Project Summary

Recent studies of cloud interactions with particulate air pollution, performed mostly on a conceptual level, show that pollution aerosols can invigorate convection into severe storms. Convective storms are defined as severe when they produce at least one of the following phenomena: strong local winds, downbursts, frequent lightning, large hail and tornados. The pollution aerosols can slow the conversion of cloud drops into precipitation, allowing the convective energy to accumulate and eventually trigger violent storms.
The new METEOSAT Second Generation (MSG) geostationary satellite, commissioned in January 2004 by the European Organization for the Exploitation of Meteorological Satellites (EUMETSAT), can significantly help identifying in real time the impacts of pollution aerosols on cloud structure, and thus potentially provide advanced warning of such events. Satellite and ground based observations in conjunction with computer models are used to distinguish the meteorological and pollution aerosols effects on triggering and invigorating severe convective storms, and hence causing man-made "natural disasters”.
In addition to fundamental understanding of the anthropogenic role in influencing severe storms, the project will provide the scientific basis to improve the skill of numerical weather prediction (NWP) models to predict such storms. The ultimate challenge may be to develop a method by which severe storm development can be mitigated, for example by reducing aerosol pollution, or even reverse the effect of the small pollution aerosols by introducing large hygroscopic aerosols that accelerate the early onset of rain. The scientific basis of such a possibility will be evaluated.

Relevant publications
Titel	Quelle	Kurzbeschreibung
A comparison of spectral bin and two-moment bulk mixed-phase cloud microphysics	Atmos.Res., 80, 46-66, DOI 10.1016/j.atmosres.2005.06.009 (2006)
A two-moment cloud microphysics parameterization for mixed-phase clouds. Part I: Model description	Meteorol. Atmos. Phys.,92, 45-66, DOI10.1007/s00703-005-0112-4, (2006)	A two-moment microphysical parameterization for mixedphase clouds was developed to improve the explicit representation of clouds and precipitation in mesoscale atmospheric models. The scheme predicts the evolution of mass as well as number densities of the five hydrometeor types cloud droplets, raindrops, cloud ice, snow and graupel. Since the number concentrations of all these hydrometeors are calculated explicitly, all relevant homogenous and heterogenous nucleation processes have been parameterized including the activation of cloud condensation nuclei, which is not predicted in most state-of-the-art cloud resolving models. Therefore the new scheme can discriminate between continental and maritime conditions and can be used for investigations of aerosol effects on the precipitation formation in mixed-phase clouds. In addition, the scheme includes turbulence effects on droplet coalescence, collisional breakup of raindrops and size-dependent collision efficiencies. A new general approximation of the collection kernels and the corresponding collision integrals is introduced.
A two-moment cloud microphysics parameterization for mixed-phase clouds. Part II: Deep convective storms	Meteorol. Atmos. Phys., 92, 67-82, DOI 10.1007/s00703-005-0113-3 (2006)	A systematic modeling study investigates the effects of cloud condensation nuclei (CCNs) on the evolution of mixedphase deep convective storms. Following previous studies the environmental conditions like buoyancy and vertical wind shear are varied to simulate different storm types like ordinary single cells, multicells and supercells. In addition, the CCN characteristics are changed from maritime to continental conditions. The results reveal very different effects of continentality on the cloud microphysics and dynamics of the different storms. While a negative feedback on total precipitation and maximum updraft velocity is found for ordinary single cells and supercell storms, a positive feedback exists for multicell cloud systems. The most important link between CCN properties, microphysics and dynamics is the release of latent heat of freezing.

Rosenfeld D., 2000: Suppression of Rain and Snow by Urban and Industrial Air Pollution. Science, 287 (5459), 1793-1796.
Andreae M. O., D. Rosenfeld, P. Artaxo, A. A. Costa, G. P. Frank, K. M. Longo, and M. A. F. Silva Dias, 2004: Smoking rain clouds over the Amazon. Science, 303, 1337-1342.

Khain, A. P., A. Pokrovsky, and I. L. Sednev, 1999: Some effects of cloud-aerosol interaction on cloud microphysics structure and precipitation formation: numerical experiments with a spectral microphysics cloud ensemble model. Atmos. Res., 52, 195-220.

Lelieveld, J., J. H. Berresheim, S. Borrmann, P.J. Crutzen, F.J. Dentener, H. Fischer, J. Feichter, P.J. Flatau, J. Heland, R. Holzinger, R. Korrmann, M.G. Lawrence, Z. Levin, K.M. Markowicz, N. Mihalopoulos, A. Minikin, V. Ramanathan, M. de Reus, G.J. Roelofs, H.A. Scheeren, J. Sciare, H. Schlager, M. Schultz, P. Siegmund, B. Steil, E.G. Stephanou, P. Stier, M. Traub, C. Warneke, J. Williams, H. Ziereis, 2002: Global air pollution crossroads over the Mediterranean, Science, 298, 794 - 799.

Setvák, M., R. M. Rabin, C. A. Doswel III, and V. Levizzani, 2003: Satellite observations of convective storm top features in the 1.6 and 3.7/3.9 µm spectral bands. Atmos. Res., 67-68, 607-627.

Consortium

Profs Daniel Rosenfeld (coordinator), Alexander Khain
Institute of Earth Sciences
Hebrew University Jerusalem, Israel

Profs Jos Lelieveld, Meinrat Andreae,
Max-Planck Institute for Chemistry, Mainz, Germany

Prof Klaus D. Beheng,
Institute for Meteorology and Climate Research,
University Karlsruhe/Research Centre Karlsruhe, Germany

Drs Vincenzo Levizzani, Elsa Cattani
Istituto di Scienze dell’Atmosfera e del Clima
Consiglio Nazionale delle Ricerche (CNR), Bologna, Italy

This project is funded by EC as STREP project as part of FP6-2003-NEST-B1.