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Small-scale processes in complex terrain

Final Report Summary - ROTOR (Small-scale processes in complex terrain)

Both researchers and weather forecasters are becoming increasingly dependent on the ability of mesoscale numerical weather prediction models to provide an accurate representation of atmospheric phenomena. While high-resolution simulations provide an unprecedented level of detail in the depiction of atmospheric processes and phenomena, verifying their realism continues to represent a challenge, in particular in mountainous regions where mesoscale observational networks are fewer in
number and, where existent, they are of lower density than those over flat terrain. Consequently, relatively few high-resolution models have been evaluated in complex terrain.
In the ROTOR project, this challenge was addressed by carrying out a combined observational and numerical studies of small-scale processes in complex terrain over a wide range of atmospheric conditions and terrain configurations. The small-scale orographic phenomena under investigation included gap flows and flow channelling, atmospheric rotors, mountain waves and wakes. While these phenomena formed the general focus of the project, the specific case studies that were undertaken were dictated by the emergence of new observational data from the most recent field campaigns and topics of interest to particular students.
Research efforts supported by the the project include:
1. A study of the dynamics of a non-stationary atmospheric rotor observed in the lee of Wyoming's Medicine Bow Range, combining high-resolution numerical simulations with the analysis of data from an airborne dual-Doppler cloud radar.
2. A study of the interaction between atmospheric and oceanic wakes past the island of Madeira, also integrating numerical simulations with airborne in-situ observations of wind, temperature and humidity.
3. A modelling study of the propagation of a solitary atmospheric wave over the Gulf of Mexico.
4. The analysis of ground-based wind measurements with a profiling lidar in a wind park, located in an area with moderately complex topography in Lower Austria, with special focus on the characterization of wakes generated by wind turbines.
5. An idealized modelling study of the impact of large orographic obstacles on the intensity and the trajectory of single-cell and multicell convective storms.
6. A preliminary study of dynamically-forced westerly wind events in Owens Valley, in the lee of the Sierra Nevada in California. This effort builds on an extensive archive of ground-based and airborne observations collected during the 2008 T-Rex project. The numerical simulation of a selection of intensive observation periods of that project is undertaken here.

Most of the above-mentioned topics were the subject of one or more Master thesis projects. A limited number of graduate students was also supported. Each student received financial support at the minimum level of employment defined by the Austrian law, with an average contract duration of approximately one year. Work by the students and the supervisors led to the preparation of a significant number of contributions to national and international conferences, including the 4th Austrian Meteorology Day,
the annual meetings of the European Geophysical Union, the American Meteorological Society Annual Meeting and the Mountain Meteorology Conference, and the International Conference on Alpine Meteorology.

The publications and dissemination of results include Diploma (M.S.) thesis, conference poster and oral presentations, and four manuscripts submitted to the peer reviewed journals that were submitted after the end of the grant performance period.