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Discussion papers | Copyright
https://doi.org/10.5194/acp-2018-744
© Author(s) 2018. This work is distributed under
the Creative Commons Attribution 4.0 License.

Research article 24 Jul 2018

Research article | 24 Jul 2018

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This discussion paper is a preprint. A revision of this manuscript was accepted for the journal Atmospheric Chemistry and Physics (ACP) and is expected to appear here in due course.

Intercomparison of mid-latitude tropospheric and lower stratospheric water vapor measurements and comparison to ECMWF humidity data

Stefan Kaufmann1, Christiane Voigt1,2, Romy Heller1, Tina Jurkat-Witschas1, Martina Krämer3, Christian Rolf3, Martin Zöger4, Andreas Giez4, Bernhard Buchholz5, Volker Ebert5, Troy Thornberry6,7, and Ulrich Schumann1 Stefan Kaufmann et al.
  • 1Deutsches Zentrum für Luft- und Raumfahrt, Institut für Physik der Atmosphäre, Oberpfaffenhofen, 82234, Germany
  • 2Johannes Gutenberg-Universität, Institut für Physik der Atmosphäre, Mainz, 55128, Germany
  • 3Forschungszentrum Jülich, Institute for Energy and Climate Research (IEK-7), Jülich, 52428, Germany
  • 4Deutsches Zentrum für Luft- und Raumfahrt, Flight Experiments, Oberpfaffenhofen, 822234, Germany
  • 5Physikalisch-Technische Bundesanstalt Braunschweig, Braunschweig, 38116, Germany
  • 6NOAA Earth System Research Laboratory, Chemical Sciences Division, Boulder, Colorado, USA
  • 7Cooperative Institute for Research in Environmental Sciences, University of Colorado Boulder, Boulder, Colorado, USA

Abstract. Accurate measurement of water vapor in the climate sensitive region near the tropopause turned out to be very challenging. Unexplained systematic discrepancies between measurements at low water vapor mixing ratios made by different instruments on airborne platforms have limited our ability to adequately address a number relevant scientific questions on the humidity distribution, cloud formation and climate impact in that region. Therefore, during the past decade, the scientific community has undertaken substantial efforts to understand these discrepancies and improve the quality of water vapor measurements. This study presents a comprehensive intercomparison of airborne state-of-the-art in situ hygrometers deployed onboard the DLR (German Aerospace Center) research aircraft HALO during the Mid-Latitude CIRRUS (ML-CIRRUS) campaign conducted in 2014 over central Europe. The instrument intercomparison shows that the hygrometer measurements agree within their combined accuracy (±10 to 15%, depending on the humidity regime), total mean values even agree within 2.5%. However, systematic differences on the order of 10% and up to a maximum of 15% are found for mixing ratios below 10 parts per million (ppm) H2O. A comparison of relative humidity within cirrus clouds does not indicate a systematic instrument bias in either water vapor or temperature measurements in the upper troposphere. Furthermore, in situ measurements are compared to model data from the European Centre for Medium-Range Weather Forecasts (ECMWF) which are interpolated along the ML-CIRRUS flight tracks. We find a mean agreement within ±10% throughout the troposphere and a significant wet bias in the model on the order of 100% to 150% in the stratosphere close to the tropopause. Consistent with previous studies, this analysis indicates that the model deficit is mainly caused by a blurred humidity gradient at tropopause altitudes.

Stefan Kaufmann et al.
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Interactive discussion
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Status: closed
AC: Author comment | RC: Referee comment | SC: Short comment | EC: Editor comment
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Stefan Kaufmann et al.
Stefan Kaufmann et al.
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We present an intercomparison of the airborne water vapor measurements during the ML-CIRRUS mission. Although the agreement of the hygrometers significantly improved compared to studies from recent decades, systematic differences remain under specific meteorological conditions. We compare the measurements to model data where we observe a model wet bias in the lower stratosphere close to the tropopause, likely caused by a blurred humidity gradient in the model tropopause.
We present an intercomparison of the airborne water vapor measurements during the ML-CIRRUS...
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