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Atmospheric Measurement Techniques An interactive open-access journal of the European Geosciences Union
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© Author(s) 2019. This work is distributed under
the Creative Commons Attribution 4.0 License.
© Author(s) 2019. This work is distributed under
the Creative Commons Attribution 4.0 License.

Submitted as: research article 14 Aug 2019

Submitted as: research article | 14 Aug 2019

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This discussion paper is a preprint. It is a manuscript under review for the journal Atmospheric Measurement Techniques (AMT).

Aerosol and cloud top height information of Envisat MIPAS measurements

Sabine Griessbach1, Lars Hoffmann1, Reinhold Spang2, Peggy Achtert3,a, Marc von Hobe2, Nina Mateshvili4, Rolf Müller2, Martin Riese2, Christian Rolf2, Patric Seifert5, and Jean-Paul Vernier6 Sabine Griessbach et al.
  • 1Jülich Supercomputing Centre (JSC), Forschungszentrum Jülich GmbH, Jülich, Germany
  • 2Institute of Energy and Climate Research (IEK-7), Forschungszentrum Jülich GmbH, Jülich, Germany
  • 3Department of Meteorology, Stockholm University, Stockholm, Sweden
  • 4Belgian Institute for Space Aeronomie, Brussels, Belgium & Abastumani Astrophysical Observatory, Ilia State University,Tbilisi, Georgia
  • 5Leibniz Institute for Tropospheric Research (TROPOS), Leipzig, Germany
  • 6NASA Langley Research Center, Hampton, VA, USA
  • anow at: Department of Meteorology, University of Reading, Reading, UK

Abstract. Infrared limb emission instruments have a long history in measuring clouds and aerosol. In particular the Michelson Interferometer for Passive Atmospheric Sounding (MIPAS) instrument aboard ESA's Envisat provides 10 years of altitude resolved global measurements. Previous studies found systematic over- and underestimations of cloud top heights for cirrus and polar stratospheric clouds. To assess the cloud top height information and to characterize its uncertainty for the MIPAS instrument we performed simulations for ice clouds, volcanic ash, and sulfate aerosol. From the simulation results we found that in addition to the known effects of the field-of-view that can lead to a cloud top height overestimation, and broken cloud conditions that can lead to underestimation, also the cloud extinction plays an important role. While for optically thick clouds the possible cloud top height overestimation for MIPAS reaches up to 1.6 km due to the field-of-view, for optically thin clouds and aerosol the systematic underestimation reaches 5.1 km. For the detection sensitivity and the degree of underestimation of the MIPAS measurements also the cloud layer thickness plays a role. 1 km thick clouds are detectable down to extinctions of 5 x 10-4 km-1 and 6 km thick clouds are detectable down to extinctions of 1 x 10-4 km-1, where the largest underestimations of the cloud top height occur for the optically thinnest clouds with a vertical extent of 6 km. The relation between extinction coefficient, cloud top height estimate, and layer thickness is confirmed by a comparison of MIPAS cloud top heights of the volcanic sulfate aerosol from the Nabro eruption in 2011 with space- and ground-based lidar measurements and twilight measurements between June 2011 and February 2012. In the fresh to two months old plume, where the extinction was between 1 x 10-4 and 7 x 10-4 km-1 and the layer thickness mostly below 4 km, we found for MIPAS an average underestimation of 1.1 km. In the aged plume with extinctions down to 5 x 10-5 km-1 and layer thicknesses of up to 9.5 km the underestimation was higher reaching 7.2 km. The dependency of the cloud top height over- or underestimation on the extinction coefficient can explain seemingly contradictory results of previous studies. In spite of the relatively large uncertainty range of the cloud top height, the comparison of the detection sensitivity towards sulfate aerosol between MIPAS and a suite of widely used UV/VIS limb and IR nadir satellite aerosol measurements shows that MIPAS provides complementary information in terms of detection sensitivity.

Sabine Griessbach et al.
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Sabine Griessbach et al.
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Short summary
In this paper we study the cloud top height derived from MIPAS measurements. Previous studies showed contradictory results with respect to MIPAS both under- and overestimating cloud top height. We used simulations and found that over- and/or underestimation depend on cloud extinction. To support our findings we compared MIPAS cloud top heights of volcanic sulfate aerosol with measurements from CALIOP, ground based lidar and ground based twilight measurements.
In this paper we study the cloud top height derived from MIPAS measurements. Previous studies...