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Discussion papers | Copyright
https://doi.org/10.5194/gmd-2018-74
© Author(s) 2018. This work is distributed under
the Creative Commons Attribution 4.0 License.

Model evaluation paper 02 May 2018

Model evaluation paper | 02 May 2018

Review status
This discussion paper is a preprint. A revision of this manuscript was accepted for the journal Geoscientific Model Development (GMD) and is expected to appear here in due course.

Evaluation of operational model forecasts of aerosol transport using ceilometer network measurements

Ka Lok Chan1,2, Matthias Wiegner1, Harald Flentje3, Ina Mattis3, Frank Wagner3,4, Josef Gasteiger5, and Alexander Geiß6 Ka Lok Chan et al.
  • 1Meteorological Institute, Ludwig-Maximilians-Universität München, München, Germany
  • 2Remote Sensing Technology Institute, German Aerospace Center (DLR), Oberpfaffenhofen, Germany
  • 3Department of Research and Development, Meteorological Observatory Hohenpeißenberg, German Weather Service (DWD), Hohenpeißenberg, Germany
  • 4Institute for Meteorology and Climate Research, Karlsruhe Institute of Technology, Eggenstein-Leopoldshafen, Germany
  • 5Aerosol Physics and Environmental Physics, University of Vienna, Austria
  • 6European Space Research and Technology Centre, European Space Agency, Netherlands

Abstract. In this paper, we present a comparison of European Centre for Medium-Range Weather Forecast Integrated Forecast System (ECMWF-IFS) model simulation of aerosol backscatter profiles with measurements of the ceilometer network operated by the German weather service (DWD) over 1 year from September 2015 to August 2016. As the model output provides mass mixing ratios of different types of aerosol whereas the ceilometers don't, it is necessary to determine a common physical quantity for the comparison. We have chosen the attenuated backscatter β* for this purpose. The β*-profiles are calculated from the mass mixing ratios of the model output assuming the inherent aerosol microphysical properties. Comparison of the attenuated backscatter, averaged between an altitude from 0.2km (typical overlap range of ceilometers) and 1km, showed slightly larger values from the model.

To investigate possible reasons for the differences, we have examined the role of the hygroscopic growth of particles and the particle shape. Our results show that using a more recent particle growth model would result in a ~22% reduction of particle backscatter for sea salt aerosols, corresponding to a 10%-reduction of the total backscatter signal on average. Accounting for non-spherical dust particles in the model would reduce attenuated backscatter of dust particles by ~30%. As the concentration of dust aerosol is in general very low in Germany, a significant effect on the total backscatter signal is restricted to dust episodes. In summary, consideration of both effects tend to improve the agreement between model and observations, but without leading to a perfect consistency.

In addition a case study was conducted to investigate the agreement of the spatiotemporal distribution of particles. It was found that for a dust episode in April 2016 the arrival time of the dust layer and its vertical extent very well agree between model and ceilometer measurements for several stations. However, due to the large set of parameters characterizing the aerosol distribution and the complexity of the ceilometer retrieval an automated and quantitative comparison scheme for β*-profiles is still missing. Consequently, the representativeness of the case study remains open.

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Ka Lok Chan et al.
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Ka Lok Chan et al.
Ka Lok Chan et al.
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The manuscript presents the comparison of ECMWF-IFS model simulation of aerosol backscatter profiles to long-term measurements of an extended ceilometer network. A significant influence of the numerical description of the hygroscopic growth of sea salt aerosols on the agreement between model and observations was found. Consideration of the non-sphericity of dust particles in the model reduces the attenuated backscatter of dust by ~ 30 % and improved the agreement between model and observations.
The manuscript presents the comparison of ECMWF-IFS model simulation of aerosol backscatter...
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