Large-eddy simulations of the polar boundary layer during the ISOBAR measurement campaigns and test of the gradient-based similarity concept under stable conditions

This project aims at investigating the polar boundary layer as it was observed in two intensive field campaigns at Hailuoto, Finland (ISOBAR campaign), during February 2017 and 2018.
In the ISOBAR campaign, ground-based flux and profile observations are combined with boundary layer remote sensing methods and the extensive usage of different unmanned aircraft systems (UAS). The campaigns extensively probed numerous stable and very stable boundary layer cases, characterized by strong stratification, weak winds, and clear skies. Rapid changes in the vertical boundary layer structure were observed, potentially related to shear instabilities of a low-level jet, rapid strong cooling events a few meters above ground, and wave-breaking events triggering intensive turbulence near the surface.
The underlying processes are not understood so far. Moreover, first attempts are currently made to test the gradient-based similarity theory under stable conditions based on ISOBAR data. The performance in large-eddy simulation (LES) models to simulate very stable conditions has not been tested and evaluated against in-situ data.

The goal of the project is to use the LES model PALM to simulate selected boundary layers as observed during ISOBAR in search for physical explanations for the observed boundary layer features described above. Furthermore, the gradient-based similarity relationships shall be calculated based on LES data and compared against those from ISOBAR data. Finally, the gradient-based similarity relationships shall be implemented in PALM as a surface boundary condition in search for a more reliable performance when simulating very stable conditions.

This work will be conducted in close collaboration with Prof. Joachim Reuder and his research group at the Geophysical Institute at the University of Bergen.