Chemistry, cloud and radiation interactions in a meteorological model

Principal Investigator

Prof G Cautenet
L.A.M.P.
24 Av de Landais
63170 Aubiere Cedex
France

cautenet@opgc.univ-bpclermont.fr

Project description

Study of photochemistry, vertical transport of chemical species by cloud scavenging and wet deposition in the framework of a 3D mesoscale meteorological model including detailed microphysics, based upon MLOPEX (1991-92, Hawaii) and DECAFE (since 1987, Congo).

Since the beginning, this project has developed many sides, all of them centred on the core theme of the mesoscale atmospheric physico-chemistry and radiation: photochemistry, aqueous and gaseous chemistry, transport of gas and aerosols species, radiation, clouds/chemistry/radiation interactions. These are the main axes of our laboratory, and at least 3 staffs are involved in it. Our scientific goals are: interpretation of observations, tests of hypotheses and build-up of parameterisations suitable for large scale models. Our tools are: a mesoscale model (RAMS, Colorado University) and cloud-scale model (Clark), coupled with special modules (transport, deposition, chemistry, radiation). We can develop as follows the main sides of this project:

• Dynamical and chemical redistribution of pollutants from surface emissions over large areas. Our investigations focus on large experiments such as EXPRESSO in Central Africa and INDOEX over Indian Ocean, or the future AMMA/WAM experiments over West Africa. Even though WAM means "West African Monsoon", a complete year will be investigated, including not only the deep convection and squall lines phenomena of the wet season (which involves severe desert dust uptakes), but the dry season features too, including the biomass burning emissions. The last aspect will help us to continue the study of aqueous chemistry in the tropical regions.
• Dynamical and chemical redistribution of pollutants over smaller areas: urban pollution experiments over complex terrain, such as the ESCOMPTE experiment (Marseilles).
• Study of the condensation processes, and associated rainfalls. The numerical model is the Clark model, and some recent observations as regards nucleation processes (from microphysics experiments at the Puy de Dome station, such as CIME experiment) are included in its detailed microphysics module. This model is also used in view to explain some severe rain events in Southern France.
• Interpretation of ozone observations at the Puy de Dome station: before modelling it, we need to analyse the possible origin of the pollutants, using (back)trajectories. Our aim is to better understand the ozone signal in view to include this station in an European network.
• Direct, semidirect and indirect effects of aerosols. Our observations over Atlantic (Tropical Eastern side) suggest that some interaction may occur between desert dust plumes and the stratiform cloud cover (indirect effect). We therefore develop the modelling of the atmospheric cycle of these particles, including the possible interaction with the liquid water phase (clouds). We model this cycle in various areas: Africa, Indian Ocean (Arabia dust sources), China in the framework of Ace-Asia experiment. In the same way, the other main aerosols (carbonaceous, non sea-salt sulphate, sea salts) are modelled too, and possible mixing of all these particles is considered. Here we focus on the semidirect possible effect: the large, optically absorbing aerosol plumes are likely to strongly control the solar heating of the column and consequently impact on the clouds development (at least the stratiform clouds, which are very important for the radiative budget).

All these tasks need the ECMWF analysis data, for trajectories, and models initialisation and nudging. Observation data are used in some instances (an example is: visibility over deserts, in view to detect dust uptakes, which is not easy with satellite data).

For more details, please also refer to the latest progress report.

Additional information

Project period 1993-2004.