Closing the Water Vapor Exchange Budget between the Ice Sheets and Free Atmosphere: A pilot study for the use of drones

Recent studies have shown that the Greenland Ice Sheet is continuously exchanging with water vapor in the atmosphere, resulting in post-depositional changes in the surface snow water isotope signal. However, it is unclear how the ice sheet communicates with the atmosphere through the PBL, which exchanges water vapor with the free troposphere. Quantifying the amount of water vapor lost to the free troposphere will help to constrain ice sheet mass balance, which is determined by net sublimation and accumulation via precipitation and condensation. These factors are poorly constrained in the interior of Greenland, currently confined to satellite data at low spatial and vertical resolution. Continuous vapor measurements have been made up to 7 m above the surface of the ice sheet, demonstrating that the humidity and isotopic signal of atmospheric water vapor experiences diurnal- and synoptic-scale variations. However, we are still lacking information about atmospheric humidity and isotope signals above 7 m and extending through the PBL.

During the summer 2018 field season at the EGRIP (North-East Greenland) field site, an Unmanned Aerial Vehicle (UAV) was used to measure atmospheric conditions up to 500 m above the surface of the ice sheet, to complement tower vapor measurements up to 7 m. An multi-rotor UAV was equipped with a temperature and humidity sensor, as well as glass flasks which collect atmospheric samples at different heights via remote control. Temperature and humidity data are used to identify the PBL and observe diurnal- and synoptic-scale changes in its height, and isotope data is valuable for interpreting the mass and isotope exchange between the ice sheet and the atmosphere. Preliminary results demonstrate changes in the height and structure of the PBL over the course of diurnal- and synoptic-scale cycles.

Determining the source, variability, and transport of water vapor in the different layers of the atmosphere will contribute to our understanding of how the isotopic value of atmospheric water vapor is imprinted on surface snow. In combination with in-situ near-surface atmospheric measurements, we will obtain a more complete picture of how atmospheric processes interact with the ice sheet, and will enhance our ability to interpret the water isotope signal in ice cores.