| Popis: |
The cloud droplet number concentration (CDNC) is one of the most important microphysical properties of liquid clouds for understanding and quantifying the effective radiative forcing by aerosol-cloud interactions (ERFaci). Indeed, CDNC is directly linked to the relevant processes of the cloud formation and evolution and is closely related to the chemical composition of the cloud condensation nuclei and the cloud droplet size distribution. Nevertheless, this key parameter still remains poorly known and is not yet operationally provided from current standard satellite retrievals. Our approach relies on an innovative determination of CDNC from satellite observations in combination with atmospheric modelling across scales, i.e., from cloud-resolving to global climate modelling. We introduce our new, community-based tool: the Satellite Simulator and Sandbox for Cloud Observation and Modelling (S3COM). Briefly, S3COM aims to simulate realistic satellite observations and cloud products from model outputs, to quantify the sensitivity of radiative quantities to cloud parameters, and to assist the development of retrieval algorithms using output fields from high-resolution models. We use realistic cloud situations (stratocumulus, cumulus, marine and continental clouds) obtained from the ICOsahedral Nonhydrostatic Large Eddy Model (ICON-LEM) to simulate top of atmosphere radiances with the Radiative Transfer for TOVS (RTTOV), from visible to infrared, observed by the Moderate Resolution Imaging Spectroradiometer (MODIS). Performance of MODIS-type algorithms coupled with ICON-LEM simulations is described and characterization of error sources is given. First results on the CDNC retrievals for warm liquid water stratocumulus clouds are presented and discussed. To go further in the improvements of the CDNC retrievals, the potentials of the multi-angle polarization and multi-viewing angle approaches using the POLarization and Directionality of the Earth's Reflectances (POLDER) observations will be investigated in a next step. |
