Evaluation of operational model forecasts of aerosol transport usingceilometer network measurements

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 0.2 km (typical overlap range of ceilometers) and 1 km, 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.