Large-eddy simulations analyzing the impact of RV Polarstern on surrounding measurements during MOSAiC

The Arctic atmospheric boundary layer (ABL) is a driver of current and future Arctic warming. Yet, the Arctic ABL provides many distinct and nearly idealized cases for investigation. The contrast between polar day and night and the lack of a diurnal cycle and complex topography promotes the formation and observation of persistent ABL states that are usually only short-term in lower latitudes. In 2019 and 2020, the yearlong MOSAiC expedition [1] took place to inject our understanding of the reasons and consequences of current rapid Arctic warming. Its tailor-made combination of atmospheric measurements gathered by the research vessel Polarstern, aircraft, drones, radiosondes, balloons, and various surface-based and remote sensing systems provides us with vast data to analyze.

To ensure MOSAiC data quality and support future data analysis, we apply large-eddy simulations (LESs) for selected weather conditions during MOSAiC, using the PALM model [2] and resolutions of up to less than a meter. Such fine grid spacings allow us to resolve the ship's envelope as an obstacle to the flow and sufficiently represent stably stratified ABLs. PALM's virtual measurement module enables our LESs to create synthetic perturbed and unperturbed observational data. Thus, analysis of their difference and the ship-induced wakes provides an insight into the ship's effects on surrounding in-situ measurements, which is a central aspect for interpreting corresponding data.

Our simulations reveal that effects are not only tied directly to the ship's wake within the turbulent flow. They indicate that ship-induced gravity waves also bear the potential to influence surrounding measurements notably (i. e. their accuracy exceeding). We present and analyze:

• how influences from both sources rely on atmospheric conditions, the measurement positioning, and the considered atmospheric quantity
• that effects notably perturb performed measurements frequently up to more than a kilometer distance
• the underlying mechanisms causing the observed perturbations
• mitigation and interpretation strategies to work with corresponding data

[1] Shupe, M. D. et al. (2022): Overview of the MOSAiC expedition: Atmosphere. Elementa: Science of the Anthropocene. DOI: 10.1525/elementa.2021.00060.
[2] Maronga, B., et al. (2020): Overview of the PALM model system 6.0, Geoscientific Model Development. DOI: 10.5194/gmd-13-1335-2020.