Analysis of Arctic Stable Boundary Layers During the ISOBAR Field Campaign

The Innovative Strategies for Observations in the Arctic Atmospheric Boundary Layer (ISOBAR) field campaigns took place in February 2017 and 2018 on the island of Hailuoto, Finland. This location was chosen specifically for its seasonal sea ice along the coast, allowing for Arctic stable boundary layers to evolve in the evenings. An innovative combination of remotely piloted aircraft systems (RPAS), surface eddy covariance towers, sodars, and a Doppler wind lidar was leveraged to improve the conceptual understanding of stable boundary layers (SBL) over sea ice in the Bothnian Bay. Traditionally, numerical weather prediction models underperform in regimes of strongly stable stratification, and conventional observations are restricted to the lowest 10 meters above ground level. This campaign aimed to bridge this data gap by regularly flying RPAS vertical profiles throughout the night to capture the thermodynamic and kinematic structure of the ABL and the free atmosphere aloft at high spatiotemporal resolution in order to study different boundary layer phenomena under stably stratified conditions and their interactions with the surface fluxes. Rotary-wing RPAS would fly vertical profiles from the surface to 300 m in roughly 20 minute intervals throughout the night, collecting pressure, temperature, and humidity measurements and estimating horizontal wind speeds based on their tilt angles. To fill in a deeper portion of the free atmosphere, fixed-wing RPAS would fly helical ascents from the surface to 1800 m every hour throughout the night, also collecting pressure, temperature, and humidity data and directly measuring the 3-dimensional wind field using a pitot tube.

To create a composite dataset spanning across multiple aircraft with different sampling capabilities, it is necessary to correct to a common reference measurement. The 10 m tower was chosen for this purpose. Additionally, the RPAS measurements must be corrected for response time and altitude estimation. By synthesizing flights from both fixed- and rotary-wing RPAS in time-height coordinates, inherent biases at different levels can also be accounted for to obtain an unprecedented view of the SBL. Using this dataset, this presentation will focus on the structure of the SBL during different intermittent cases and how generation of turbulence is related to Richardson number profiles.