May 26 - July 31
Quantifying the Stable Boundary Layer Depth in the Arctic Region of Northern Finland
Theresa Lincheck, Brian R. Greene, Francesca M. Lappin, and Elizabeth A. Pillar-Little
What is already known:
- Stable boundary layers (SBL) form in the absence of surface heating from the sun and are often characterized by weak mechanical turbulence and strong temperature inversions.
- Stable boundary layers are currently not well understood and poorly modelled in weather prediction and climate models due to a lack of high resolution spatial and temporal atmospheric observations.
- Recent developments in Unmanned Aircraft Systems (UAS) make them a feasible option for profiling SBLs on much higher spatial and temporal resolutions than previously possible.
- Many discrepancies presently exist in SBL depth parametrizations, thus there is a need to better quantify the stable boundary layer depth.
What this study adds:
- Stable boundary layers formed in the Arctic region of northern Finland are analyzed via data collected during the 2018 ISOBAR field campaign.
- Temperature, windspeed, and wind direction profiles taken from a rotary-wing UAS developed by OU-CASS known as the CopterSonde are used as the main source to analyze characteristics of the SBL.
- Maximum potential temperature gradients and wind speeds from the CopterSonde are investigated as possible factors in determining realistic stable boundary layer depths.
- Potential temperature gradient maximums combined with horizontal wind speed and direction profiles from the CopterSonde show promise to determining realistic SBL depths, although further study is needed.
Abstract:
The complex structure of the nighttime Arctic stable boundary layer (SBL) has long impeded the development of a comprehensive SBL depth parametrization, consequently leading to poor representation in many climate models. This study attempts to quantify the depth of the SBL in the Arctic region of Finland using high-resolution vertical profile data of temperatures, horizontal wind speeds, and directions extrapolated from in-situ rotary-wing unmanned aircraft systems (rwUAS) flown during the 2018 Innovative Strategies for Observations in the Arctic Atmospheric Boundary Layer (ISOBAR) field campaign. Two SBL depth parametrizations are investigated — 1) the height of the maximum potential temperature gradient and 2) the height of the maximum horizontal wind speed magnitude, or lowest low-level jet height. Initial attempts at calculating a single consistent maximum temperature gradient proved difficult, and averaging and filtering methods were employed to improve chances of observing reasonable heights. The addition of horizontal wind directions as wind vectors to temperature profiles helped offer insights into the behavior of the inversions and confirm or invalidate the maximum gradient heights. Investigating maximum wind speed heights revealed they consistently formed around 80 m – 100 m above the maximum temperature gradient heights. Analyses of the three SBL profiles altogether — temperature, wind speed, and direction — propounded the possibility of their usage in creating a more explicit SBL depth parametrization. The results also demonstrated the capabilities of rwUAS as a promising tool for improving understandings of the SBL structure.