16.05.2019 Kolloquium: Dr. Helen C. Ward
Helen C. Ward
Department of Atmospheric and Cryospheric Sciences, University of Innsbruck, Austria
16:15- 17:15 Uhr
In mountainous terrain urban areas represent regions of high population density that are frequently exposed to adverse weather (e.g. downslope windstorms, heavy snowfall) and poor air quality. Understanding turbulent exchange in such areas is of great importance to human health and well-being, as accurate representation of urban surface processes in numerical models is necessary for weather forecasting and pollutant dispersion modelling. However, most of our current knowledge, and therefore most of the physics behind mesoscale models, relies on theory that was developed for flat and horizontally homogeneous landscapes. In this talk, I will present recent work investigating the extent to which complex environments conform (or do not conform) to current theory.
Situated in the Austrian Alps, the city of Innsbruck (approx. 600 m above sea level) is surrounded by mountains on either side of the city reaching over 2000 m (peak-to-peak distance across the Inn Valley is about 20 km). Eddy covariance measurements of heat, water and carbon dioxide exchange are conducted at the Innsbruck Atmospheric Observatory (IAO) on the roof of the university building close to the city centre. Observations at different levels offer insight into the variation of turbulence characteristics with height and the possible impact of local building effects. Comparison with flux measurements outside the city reveals the influence of urban characteristics and human behaviour on surface exchange. For example, limited vegetation within the city restricts the evaporation rate and carbon dioxide uptake compared to surrounding non-urban areas. Shading by orography (or, within the street canyon, by buildings) modifies the incoming shortwave radiation, thus affecting the available energy particularly for low sun angles. The complex landscape around Innsbruck generates substantial spatial variation in radiation, flow and turbulent exchange. Particularly during foehn, considerable differences are seen in temperature, humidity and wind direction, as well as in turbulent exchange, depending on the timing and location of foehn breakthrough.
A combination of long-term measurements and model simulations are used to examine turbulent exchange across a range of conditions in and around Innsbruck. Each study is focused on identifying relevant physical processes in order to improve understanding of how complex environments differ from horizontally homogeneous and flat landscapes.
16. Mai 2019