From the Sky Above Mountains into their Depths

The Alps are an important field of study for both geophysicists and meteorologists at the University of Vienna. The first group of researchers uses physical methods to analyse hitherto unexplored depths underneath the mountains, while the others record the unique characteristics of mountain weather and phenomena of climatic relevance.

Feb. 1, 2016

The geological history of the Alps is relatively well known: Several million years ago, the Earth’s crust began rising as the result of a collision of the African and the European continents – and Europe’s largest mountain chain is still rising. This sometimes results in earthquakes, which can be registered with highly sensitive seismometers. However, geophysics can also use the seismic waves generated by earthquakes to explore unexplored depths of the Earth’s interior. The Research Group Geophysics led by Götz Bokelmann has already successfully used seismic waves to reconstruct large-scale deformation patterns in the subsurface of the Alps.

Geophysics plays an important role in finding and dealing with natural resources and in understanding environmental and societal hazard issues such as seismic hazards.”

Götz Bokelmann, Professor of Geophysics

The researchers were able to determine these deformations based on what is called “seismic anisotropy”: As a result of geodynamic processes and the deformations caused by them, mineral crystals orient themselves in certain direction inside the Earth. Their preferred orientation, in turn, influences physical properties, e.g. the characteristic double refraction of seismic waves. Based on the direction and speed with which the waves spread, “we can deduce the deformation geometry of the material in the Earth’s interior,” says Götz Bokelmann. He was, for example, able to show that the orientation of the crystals in the subsurface of the Alps is largely aligned with the mountain chain’s topography, i.e. mainly the mountain ridges. “This is one of the clearest examples of mountain-chain-parallel anisotropy worldwide,” says the geophysicist. The researchers also found systematic deviations that have not yet been explained. The study, which was published in 2014, has raised questions that are currently being studied in the large-scale European project AlpArray.

Seismology and safety

Modern geophysical methods allow researchers to gain insights into Europe’s largest mountain chain in a way that has so far never been possible in the two centuries in which the Alps have been studied. AlpArray, which involves 18 countries, aims to use geophysics to survey the subsurface of the Alps more accurately than ever before. The Department of Meteorology and Geophysics is coordinating Austria’s contribution to this project. AlpArray Austria is funded by the Austrian Science Fund (FWF). In 2015, a temporary network of mobile seismometers covering all of Austria was set up. Over the next two years, these seismological stations will record even the most minute ground motion data. “The data gathered in this project will also help us understand the earthquake hazard better,” says Bokelmann.

Using geophysical methods to answer questions relevant to society is another goal of Bokelmann’s Group: Currently, the team is, for example, assessing the seismic hazard in different regions of Austria, particularly in the larger Vienna region. In order to be able to evaluate the risk of future earthquakes, they examine stalagmites, i.e. stone formations that rise from cave floors, in flowstone caves. “If the stalagmites are intact, this means that in the last 10,000 to 20,000 years no earthquake has been strong enough to topple the stalagmites,” the researcher explains. Based on the numerical modelling of their results, the team can determine the risk of earthquakes. Other projects include the development of geophysical methods that can be used to prove that nuclear weapon tests have been carried out underground (in cooperation with the Comprehensive Nuclear Test Ban Treaty Organization CTBTO). Furthermore, the team uses geophysical methods to evaluate the potential risks of different kinds of energy extraction, e.g. the recovery of natural gas from shale rock, or fracking.

Atmospheric analyses

The Research Group General Meteorology and Climatology at the Department of Meteorology and Geophysics specialises in weather phenomena in the mountains, particularly the Alpine region. The Group, which is led by Reinhold Steinacker, focuses particularly on diagnostic modelling, i.e. the question of how the current weather can be determined with maximum precision. To this end, the researchers have developed the Vienna Enhanced Resolution Analysis (VERA) method, “a pioneering project for the diagnostic high-resolution modelling in mountainous areas that has gained international recognition,” says Steinacker.

Simply put, VERA can be used to analyse the weather in the Alpine region in real time. The system calculates the spatial distribution of air pressure, temperature, wind and precipitation and removes erroneous data automatically. It recognises both systematic errors caused by wrongly calibrated instruments and random errors resulting from transmission problems. VERA is, for example, used by the Austrian aviation weather service. Steinacker’s Group is particularly interested in the small-scale features of meteorological phenomena. The measuring instruments are installed at short distances, sometimes only 2 km, creating a dense network of surface stations in the areas they are surveying. In contrast, global weather models generally get their data from stations located at intervals of 25 to 30 km. “It has recently been shown that the integration of small-scale regional data sets into global models can have a positive impact on the quality of their forecasts,” says Steinacker.

Our objective is to improve weather forecasts. We focus on diagnostic modelling, because the better we know the current weather, the better we can predict what it will be like in the future.”

Reinhold Steinacker, Professor of General Meteorology

One of the special characteristics of mountain weather are so-called cold air pools. They can form temporarily in Alpine valleys and basins but particularly in dolines – characteristic sink-holes in limestone. Cold pools in such dolines are known for their extremely low minimum temperatures. A doline in the Ybbstal Alps at approx. 1,300 m is known for its historical record of -52.6°C, which is the coldest temperature ever measured in Central Europe. In a current project, the researchers have been able to determine that winter temperatures in the doline have not come close to the temperature in the record year 1932 over the last 10 to 15 years. One suspected reason for this – in addition to global warming – is a feedback loop between biosphere and atmosphere. Extremely low temperatures and a deep snowpack of up to 3.5 m are specific challenges for every measurement system. Manfred Dorninger, a member of the Group, developed the so-called MetLift system. It adapts the height of the sensors according to the snow depth automatically. This avoids snow-covering of the sensors. A prototype of the energy self-sufficient system is operated at the Trafelberg in Lower Austria since a couple of years.

Numerical models and climate research

The Research Group Theoretical Meteorology focuses particularly on the observation and numerical modelling of how air flows over and around mountains. Another research topic is the diagnostic measurement of climate changes and climate anomalies. In several FWF projects and the large-scale EU project ERA-CLIM2, meteorologist Leopold Haimberger is working on correcting data of the global radiosonde network in order to make it better suited for creating global atmospheric climate analyses over several decades. Climate analyses is used to measure global and regional energy transports between the atmosphere and the oceans. An understanding of these processes is fundamental for understanding changes in the climate system. Significant contributions have been made to relevant climate reports such as the IPCC report and the Austrian APCC report.