Profiling the Arctic Stable Boundary Layer in Advent Valley, Svalbard: Measurements and Simulations
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The unmanned aerial system SUMO (Small Unmanned Meteorological Observer) has been used for the observation of the structure and behaviour of the atmospheric boundary layer above the Advent Valley, Svalbard during a two-week period in early spring 2009. Temperature, humidity and wind profiles measured by the SUMO system have been compared with measurements of a small tethered balloon system that was operated simultaneously. It is shown that both systems complement each other. Above 200 m, the SUMO system outperforms the tethered balloon in terms of flexibility and the ability to penetrate strong inversion layers of the Arctic boundary layer. Below that level, the tethered balloon system provides atmospheric profiles with higher accuracy, mainly due to its ability to operate at very low vertical velocities. For the observational period, a numerical mesoscale model has been run at high resolution and evaluated with SUMO profiles reaching up to a height of 1500 m above the ground. The sensitivity to the choice of atmospheric boundary-layer schemes and horizontal resolution has been investigated. A new scheme especially suited for stable conditions slightly improves the temperature forecast in stable conditions, although all schemes show a warm bias close to the surface and a cold bias above the atmospheric boundary layer. During one cold and cloudless night, the SUMO system could be operated nearly continuously (every 30–45 minutes). This allowed for a detailed case study addressing the structure and behaviour of the air column within and above Advent Valley and its interaction with the local topography. The SUMO measurements in conjunction with a 10-m meteorological mast enabled the identification of a very stable nocturnal surface layer adjacent to the valley bottom, a stable air column in the valley and a strong inversion layer above the summit height. The results indicate the presence of inertial-gravity waves during the night, a feature not captured by the model.
KeywordsAtmospheric profiles Boundary-layer schemes High-resolution numerical model Inertial-gravity oscillation Small Unmanned Meteorological Observer (SUMO) measurements Stable Arctic atmospheric boundary layer
The field work was financed by the Arctic Field Grant 2009 (Svalbard Science Forum RIS ID 3346). Travel expenses for the co-authors M. O. Jonassen and J. Reuder have been covered by Meltzerfondet and an IPY-Thorpex Norwegian Research Council grant number 175992/S30. Special thanks to Avinor at Longyearbyen airport for a cooperative working environment, and to meteorologikonsulent Torgeir Mørk (met.no) for kindly providing meteorological data from Longyear airport. The authors are grateful to UNIS for the accessibility of the old Auroral Station in Adventdalen. Thanks to Andøya Rocket Range for the permission to use their facilities at Longyear airport. Many thanks to Tor de Lange (GFI) for his great commitment in installing the weather mast in AV in extreme weather conditions. The tethered balloon data were kindly provided by Tiina Kilpeläinen and Miina Manninen. The authors wish to acknowledge the work and commitment of the pilots Martin Müller and Christian Lindenberg. We thank Thomas Spengler for the valuable discussions on boundary-layer dynamics of the case study. Supercomputing resources, on a Cray XT4 computer at Parallab at the University of Bergen, have been made available by the Norwegian Research Council. Finally, the authors are grateful to the three anonymous reviewers who distinctly improved the manuscript by constructive criticism. This is publication no. A 389 from the Bjerknes Centre for Climate Research.
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