Impact of aerosol on post-frontal convective clouds over Germany

Abstract

We carried out simulations with predefined and simulated aerosol distributions in order to investigate the improvement in the forecasting capabilities of an operational weather forecast model by the use of an improved aerosol representation. This study focuses on convective cumulus clouds developing after the passage of a cold front on 25 April 2008 over Germany. The northerly flow after the cold front leads to increased sea salt aerosol concentrations compared to prefrontal conditions. High aerosol number concentrations are simulated in the interactive scenario representing typically polluted conditions. Nevertheless, due to the presence of sea salt particles, effective radii of cloud droplets reach values typical of pristine clouds (between 7 µm and 13 µm) at the same time. Compared to the predefined continental and maritime aerosol scenarios, the simulated aerosol distribution leads to a significant change in cloud properties such as cloud droplet radii and number concentrations. Averaged over the domain covered by the convective cumuli clouds, we found a systematic decrease in precipitation with increasing aerosol number concentrations. Differences in cloud cover, short wave radiation and cloud top heights are buffered by systematic differences in precipitation and the related diabatic effects. Comparisons with measured precipitation show good agreement for the interactive aerosol scenario as well as for the extreme maritime aerosol scenario.

• aerosol–cloud interaction
• precipitation
• natural aerosol
• anthropogenic aerosol
• regional modelling

6. Acknowledgements

The authors wish to thank the following persons for their contributions to this study: Axel Seifert (DWD) for pointing out this period for further research with COSMO-ART and also for supporting us with measurements and advices. Jochen Förstner (DWD) for providing us with operational initial and boundary conditions. Andrew Ferrone (CRPGL) for preprocessing the AIRBASE data. Christoph Knote (EMPA, NCAR) for preparing the anthropogenic emission data.

The authors acknowledge the use of Rapid Response imagery from the Land Atmosphere Near-real time Capability for EOS (LANCE) system operated by the NASA/GSFC/Earth Science Data and Information System (ESDIS) with funding provided by NASA/HQ.

Finally, the authors thank our reviewers for their useful, comprehensive and very constructive comments.