The Grünloch modeling study is a 2-year (July 2014 - June 2016) research project at the University of Utah, funded by the National Science Foundation, to investigate selected aspects of thermally driven flows and cold-air pool development in the Grünloch, a small sinkhole in the Austrian Alps. The project and the numerical model simulations are designed on the basis of findings from previous and ongoing field campaigns that have been conducted since 2001 by the University of Vienna in Austria (Dr. Manfred Dorninger and his research group). The focus of this project is on (i) the thermally driven cross-basin circulation and (ii) the nocturnal development of basin inversions and their interaction with cold-air outflows through gaps and saddles in the surrounding topography.
More details can be found in the NSF project proposal.
Principal investigators
Manuela Lehner (PI)
Dave Whiteman (Co-PI)
Collaborators
Manfred Dorninger (University of Vienna, Austria)
Presentations
Poster AMS Conference on Mountain Meteorology 2016, Burlington, VT
Poster International Conference on Alpine Meteorology 2015, Innsbruck, Austria
The Grünloch
The Grünloch basin is a small sinkhole on the Hetzkogel Plateau in the eastern Alps of Austria, with a diameter of approximately 1 km and a depth of about 150 m. It is surrounded by a continious ridgeline, with the highest peak reaching to about 400 m above the basin floor. The ridgeline is intersected by three major passes to the northwest, the southwest, and the east-southeast, with the lowest pass at a height of about 50 m above the basin floor. Meteorological research has a long history in the Grünloch and its immediate surroundings, going back to the late 1920s. The Grünloch and other sinkholes on the Hetzkogel Plateau are known for the formation of strong nocturnal temperature inversions and extreme temperature minima, including the minimum temperature record for central Europe with -52.6°C at the bottom of the Grünloch.
Research questions and results
Model simulations are performed with the CM1 model (CM1 website by George Bryan (NCAR)).
Cold-air pool development
Temperature inversions, that is an increase of temperature with height, form regularly during clear-sky nights due to cooling of the ground. In mountain valleys and closed basins, particularly strong temperature inversions can form, which may even last for multiple days, particularly during the wintertime. Since inversions strongly inhibit vertical mixing, their presence can lead to the accumulation of air pollutants in large, inhabited valleys, where sources of air pollution are located. Previous observations in the Grünloch have shown that very strong inversions can form in the relatively shallow sinkhole, particularly in the lowest approximately 50 m above the basin floor, that is below the height of the lowest gap in the surrounding topography. At the top of this strong temperature inversion an outflow of air through the gap has been observed. One major goal of the present project was to further investigate the development of the temperature inversion in the Grünloch, the characteristics and physics of the cold-air outflow over the saddle, and the effect of the outflow on the temperature inversion.
Animation showing the build-up of the temperature inversion in a vertical cross section through the basin from northwest to southeast.
Animation showing the flow through a gap in the topography to the northwest of the basin. The horizontal cross section is at a height just above the saddle.
Thermally driven cross-basin circulation
Thermally driven cross-basin circulations develop due to asymmetries in solar irradiation between opposing basin sidewalls. The resulting temperature difference causes a flow toward the more irradiated sidewall. Previous wintertime observations in the Grünloch have indicated the presence of cross-basin circulations in the sinkhole. The goal of this project is to investigate the effect of time of year and vegetation cover on the cross-basin circulation in the Grünloch.