1) Aerosol Conditions
A detailed analysis of aerosol properties from space or with passive sensors is hardly achievable. Using lidar techniques as the central component for our aerosol studies will provide insights into macrophysical and microphysical aerosol properties, ranging from the vertical layering of aerosols up to retrievals of profiles of aerosol particle number size distributions.
2) Mixed-phase clouds and precipitation
What is the phase portioning in mixed-phase cloud layers? How are the properties of mixed-phase clouds and precipitation related to variations in aerosol conditions and atmospheric dynamics? Will it be possible to distinguish primary ice formation processes from secondary ice formation? Can we clearly identify regionally varying cloud and precipitation properties that can be attributed to aerosol variability? Which measurement accuracy is required to disentangle thermodynamic from aerosol-related effects on clouds and precipitation?
3) Certain aerosol types as reservoir for cloud condensation nuclei and ice-nucleating particles
Laboratory studies show that the ability to form ice heterogeneously at temperatures between 0 and -40°C depends strongly on the type of aerosol particles involved in the cloud process. By conducting campaigns in the frame of DACAPO in regions of strongly varying aerosol conditions we will obtain observational datasets that can be used to evaluate the laboratory studies. In addition, the observations will allow to develop novel parameterizations for relating lidar-observed aerosol optical properties to the availability of nuclei for cloud condensation and ice crystals.
4) Radiative Closure
Radiative properties of clouds vary strongly with their microphysical and macrophysical structure. Is a radiation closure possible using the measured cloud and aerosol properties together with their radiative properties? Are there any biases left, which are not covered by our measurements? If yes, how can these differences be explained?
Numerical weather prediction models currently assume constant aerosol conditions or even the absence of any aerosol effects on modeled cloud and precipitation properties. Do these assumptions, i.e., parameterizations, hold for all regions around the globe? Or can we identify the need for considering aerosol properties in parameterizations of cloud and precipitation processes?
Also, linking highly resolved measurements of cloud and aerosol properties, precipitation and dynamics requires novel modeling approaches that also take the size and number of involved particles into account. Forward operators are needed to translate modeled microphysical parameters to measurements. The current number and capabilities of such forward operators are limited and motivates additional development efforts.
6) Overarching objectives
Observations at key places of aerosol conditions around the globe as done in the frame of DACAPO are valuable not only for the scientific goals listed above. The datasets will also be used for the evaluation of satellite retrievals and to support new satellite missions in their starting phase. Such actions are already scheduled for the upcoming ESA missions ADM Aeolus and EarthCARE.
The availability of the long-term observations at remote station will also be used to identify and characterize the individual meteorological complexity of the different sites. Such information will be helpful for both, planning of future measurement missions, and for local authorities.