Abstract
The aim of the research project “Innovative Strategies for Observations in the Arctic Atmospheric Boundary Layer (ISOBAR)” is to substantially increase the understanding of the stable atmospheric boundary layer (SBL) through a combination of well-established and innovative observation methods as well as by models of different complexity. During three weeks in February 2017, a first field campaign was carried out over the sea ice of the Bothnian Bay in the vicinity of the Finnish island of Hailuoto. Observations were based on ground-based eddy-covariance (EC), automatic weather stations (AWS) and remote-sensing instrumentation as well as more than 150 flight missions by several different Unmanned Aerial Vehicles (UAVs) during mostly stable and very stable boundary layer conditions. The structure of the atmospheric boundary layer (ABL) and above could be resolved at a very high vertical resolution, especially close to the ground, by combining surface-based measurements with UAV observations, i.e., multicopter and fixed-wing profiles up to 200 m agl and 1800 m agl, respectively. Repeated multicopter profiles provided detailed information on the evolution of the SBL, in addition to the continuous SODAR and LIDAR wind measurements. The paper describes the campaign and the potential of the collected data set for future SBL research and focuses on both the UAV operations and the benefits of complementing established measurement methods by UAV measurements to enable SBL observations at an unprecedented spatial and temporal resolution.
Highlights
The atmospheric boundary layer (ABL) is the lowest part of the atmosphere where the Earth’s surface strongly influences the wind, temperature, and humidity through turbulent transport of air mass
The 3D-wind vector and the temperature measurements are capable of resolving turbulence up to frequencies of approximately 30 Hz, allowing turbulent fluctuations to be resolved in the sub-meter range
When the top of a thermally-stratified ABL fell within the sounding range, the pattern of echo-signal was used to determine the ABL height. The latter was determined by visual inspection of echograms and return-signal profiles, as the height where the echo intensity of a pronounced echoing layer sharply decreases. This method was chosen as the echo-intensity is a reliable indicator for mixing, in contrast to the standard deviation of the vertical velocity, σw, that is often wave-dominated in the stable boundary layer (SBL) and is not a proper indicator for turbulence
Summary
The atmospheric boundary layer (ABL) is the lowest part of the atmosphere where the Earth’s surface strongly influences the wind, temperature, and humidity through turbulent transport of air mass. Errors in h ABL might induce considerable uncertainties in the forecast of wind profiles and the location of low-level jets (LLJ), which are crucial parameters for applications such as wind energy This leads to a typical warm bias for SBL conditions in NWP models [4,7,8], which is of importance under the aspects of climate and climate change. The main idea is to combine the reliability and continuity of well-established ground-based observations with the flexibility of small UAV systems This strategy is to be applied during several campaigns in polar regions to provide extensive data sets on the turbulent structure of the SBL with unique and unprecedented spatial and temporal resolution.
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