Quarterly Journal of the Royal Meteorological Society, 2007
This paper summarizes the findings of seven years of research on föhn conducted within the projec... more This paper summarizes the findings of seven years of research on föhn conducted within the project 'Föhn in the Rhine Valley during MAP' (FORM) of the Mesoscale Alpine Programme (MAP). It starts with a brief historical review of föhn research in the Alps, reaching back to the middle of the 19th century. Afterwards, it provides an overview of the experimental and numerical challenges identified before the MAP field experiment and summarizes the key findings made during MAP in observation, simulation and theory. We specifically address the role of the upstream and cross-Alpine flow structure on föhn at a local scale and the processes driving föhn propagation in the Rhine Valley. The crucial importance of interactions between the föhn and cold-air pools frequently filling the lower Rhine Valley is highlighted. In addition, the dynamics of a low-level flow splitting occurring at a valley bifurcation between the Rhine Valley and the Seez Valley are examined. The advances in numerical modelling and forecasting of föhn events in the Rhine Valley are also underlined. Finally, we discuss the main differences between föhn dynamics in the Rhine Valley area and in the Wipp/Inn Valley region and point out some open research questions needing further investigation.
Quarterly Journal of the Royal Meteorological Society, 2006
The föhn/cold-pool interactions in the lower Alpine Rhine valley documented in the framework of t... more The föhn/cold-pool interactions in the lower Alpine Rhine valley documented in the framework of the Intensive Observing Period (IOP) 15 of the Mesoscale Alpine Programme (MAP) on 5 November 1999 are analysed. The present study focuses on the water vapour mixing ratio measurements acquired with the airborne differential absorption lidar LEANDRE 2 which enabled detailed documentation of the along-valley structure of the cold pool. LEANDRE 2 and microbarograph measurements revealed the presence of Kelvin-Helmholtz waves (KHW) at the top of the cold pool. The characteristics of the waves were different in the region of the coldpool leading edge (the southernmost part of the cold pool) and in the vicinity of the Bodensee (Lake Constance), further to the north. Gravity waves were also observed above the cold pool in the in situ aircraft data acquired in the vicinity of the Bodensee. The gravity waves are suspected to be triggered by the KHW at the top of the cold pool. We also investigate the respective role of the three known processes likely to control the structure of the cold pool and its erosion along the Rhine valley, namely (i) convection within the cold pool, (ii) turbulent erosion at the top of the cold pool due to the presence of KHW, and (iii) dynamic displacement of the cold pool by föhn air. The former two processes are likely not to play a role in the erosion of the cold pool observed in the course of this IOP. Finally, the temporal evolution of the heat budget advection term in the lower Rhine valley was investigated using temperature profiles derived from balloon soundings acquired at two sites which were overpassed by the cold-pool edge in the course of its displacement northwards during the early afternoon as the result of the action of the föhn, and then southwards in the late afternoon as the föhn weakened and cold air from the Bodensee area was filling the lower Rhine Valley.
... This yields a more realistic and detailed analysis of the meteorological fields such as press... more ... This yields a more realistic and detailed analysis of the meteorological fields such as pressure, temperature and wind fields (see also extended abstract 3.04 by Bica et al. and Bica et al. (2005)). ... Cold front approaching Klagenfurt (red arrow) from NW. Klagenfurt Page 3. ...
Quarterly Journal of the Royal Meteorological Society, 2007
This paper summarizes the findings of seven years of research on föhn conducted within the projec... more This paper summarizes the findings of seven years of research on föhn conducted within the project 'Föhn in the Rhine Valley during MAP' (FORM) of the Mesoscale Alpine Programme (MAP). It starts with a brief historical review of föhn research in the Alps, reaching back to the middle of the 19th century. Afterwards, it provides an overview of the experimental and numerical challenges identified before the MAP field experiment and summarizes the key findings made during MAP in observation, simulation and theory. We specifically address the role of the upstream and cross-Alpine flow structure on föhn at a local scale and the processes driving föhn propagation in the Rhine Valley. The crucial importance of interactions between the föhn and cold-air pools frequently filling the lower Rhine Valley is highlighted. In addition, the dynamics of a low-level flow splitting occurring at a valley bifurcation between the Rhine Valley and the Seez Valley are examined. The advances in numerical modelling and forecasting of föhn events in the Rhine Valley are also underlined. Finally, we discuss the main differences between föhn dynamics in the Rhine Valley area and in the Wipp/Inn Valley region and point out some open research questions needing further investigation.
9 radiosonde stations, 2 wind profilers, 4 Doppler sodars, 2 scintillometers, 1 scanning and 1 ba... more 9 radiosonde stations, 2 wind profilers, 4 Doppler sodars, 2 scintillometers, 1 scanning and 1 backscatter lidar and different research aircraft. This paper gives an overview of the objectives of FORM, describes the target area and its instrumentation, and provides a detailed synoptic description of the 12 foehn cases observed during the MAP SOP.
Quarterly Journal of the Royal Meteorological Society, 2007
This paper summarizes the findings of seven years of research on föhn conducted within the projec... more This paper summarizes the findings of seven years of research on föhn conducted within the project 'Föhn in the Rhine Valley during MAP' (FORM) of the Mesoscale Alpine Programme (MAP). It starts with a brief historical review of föhn research in the Alps, reaching back to the middle of the 19th century. Afterwards, it provides an overview of the experimental and numerical challenges identified before the MAP field experiment and summarizes the key findings made during MAP in observation, simulation and theory. We specifically address the role of the upstream and cross-Alpine flow structure on föhn at a local scale and the processes driving föhn propagation in the Rhine Valley. The crucial importance of interactions between the föhn and cold-air pools frequently filling the lower Rhine Valley is highlighted. In addition, the dynamics of a low-level flow splitting occurring at a valley bifurcation between the Rhine Valley and the Seez Valley are examined. The advances in numerical modelling and forecasting of föhn events in the Rhine Valley are also underlined. Finally, we discuss the main differences between föhn dynamics in the Rhine Valley area and in the Wipp/Inn Valley region and point out some open research questions needing further investigation.
Quarterly Journal of the Royal Meteorological Society, 2006
The föhn/cold-pool interactions in the lower Alpine Rhine valley documented in the framework of t... more The föhn/cold-pool interactions in the lower Alpine Rhine valley documented in the framework of the Intensive Observing Period (IOP) 15 of the Mesoscale Alpine Programme (MAP) on 5 November 1999 are analysed. The present study focuses on the water vapour mixing ratio measurements acquired with the airborne differential absorption lidar LEANDRE 2 which enabled detailed documentation of the along-valley structure of the cold pool. LEANDRE 2 and microbarograph measurements revealed the presence of Kelvin-Helmholtz waves (KHW) at the top of the cold pool. The characteristics of the waves were different in the region of the coldpool leading edge (the southernmost part of the cold pool) and in the vicinity of the Bodensee (Lake Constance), further to the north. Gravity waves were also observed above the cold pool in the in situ aircraft data acquired in the vicinity of the Bodensee. The gravity waves are suspected to be triggered by the KHW at the top of the cold pool. We also investigate the respective role of the three known processes likely to control the structure of the cold pool and its erosion along the Rhine valley, namely (i) convection within the cold pool, (ii) turbulent erosion at the top of the cold pool due to the presence of KHW, and (iii) dynamic displacement of the cold pool by föhn air. The former two processes are likely not to play a role in the erosion of the cold pool observed in the course of this IOP. Finally, the temporal evolution of the heat budget advection term in the lower Rhine valley was investigated using temperature profiles derived from balloon soundings acquired at two sites which were overpassed by the cold-pool edge in the course of its displacement northwards during the early afternoon as the result of the action of the föhn, and then southwards in the late afternoon as the föhn weakened and cold air from the Bodensee area was filling the lower Rhine Valley.
... This yields a more realistic and detailed analysis of the meteorological fields such as press... more ... This yields a more realistic and detailed analysis of the meteorological fields such as pressure, temperature and wind fields (see also extended abstract 3.04 by Bica et al. and Bica et al. (2005)). ... Cold front approaching Klagenfurt (red arrow) from NW. Klagenfurt Page 3. ...
Quarterly Journal of the Royal Meteorological Society, 2007
This paper summarizes the findings of seven years of research on föhn conducted within the projec... more This paper summarizes the findings of seven years of research on föhn conducted within the project 'Föhn in the Rhine Valley during MAP' (FORM) of the Mesoscale Alpine Programme (MAP). It starts with a brief historical review of föhn research in the Alps, reaching back to the middle of the 19th century. Afterwards, it provides an overview of the experimental and numerical challenges identified before the MAP field experiment and summarizes the key findings made during MAP in observation, simulation and theory. We specifically address the role of the upstream and cross-Alpine flow structure on föhn at a local scale and the processes driving föhn propagation in the Rhine Valley. The crucial importance of interactions between the föhn and cold-air pools frequently filling the lower Rhine Valley is highlighted. In addition, the dynamics of a low-level flow splitting occurring at a valley bifurcation between the Rhine Valley and the Seez Valley are examined. The advances in numerical modelling and forecasting of föhn events in the Rhine Valley are also underlined. Finally, we discuss the main differences between föhn dynamics in the Rhine Valley area and in the Wipp/Inn Valley region and point out some open research questions needing further investigation.
9 radiosonde stations, 2 wind profilers, 4 Doppler sodars, 2 scintillometers, 1 scanning and 1 ba... more 9 radiosonde stations, 2 wind profilers, 4 Doppler sodars, 2 scintillometers, 1 scanning and 1 backscatter lidar and different research aircraft. This paper gives an overview of the objectives of FORM, describes the target area and its instrumentation, and provides a detailed synoptic description of the 12 foehn cases observed during the MAP SOP.
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Papers by S. Tschannett