Scale interaction processes during the MAP IOP 12 south fošhn event in the Rhine Valley
- Author(s)
- Philippe Drobinski, Christian Häberli, Evelyne Richard, Marie Lothon, Alain Dabas, Pierre Henri Flamant, Markus Furger, Reinhold Steinacker
- Abstract
This paper examines the three-dimensional structure and dynamics of a south fošhn flow in the Rhine Valley during its entire life cycle from 29 October 1999 until 31 October 1999. The south fošhn event was documented in the framework of the Mesoscale Alpine Programme (MAP). This study investigates the synoptic-scale forcing sources, the dynamical processes driving the circulation of the fošhn flow in the complex network of tributaries of the Rhine Valley, and the degree of inhomogeneity on the scale of the FORM ('FOehn in the Rhine Valley during the MAP' programme) target area at the bifurcation between the Rhine and Seez Valleys. Several important data sources were used (ground-based Doppler lidar, scintillometers, constant-volume balloons, radiosoundings and surface stations) as well as non-hydrostatic mesoscale simulations. The fošhn penetrating the FORM target area on 30 October 1999 is preceded by a nocturnal shallow fošhn phase which does not penetrate down to the ground due to katabatic drainage flow from the main transverse (east-west oriented) tributaries in which fošhn cannot penetrate. This paper shows the contribution of the main tributaries of the Rhine Valley in directing the fošhn flow towards the FORM target area during (i) the shallow fošhn phase where the westerly upper-level flow is deflected in the main longitudinal (i.e. north-south oriented tributaries; (ii) the penetrating fošhn phase, where the south/south-westerly upper-level flow is nearly aligned with the longitudinal tributaries. The channelling efficiency of the main longitudinal tributaries of the Rhine Valley (particularly the Domleschg) is higher during the fošhn phase when the south-westerly upper-level flow, experiencing mountain-wave-induced downward motion, penetrates these tributaries, than during the shallow fošhn. In the FORM target area, the structure of the fošhn flow varies on a 1-kilometre horizontal length-scale and the time evolution of the respective location of the cold air pool and the warm fošhn air is investigated in detail. Also, flow splitting between the Rhine and Seez Valleys occurs during the entire fošhn life cycle, but its vertical extension is maximum during shallow fošhn, when lower- and upper-level flows are fully decoupled.
- Organisation(s)
- Department of Meteorology and Geophysics
- External organisation(s)
- Université Paris VI - Pierre-et-Marie-Curie, Université Toulouse III Paul Sabatier, Laboratoire d'Aérologie, Centre national de recherches météorologiques (CNRM), Laboratoire de Météorologie Dynamique, Paul Scherrer Institute
- Journal
- Quarterly Journal of the Royal Meteorological Society: a journal of the atmospheric sciences, applied meteorology, and physical oceanography
- Volume
- 129
- ISSN
- 0035-9009
- Publication date
- 2003
- Peer reviewed
- Yes
- Austrian Fields of Science 2012
- 1030 Physics, Astronomy
- Portal url
- https://ucrisportal.univie.ac.at/en/publications/scale-interaction-processes-during-the-map-iop-12-south-fohn-event-in-the-rhine-valley(594c4929-8cab-461c-9338-5bc324fbf235).html