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Volume 11, issue 9 | Copyright
Geosci. Model Dev., 11, 3807-3831, 2018
© Author(s) 2018. This work is distributed under
the Creative Commons Attribution 4.0 License.

Model evaluation paper 25 Sep 2018

Model evaluation paper | 25 Sep 2018

Evaluation of ECMWF-IFS (version 41R1) operational model forecasts of aerosol transport by using ceilometer network measurements

Ka Lok Chan1,2, Matthias Wiegner1, Harald Flentje3, Ina Mattis3, Frank Wagner3,a, Josef Gasteiger4, and Alexander Geiß1 Ka Lok Chan et al.
  • 1Meteorological Institute, Ludwig-Maximilians-Universität München, Munich, 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
  • 4Aerosol Physics and Environmental Physics, University of Vienna, Vienna, Austria
  • anow at: Institute for Meteorology and Climate Research, Karlsruhe Institute of Technology, Eggenstein-Leopoldshafen, Germany

Abstract. In this paper, we present a comparison of model simulations of aerosol profiles with measurements of the ceilometer network operated by the German Weather Service (DWD) over 1 year from September 2015 to August 2016. The aerosol forecasts are produced by the Copernicus Atmosphere Monitoring Service (CAMS) using the aerosol module developed within the Global and regional Earth-system Monitoring using Satellite and in-situ data (GEMS) and Monitoring Atmospheric Composition and Climate (MACC) projects and coupled into the European Centre for Medium-Range Weather Forecasts Integrated Forecasting System (ECMWF-IFS). As the model output provides mass mixing ratios of different types of aerosol, whereas the ceilometers do not, 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 of 0.2km (typical overlap range of ceilometers) and 1km in general shows similar annual average values. However, the standard deviation of the difference between model and observation is larger than the average in 8 out of 12 sites.

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 nonspherical 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 tends to improve the agreement between model and observations but without leading to a perfect consistency.

In addition, a strong Saharan dust event was investigated to study the agreement of the spatiotemporal distribution of particles. It was found that the arrival time of the dust layer and its vertical extent very well agree between model and ceilometer measurements for several stations. This underlines the potential of a network of ceilometers to validate the dispersion of aerosol layers.

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Short summary
The paper 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 nonsphericity of dust particles in the model reduced the attenuated backscatter of dust by ~&thinp;30 % and improved the agreement between model and observations.
The paper presents the comparison of ECMWF-IFS model simulation of aerosol backscatter profiles...