Aerosol-cloud interactions and impact on regional climate

International audienceAerosols interact with clouds through radiative and microphysical mechanisms in addition to their direct radiative effects of scattering and absorbing of solar and thermal radiation. Aerosol indirect effects consist of the modification of cloud droplet number concentrations, cloud albedo, and ice nucleating particle concentrations with ensuing effects on precipitation through aerosol perturbations. Different aerosol types present over the basin, notably dust, sea-salt and anthropogenic contribute to the formation of cloud condensation and ice nucleating particles, thus modifying cloud parameters. These processes notably occur during the frequent dust outbreaks over the Mediterranean Sea. Besides, the semi-direct aerosol effect, namely changes in cloud cover and atmospheric dynamics due to aerosol absorption, is another impact on regional climate. Regional climate simulations including aerosol-cloud interactions highlight the importance of considering aerosols, even if uncertainties are still important notably with regards to effects on cloud microphysics. To date, the direct and semi-direct effects seem to have larger impacts on the average radiative budget over the Mediterranean than the cloud-albedo indirect effect, but the question remains open concerning other indirect effects. Therefore, more observations of these interactions coupled with numerical simulations considering all these processes are needed to reduce uncertainties