CLACE GAW Plus

Duration: 2000-

Contact: Martin Gysel, martin.gysel@psi.ch

Aerosols influence the atmospheric energy budget through direct and indirect effects:

• Direct radiative effects include the scattering and absorption of solar radiation and the subsequent influence on planetary albedo and the climate system.
• Indirect effects involve the influence of the aerosol on cloud properties, cloud lifetime and cloud cover through acting as cloud condensation nuclei (CCN) and ice nuclei (IN). Anthropogenic changes of the atmospheric aerosol loadings are expected to cause an overall negative climate forcing partially offsetting the positive forcing by greenhouse gases.

However, the aerosol effects are still poorly quantified due to the inhomogeneity of global aerosol loadings and chemical composition as well as the complexity of involved interactions and feedbacks. A major gap in the quantification of the aerosol indirect effect is the poor quantification of the global distribution of CCN.

Currently, we investigate microphysical properties of the prevailing liquid clouds at the Jungfraujoch station. Here we compare in situ measured ambient cloud droplet number concentrations with CCN number concentrations that were derived from laboratory measurements. These measurements will allow for the determination of the effective peak supersaturation in the prevailing ambient cloud which was responsible for the activation of aerosol particles to cloud droplets. These measurements represented an important part of a quality assurance procedure because the cloud droplet sampling process is critical and might bias the results derived from the laboratory based measurements. We seek for collaborations with the cloud modeling community because we believe that our observations have the potential to be successfully implemented in various models, contributing to a better quantification of the indirect aerosol effect on climate.

Starting in 2000, these CLACE (cloud and aerosol characterization experiment) campaigns take place in regular intervals. These comprehensive aerosol - cloud interaction studies are conducted within national and international collaborations.

See list of CLACE related publications