APRI members Wolfgang Schöner and Jonathan Fipper spent three weeks in the High North in August 2023. During this time, they collected data about the vertical temperature structure of the near-surface atmospheric boundary layer in the vicinity of the Villum Research Station by using Unmanned Aerial Vehicles (UAV).
The location of Station Nord close to the Villum Research Station, in the Northeast Greenland. (© Google)
The vertical structure of temperature and humidity in the tropospheric boundary layer – the lowest part of the atmosphere which is in exchange with the surface – has various effects on the ecosystem and physical conditions such as the snow cover or the surface melt of arctic glaciers and the Greenland Ice Sheet. In addition, vertical temperature gradients control the atmospheric stability and the mixing of air masses and are thus important for the spread of aerosols and air pollution. Air temperature inversions – rising temperatures with altitude – represent highly stable stratification and suppress vertical mixing and are thereby of particular scientific relevance. Unfortunately, these effects are hard to measure and to model, which is needed e.g., to predict effects of climate change on snow- and ice melt or ecology. The technical evolution of UAVs and their huge potential to explore the atmosphere, however, set a new milestone for improving this research. By conducting an UAV based method and in continuing previous research on other places in Greenland, two researchers from University of Graz did an extensive measuring campaign on the vertical temperature structure of the near-surface atmospheric boundary layer in the Arctic.
Villum Research Station (© Wolfgang Schöner)
Vertical temperature gradients are on a large spatial scale controlled by synoptic meteorological processes but at the Earth surface they are modified by the regional topography and different surface properties, which can be locally highly variable. Snow and ice surfaces reflect due to their high albedo large amounts of the incoming solar radiation and cannot exceed 0°C. Additionally, snow and ice surfaces are perfect emitters of longwave radiation which results in loss of energy, particularly during the polar night. In contrast, the snow free tundra absorbs a lot more solar radiation and can thus heat up significantly. The resulting temperature differences at the surface force temperature differences in the atmosphere as well depending on the surface properties. In addition, the interplay of near-surface temperature differences can generate wind systems like the katabatic wind resulting from the downflow from glaciers and ice caps of the comparably cold and heavy air masses over ice. Extremes of the katabatic wind are observed around the Greenland Ice Sheet. The relatively warmer air masses above the tundra tend to convection (rise of comparably warmer and lighter air masses). The different thermal reaction of the tundra relative to the ocean water is also a pre-condition for the land-sea-breeze system. In a warming and changing Arctic with e. g., decreasing snow covers, the vertical atmospheric structures are also matter of change and will interplay with various related processes.
Jonathan landing the drone. (© Wolfgang Schöner)
Villum Research Station/Study Area
Station Nord, the northernmost Danish military base is located in northeast Greenland on 81° North in Crown Prince Christian Land on the Princess Ingeborg Peninsula. With five soldiers permanently onsite, Station Nord is one of the worlds northernmost settlements. Next to the 70 years old military base, which is run since 1975 by the Danish Military, the Villum Research Station (VRS) is located. The VRS is managed by the University of Aarhus and was established by a donation of the Villum Fund in 2015. The surrounding terrain is rather flat with the largest ice cap in Greenland – Flade Isblink – being located 15 km south of the Station. Due to the very cold polar tundra climate with average temperatures in summer below 5°C, the tundra is just sparsely vegetated. Several atmospheric monitoring programs such as the Integrated Carbon Observation System (ICOS) or the WMO-Global Atmosphere Watch are operating around VRS with large series of permanently installed measurements. With having ice-free lakes and some ice-free sea water around in summer as well as the easily accessible ice cap with its marine terminating outlet glaciers and the vast tundra areas, VRS is a very suitable place for many disciplines of research.
View of the study area from Flade Isblink (left), Station Nord (right). (© Wolfgang Schöner)
Measurement Campaign at the Villum Research Station
Radiosondes (weather balloons) are still a key source for measuring vertical physical structures of the atmosphere and thus for weather prediction. They also play an important role for the so-called climate reanalysis, which makes a best estimate from “merging” observations with models for the past. However, radiosondes lack in spatial resolution and accuracy near the surface. Other methods measuring vertical structures of the atmosphere are generally rather demanding on energy, weight, or other challenges. UAVs can very easily measure atmospheric variables in high spatial resolution also near the ground.
To enhance the understanding of vertical atmospheric structures, this measurement campaign used quadcopter drones equipped with a sensor measuring temperature, humidity, air pressure, altitude, and the geographical coordinates every second. To quantify the influence of different surface properties on the high-arctic boundary layer, vertical measurements were made over open sea water, an ice-free freshwater lake, an outlet glacier of Flade Isblink and above the tundra.
A typical situation of the different vertical temperature structures over an outlet glacier of Flade Isblink and the Tundra (measured at August 2nd 2023) (left © Jonathan Fipper), Measuring points (right © Wolfgang Schöner).
Although weather conditions did not allow daily UAV flights, more than 100 profiles were collected in different meteorological conditions with ambient air temperatures ranging between -2°C and 11°C. An 80m high meteo-mast and various other permanently installed atmospheric measurements around VRS will help to better understand the UAV measurements in the context of different weather patterns and the related surface energy balance. Furthermore, they offer the valuable opportunity to validate the accuracy of the innovative UAV measurement approach against permanently installed measurements on the meteo-mast.
Jonathan flying the drone (left), The values measured by the drone are compared with the values measured at the same time on the 80m meteo mast. (right). (© Wolfgang Schöner)
But not just the UAVs had to struggle with certain weather conditions. The two researchers’ flight back to Svalbard was cancelled several times, forcing them to stay there longer than planned. This extended the measurement campaign by more than a week.
What we can learn from the measurements
Back in Graz, the analysis of the measurements will help to better understand the impact of different weather patterns on the atmospheric temperature structure from the combined analysis with reanalysis data, which helps to see the local and near-surface structures for the background of larger scale atmospheric patterns. It can also be inferred how representative the observed structures are for the VRS area (Princess Ingeborg Peninsula). Furthermore, the data could contribute to the improvement of future reanalysis products by providing typical near-surface temperature profiles for Northern Greenland during the summer season.
Written by Jonathan Fipper and Wolfgang Schöner.
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Photos: © Wolfgang Schöner.