Periodic Reporting for period 4 - C2Phase (Closure of the Cloud Phase)
Período documentado: 2021-10-01 hasta 2023-09-30
More specifically, our objective was to test the following hypothesis: The relevant primary and secondary ice formation processes can be included in state-of-the art cloud models such that these agree in a statistical sense with space-based observations of the cloud thermodynamic phase for a wide range of conditions. The closure will be better (higher correlation between predicted and observed phase), the more physical details are included. Our research has shown that this is generally true, but that the representation of microphysical processes, in particular secondary ice formation, is still highly uncertain. Furthermore, uncertainties in the thermodynamic state of the atmosphere can introduce as large variations in the cloud phase distribution as microphysical drivers. Not all cloud-phase retrieval products for passive satellite sensors are suitable to identify fingerprints of primary and secondary ice formation.
However, in a model-to-satellite closure study for an observed case based on a day with a complex cloud scene (deep convective clouds over central Europe) using large-domain cloud resolving simulations, forward operators and the original retrieval schemes to compute artificial satellite products based on model output, these fingerprints were only conserved for rather strong microphysical perturbations and for a newly developed cloud phase retrieval scheme.
The analysis of global datasets from polar orbiting satellites has revealed large biases, but hemispheric differences and trends with cloud optical depth (defining cloud types) are consistent independent of the retrieval scheme. A set of selected global climate and storm-resolving models are generally unable to reproduce the observed characteristic cloud phase distributions for different cloud types and regions, possibly because the investigated models do not include a representation of aerosol effects on cloud droplet and ice formation. Such effects were also found in detailed studies on observed cloud phase of low- and mid-level clouds over the Arctic and Southern Oceans. Low clouds were found to exhibit less ice when over sea then over open ocean, hinting at a marine source of ice nucleating particles. Meanwhile, mid-level clouds in the same regions were found to be impacted by long-range transported mineral dust.