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Volume 11, issue 9 | Copyright

Special issue: Towards Unified Error Reporting (TUNER)

Atmos. Meas. Tech., 11, 4981-5006, 2018
https://doi.org/10.5194/amt-11-4981-2018
© Author(s) 2018. This work is distributed under
the Creative Commons Attribution 4.0 License.

Research article 04 Sep 2018

Research article | 04 Sep 2018

Evaluation of MUSICA IASI tropospheric water vapour profiles using theoretical error assessments and comparisons to GRUAN Vaisala RS92 measurements

Christian Borger1,a, Matthias Schneider1, Benjamin Ertl1,2, Frank Hase1, Omaira E. García3, Michael Sommer4, Michael Höpfner1, Stephen A. Tjemkes5, and Xavier Calbet6 Christian Borger et al.
  • 1Institute of Meteorology and Climate Research (IMK-ASF), Karlsruhe Institute of Technology, Karlsruhe, Germany
  • 2Steinbuch Centre for Computing (SCC), Karlsruhe Institute of Technology, Karlsruhe, Germany
  • 3Izaña Atmospheric Research Center, Agencia Estatal de Meteorología (AEMET), Santa Cruz de Tenerife, Spain
  • 4Deutscher Wetterdienst, Meteorologisches Observatorium Lindenberg, Richard-Aßmann-Observatorium, Am Observatorium 12, 15848 Lindenberg/Tauche, Germany
  • 5EUMETSAT, Eumetsat Allee 1, 64295 Darmstadt, Germany
  • 6AEMET, C/Leonardo Prieto Castro 8, Ciudad Universitaria, 28071 Madrid, Spain
  • anow at: Satellite Remote Sensing Group, Max Planck Institute for Chemistry, Mainz, Germany

Abstract. Volume mixing ratio water vapour profiles have been retrieved from IASI (Infrared Atmospheric Sounding Interferometer) spectra using the MUSICA (MUlti-platform remote Sensing of Isotopologues for investigating the Cycle of Atmospheric water) processor. The retrievals are done for IASI observations that coincide with Vaisala RS92 radiosonde measurements performed in the framework of the GCOS (Global Climate Observing System) Reference Upper-Air Network (GRUAN) in three different climate zones: the tropics (Manus Island, 2°S), mid-latitudes (Lindenberg, 52°N), and polar regions (Sodankylä, 67°N).

The retrievals show good sensitivity with respect to the vertical H2O distribution between 1km above ground and the upper troposphere. Typical DOFS (degrees of freedom for signal) values are about 5.6 for the tropics, 5.1 for summertime mid-latitudes, 3.8 for wintertime mid-latitudes, and 4.4 for summertime polar regions. The errors of the MUSICA IASI water vapour profiles have been theoretically estimated considering the contribution of many different uncertainty sources. For all three climate regions, unrecognized cirrus clouds and uncertainties in atmospheric temperature have been identified as the most important error sources and they can reach about 25%.

The MUSICA IASI water vapour profiles have been compared to 100 individual coincident GRUAN water vapour profiles. The systematic difference between the data is within 11% below 12km altitude; however, at higher altitudes the MUSICA IASI data show a dry bias with respect to the GRUAN data of up to 21%. The scatter is largest close to the surface (30%), but never exceeds 21% above 1km altitude. The comparison study documents that the MUSICA IASI retrieval processor provides H2O profiles that capture the large variations in H2O volume mixing ratio profiles well from 1km above ground up to altitudes close to the tropopause. Above 5km the observed scatter with respect to GRUAN data is in reasonable agreement with the combined MUSICA IASI and GRUAN random errors. The increased scatter at lower altitudes might be explained by surface emissivity uncertainties at the summertime continental sites of Lindenberg and Sodankylä, and the upper tropospheric dry bias might suggest deficits in correctly modelling the spectroscopic line shapes of water vapour.

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In this paper MUSICA IASI tropospheric water vapour profile retrievals are evaluated by performing theoretical error assessments and comparisons to GRUAN radiosonde measurements. We show that the vertical water vapour distribution is well captured from 1 km above the ground up to the tropopause. Largest error sources are unrecognized clouds and uncertainties in atmospheric temperature, which can reach about 25 %.
In this paper MUSICA IASI tropospheric water vapour profile retrievals are evaluated by...
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