Aerosol-Cloud-rADiation-Interaction over Aotearoa (ACADIA)

• Applicants: Professorin Dr. Heike Kalesse-Los; Dr. Patric Seifert
• Subject Area: Atmospheric Science
• Term: since 2025
• Project identifier: Deutsche Forschungsgemeinschaft (DFG) - Project number 558943790

In recent decades, considerable progress has been made in the ascertainment of the role of aerosol particles in cloud processes. It is unquestionable that down to temperatures of -38°C each primarily formed liquid or frozen hydrometeor requires an aerosol particle for its formation which acts either as cloud condensation nuclei (CCN) or ice nucleating particle (INP). A quantification of the influence which perturbations in the aerosol load do have on a clouds’ microphysical structure and its evolution is nevertheless still hardly achievable. There is a strong need to improve this lack of scientific understanding, because state-of-the-art physical representations of cloud processes show a lack of accuracy especially in regions where the aerosol load deviates from the general mean. A key region on Earth where this issue becomes most obvious is the area of the Southern Ocean in the mid-latitudes of the Southern Hemisphere. On the one hand, this region is amongst those with the lowest aerosol loads on the globe. On the other hand, the abundance of supercooled liquid water at temperatures between 0 and -38°C over this region is amongst the highest that can be observed. Even state-of-the-art general circulation models (GCM) either cannot reproduce this prominent feature or shift the biases to other parameters. This suggests that the current scientific understanding of the relationship between aerosol perturbations and cloud microphysical properties has considerable deficiencies. Consequences are strong biases between the simulated and observed radiation budget and an inaccurate representation of precipitation patterns in the simulations. It is scope of this project proposal to conduct a unique, focused, well-positioned contrast study which is about to disentangle the relationships between aerosol load, cloud and precipitation processes, and the radiation budget, based on a 1-year multi-site field campaign on the South Island of Aotearoa New Zealand. We will exploit the alternation of Australian and Southern-Ocean dominated air masses and the transformation processes during transport over 400 km of landmass of the South Island between two atmospheric remote-sensing sites (Invercargill, Tāwhaki) to disentangle the role of aerosol load on the microphysical and radiative properties of clouds and their evolution. While the proposed project stands alone and independent, it will be embedded in a series of already scheduled field experiments, including the deployment of the HALO aircraft, the research vessel Sonne, and the mobile ground-based remote sensing infrastructure LACROS from TROPOS.

• DFG Programme: Research Grants