We propose to use the suite of instruments on NASA�s Aqua satellite to globally study the microphysics of stratiform boundary layer clouds and its relation to cloud albedo. Based on the preliminary work that was performed in preparation for this proposal, we believe that a chief outcome of this project could be a significant reduction in the uncertainty of the magnitude of the first indirect aerosol effect globally based on observations.
One key component of the proposed study is that it will make use of an innovative technique that allows to remotely sense cloud droplet number concentration and an effective geometrical thickness. This technique allows to discriminate cloud microphysical effects from cloud dynamics better than traditional approaches and is thus excellently suited to address the issue of pollution and its impact on cloud albedo. In particular, the following three issues will be addressed and are discussed in more detail in the full proposal:
- The combination of MODIS, AMSR-E, and CERES on Aqua will allow to experimentally quantify the variability of cloud droplet number concentration and cloud geometrical thickness as well as their impact on shortwave albedo. Cloud droplet number concentration is of high scientific relevance by itself, but it will also establish a global reference dataset for validation of global climate models (GCMs).
- Regional studies of variability of cloud droplet number concentration will be performed. These studies will allow to study the impact of e.g. biomass burning events on cloud albedo. Those studies will make use of auxiliary information such as backwards trajectories to link changes in cloud microphysics to regional sources.
- An attempt will be made to attribute changes in cloud droplet number concentration to anthropogenic sources based on aerosol observations. Each step will be accompanied by an extensive error analysis of all components within the process leading to realistic error estimates for all derived parameters.
