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3rd HyMeX workshop 1-4 June 2009 Heraklion (Gournes), Crete-Greece

Aerosol-cloud-precipitation-radiadion feedbacs and their impacts on water budget

George Kallos (National and Kapodistrian University of Athens (NKUA)); S. Solomos, C. Spyrou, C. Mitsakou, J. Kushta, E. Tyrlis

The Mediterranean region is characterized by its unique climatic conditions and the associated physic-chemical processes. More specifically, the mixture of different age of air pollutants of anthropogenic origin with Saharan dust and sea salt may lead to the formation of other particles with different characteristics. The mixture of the aerosols and gases from anthropogenic and natural origin (desert dust and sea salt) results in the formation of new types of PM with different physico-chemical properties and especially hygroscopicity (e.g. inside clouds or within the marine boundary layer) through heterogeneous processes. The new particle formation has different characteristics and therefore they have different impacts on cloud formation and precipitation.

Modeling the dust cycle in the atmosphere at the University of Athens started in the mid-nineties with the development of the SKIRON/Dust atmospheric modeling system. The dust cycle module is directly coupled with the meteorological model and in its early development was called DREAM. Recent model development includes log-normal particle size distribution (eight bins), calculation of Aerosol Optical Depth (AOD), radiative transfer corrections by utilizing look up tables (shading effect), new dust source identification and utilization of rocky soil characterization, replacement of the dry and wet deposition schemes with more accurate ones, in-cloud scavenging, etc. The old radiative transfer scheme from GFDL has been replaced by the Rapid Radiative Transfer Model - RRTM for both short and long wave radiation. The new radiative transfer scheme has many properties that allow the description of dust impacts in the atmosphere on a more accurate way. Mid and low tropospheric warming by dust is one of the new features that the model can describe. Some of these properties will be discussed during the presentation.

In an attempt to better understand links and feedbacks between air pollution and climate the new Integrated Community Limited Area Modeling System ¿ ICLAMS has been developed. ICLAMS is an enhanced version of RAMS.6 modeling system. It includes sub-models for the dust and sea salt cycles, gas and aqueous phase chemistry, gas to particle conversion and heterogeneous chemistry processes. All these processes are directly coupled with meteorology. RAMS has an explicit cloud microphysical scheme with eight categories of hydrometeors. The photochemical processes are directly linked to the RAMS radiative transfer scheme. The system is capable to be configured on two-way interactive nesting with any number of nested grids with resolution ranging from tens of kilometers to a few tens of meters. ICLAMS has the capability to treat CCN, GCCN and IN as predictive quantities.

Potential contribution to HYMAX: Study in depth the aerosol-cloud-precipitation-radiation interactions and their impact on water cycle. More specifically it is planned to study the impact of dust, sea salt on clouds and precipitation under certain conditions ranging from regular events to outbreaks of severe phenomena. In general, it is known that aerosols and desert dust supress precipitation. Although this is not always the case as it will be discussed. The composition of the aerosols in the atmosphere along the long paths, the composition changes and therefore the impacts on clouds will be examined. In this workshop the basic structure, the new model development capabilities will be presented and some results will be discussed.