Numerical Simulations of the Foehn in the Rhine Valley on 24 October 1999 (MAP IOP 10)

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104

ABSTRACT:The improvement of Quantitative Precipitation Forecasting (QPF) in mountainous regions was a major supporting objective of the Mesoscale Alpine Programme (MAP) project P1 devoted to the study of orographic precipitation. This paper reviews the main MAP-related achievements regarding QPF improvement and highlights the MAP impact on developing QPF research and planning future operational strategies. Recent results based on MAP case-studies, on data analysis and assimilation, on quantification of model uncertainties, and on model intercomparison and verification substantiate the progress made in recent years in improving model performance in relation to short-range, high-resolution forecasting in complex topography regions, well represented by the European Alps.

Section: Model Improvements Triggered By Mapmentioning

confidence: 94%

Quantitative precipitation forecasting in the Alps: The advances achieved by the Mesoscale Alpine Programme

Richard

Buzzi

Zängl³

2007

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104

“…The sub-kilometre resolution was found necessary in order to resolve fine-scale structures of the föhn flow and associated dynamical features such as hydraulic jumps (Jaubert and Stein, 2003). The föhn simulations of Zängl et al (2004a) indicate that mesoscale structures can successfully be simulated at moderate (1 km, in their case) horizontal resolution, but the details (e.g. nearsurface characteristics) exhibit considerable discrepancies between observation and simulation.…”

Section: Numerical Modellingmentioning

confidence: 99%

On the boundary‐layer structure over highly complex terrain: Key findings from MAP

Rotach

Zardi

2007

164

118

Within MAP, one of the scientific projects was devoted to 'Boundary Layers in Complex Terrain'. In a number of subprojects, boundary-layer issues were addressed and detailed high-resolution multi-sensor observations were combined with simulation by models allowing for adequate parametrization of turbulence processes. In this contribution, the projects are briefly introduced and an attempt is made to summarize their key findings and to put them into a joint perspective. Spatial variability is found to be large but strictly related to topography and therefore allowing for possible parametrization. Traditional boundary-layer scaling approaches cannot simply be applied over highly complex topography, but some of the MAP findings suggest the potential for suitable extensions of those scaling relations to cover various cases of complex terrain. The mean boundary-layer structure and thermally driven flows in narrow valleys are found not to be generally in line with previous results from larger valleys elsewhere. Furthermore, local circulations are reported to contribute considerably to exchange between valley and free troposphere. In particular, the range of their effects on the lower atmosphere seems to be larger than just turbulent transport within the planetary boundary layer would suggest. Thus in larger-scale numerical models where the topography is not resolved, possible sub-grid parametrizations for local exchange seem to be in order.

“…This was vital for the validation of the models. This network also contributed to the derivation of better initial conditions for research and NWP models (Zängl et al, 2004a;Jaubert et al, 2005) and the mesoscale analyzes extensively used for föhn investigations in the Rhine Valley (Drobinski et al, 2003a;Chimani et al, 2006;Flamant et al, 2006).…”

Section: Observation Networkmentioning

confidence: 99%

Föhn in the Rhine Valley during MAP: A review of its multiscale dynamics in complex valley geometry

Drobinski¹,

Steinacker²,

Richner³

et al. 2007

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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.