An overview of the ACE-2 CLOUDYCOLUMN closure experiment

CLOUDYCOLUMN is one of the 6 ACE-2 projects which took place in June-July 1 997, between Portugal and the Canary Islands. It was specifically dedicated to the study of changes of cloud radiative properties resulting from chang es in the properties of those aerosols which act as cloud condensation nucl ei. This process is also refered to as the aerosol indirect effect on clima te. CLOUDYCOLUMN is focused on the contribution of stratocumulus clouds to that process. In addition to the basic aerosol measurements performed at th e ground stations of the ACE-2 project, 5 instrumented aircraft carried out in situ characterization of aerosol physical, chemical and nucleation prop erties and cloud dynamical and microphysical properties. Cloud radiative pr operties were also measured remotely with radiometers and a lidar. 11 case studies have been documented, from pure marine to significantly polluted ai r masses. The simultaneity of the measurements with the multi-aircraft appr oach provides a unique data set for closure experiments on the aerosol indi rect effect. In particular CLOUDYCOLUMN provided the Ist experimental evide nce of the existence of the indirect effect in boundary layer clouds formin g in polluted continental outbreacks. This paper describes the objectives o f the project, the instrumental setup and the sampling strategy. Preliminar y results published in additional papers are briefly summarized.