysical Union (AGU) ; 2011
    In:  Journal of Geophysical Research Vol. 116, No. D20 ( 2011-10-29)
    Details
    In: Journal of Geophysical Research, American Geophysical Union (AGU), Vol. 116, No. D20 ( 2011-10-29)
    Type of Medium: Online Resource
    ISSN: 0148-0227
    URL: Article
    DOI: 10.1029/2011JD016023
    Language: English
    Publisher: American Geophysical Union (AGU)
    Publication Date: 2011
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  • 8
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    Evaluation of Regional Climatic Model Simulated Aerosol Optical Properties over South Africa Using Ground-Based and Satellite Observations
    Hindawi Limited ; 2013
    In:  ISRN Atmospheric Sciences Vol. 2013 ( 2013-11-10), p. 1-17
    Details
    In: ISRN Atmospheric Sciences, Hindawi Limited, Vol. 2013 ( 2013-11-10), p. 1-17
    Abstract: The present study evaluates the aerosol optical property computing performance of the Regional Climate Model (RegCM4) which is interactively coupled with anthropogenic-desert dust schemes, in South Africa. The validation was carried out by comparing RegCM4 estimated: aerosol extinction coefficient profile, Aerosol Optical Depth (AOD), and Single Scattering Albedo (SSA) with AERONET, LIDAR, and MISR observations. The results showed that the magnitudes of simulated AOD at the Skukuza station (24°S, 31°E) are within the standard deviation of AERONET and ±25% of MISR observations. Within the latitudinal range of 26.5°S to 24.5°S, simulated AOD and SSA values are within the standard deviation of MISR retrievals. However, within the latitude range of 33.5°S to 27°S, the model exhibited enhanced AOD and SSA values when compared with MISR observations. This is primarily associated with the dry bias in simulated precipitation that leads to the overestimation of dust emission and underestimation of aerosol wet deposition. With respect to LIDAR, the model performed well in capturing the major aerosol extinction profiles. Overall, the results showed that RegCM4 has a good ability in reproducing the major observational features of aerosol optical fields over the area of interest.
    Type of Medium: Online Resource
    ISSN: 2314-4645
    URL: Article
    DOI: 10.1155/2013/237483
    Language: English
    Publisher: Hindawi Limited
    Publication Date: 2013
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  • 9
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    HNO 3 , N 2 O 5 , and ClONO 2 enhancements after the October-November 2003 solar proton events : NO y ENHANCEMENTS AFTER SOLAR PROTON EVENTS
    American Geophysical Union (AGU) ; 2005
    In:  Journal of Geophysical Research: Space Physics Vol. 110, No. A9 ( 2005-09)
    Details
    In: Journal of Geophysical Research: Space Physics, American Geophysical Union (AGU), Vol. 110, No. A9 ( 2005-09)
    Type of Medium: Online Resource
    ISSN: 0148-0227
    URL: Article
    DOI: 10.1029/2005JA011051
    Language: English
    Publisher: American Geophysical Union (AGU)
    Publication Date: 2005
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    detail.hit.zdb_id: 3094268-8
    detail.hit.zdb_id: 710256-2
    detail.hit.zdb_id: 2016804-4
    detail.hit.zdb_id: 3094181-7
    detail.hit.zdb_id: 3094219-6
    detail.hit.zdb_id: 3094167-2
    detail.hit.zdb_id: 2220777-6
    detail.hit.zdb_id: 3094197-0
    SSG: 16,13
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  • 10
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    Retrieval and satellite intercomparison of O〈sub〉3〈/sub〉 measurements from ground-based FTIR Spectrometer at Equatorial Station: Addis Ababa, Ethiopia
    Copernicus GmbH ; 2013
    In:  Atmospheric Measurement Techniques Vol. 6, No. 2 ( 2013-02-28), p. 495-509
    Details
    In: Atmospheric Measurement Techniques, Copernicus GmbH, Vol. 6, No. 2 ( 2013-02-28), p. 495-509
    Abstract: Abstract. Since May 2009, high-resolution Fourier Transform Infrared (FTIR) solar absorption spectra have been recorded at Addis Ababa (9.01° N latitude, 38.76° E longitude, 2443 m altitude above sea level), Ethiopia. The vertical profiles and total column amounts of ozone (O3) are deduced from the spectra by using the retrieval code PROFFIT (V9.5) and regularly determined instrumental line shape (ILS). A detailed error analysis of the O3 retrieval is performed. Averaging kernels of the target gas shows that the major contribution to the retrieved information comes from the measurement. The degrees of freedom for signals is found to be 2.1 on average for the retrieval of O3 from the observed FTIR spectra. The ozone Volume Mixing Ratio (VMR) profiles and column amounts retrieved from FTIR spectra are compared with the coincident satellite observations of Microwave Limb Sounding (MLS), Michelson Interferometer for Passive Atmospheric Sounding (MIPAS), Tropospheric Emission Spectrometer (TES), Ozone Monitoring Instrument (OMI), Atmospheric Infrared Sounding (AIRS) and Global Ozone Monitoring Experiment (GOME-2) instruments. The mean relative differences in ozone profiles of FTIR from MLS and MIPAS are generally lower than 15% within the altitude range of 27 to 36 km, whereas difference from TES is lower than 1%. Comparisons of measurements of column amounts from the satellite and the ground-based FTIR show very good agreement as exhibited by relative differences within +0.2% to +2.8% for FTIR versus MLS and GOME-2; and −0.9 to −9.0% for FTIR versus OMI, TES and AIRS. The corresponding standard deviations are within 2.0 to 2.8% for FTIR versus MLS and GOME-2 comparisons whereas that of FTIR versus OMI, TES and AIRS are within 3.5 to 7.3%. Thus, the retrieved O3 VMR and column amounts from a tropical site, Addis Ababa, is found to exhibit very good agreement with all coincident satellite observations over an approximate 3-yr period.
    Type of Medium: Online Resource
    ISSN: 1867-8548
    URL: Article
    DOI: 10.5194/amt-6-495-2013
    Language: English
    Publisher: Copernicus GmbH
    Publication Date: 2013
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