TITLE

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

AUTHOR(S)
Zängl, Günther; Chimani, Barbara; Häberli, Christian
PUB. DATE
January 2004
SOURCE
Monthly Weather Review;Jan2004, Vol. 132 Issue 1, p368
SOURCE TYPE
DOC. TYPE
Article
ABSTRACT
This paper presents numerical simulations of the MAP IOP 10 foehn case (24 October 1999) for the lower Alpine Rhine Valley, which was one of the two target areas selected for foehn observations. The simulations have been performed with a modified version of the fifth-generation Pennsylvania State Universityâ€“NCAR Mesoscale Model MM5. Most importantly, the horizontal diffusion of temperature and the mixing ratios of water vapor and cloud water is computed truly horizontally rather than along the model surfaces, as is the case in the original MM5. In the Rhine Valley, the foehn case under consideration was characterized by a complex and rapidly changing flow field. In the early morning, the foehn was restricted to the upper parts of the valley while a cold air pool was present in the lower parts and around the exit toward Lake Constance. During the following hours, the cold air pool was gradually eroded, and the foehn reached Lake Constance around noon. Only 3 h later, a shallow cold front passing from the west terminated the foehn at Lake Constance and in the adjacent parts of the Rhine Valley. The cold front then gradually moved up the Rhine Valley and lifted the warm foehn air off the ground. With the modified model version, the observed flow evolution could be reproduced essentially correctly. Discrepancies between model results and observations are largely restricted to small errors in the time of foehn breakthrough and in the time of the cold front passage. In agreement with observations, the simulations show a pronounced downvalley increase of the surface potential temperature. The highest potential temperatures as well as the highest surface wind speeds are attained around Vaduz (Liechtenstein). The high wind speeds appear to be related to a complex three-dimensional gravity wave field excited over the adjacent mountain ridges. The downvalley increase of the surface potential temperature can be partly traced back to turbulent vertical mixing of stably stratified air. In addition, advection of potentially warm air from an adjacent mountain range is found in the region around Vaduz. Sensitivity experiments with the original diffusion scheme show much larger discrepancies between model results and observations. Because the temperature diffusion along the coordinate surfaces tends to dissipate the initial cold air pool, the foehn breakthrough toward Lake Constance is simulated several hours too early. Reducing the horizontal resolution by a factor of 3 while retaining the modified diffusion scheme has a less detrimental effect on the model results than computing the diffusion along the coordinate surfaces.
ACCESSION #
11912140

## Related Articles

• Diffusion mechanism of water vapour in a zeolitic tuff rich in clinoptilolite. Çakıcğlu-Ozkan, F.; Ülkü, S. // Journal of Thermal Analysis & Calorimetry;Dec2008, Vol. 94 Issue 3, p699

The adsorption kinetics of H2O in a clinoptilolite rich zeolitic tuff was experimentally investigated at 18Â°C. In the identification of the diffusion mechanism the isothermal adsorption model equation was used. It was found out that the intraparticle mass transfer becomes more dominant over...

• Technical Note: Characterization of a static thermal-gradient CCN counter. Frank, G. P.; Dusek, U.; Andreae, M. O. // Atmospheric Chemistry & Physics;2007, Vol. 7 Issue 12, p3071

The static (parallel-plate thermal-gradient) diffusion chamber (SDC) was one of the first instruments designed to measure cloud condensation nuclei (CCN) concentrations as a function of supersaturation. It has probably also been the most widely used type of CCN counter. This paper describes the...

• Investigation of the physical origins of etching LiNbO3 during Ti in-diffusion. Sivan, Vijay; Holland, Anthony; O'Mullane, Anthony P.; Mitchell, Arnan // Applied Physics Letters;3/22/2010, Vol. 96 Issue 12, p121913

We investigate the physical origins of etching observed during Ti diffusion. The relationship between observed etch depth and water vapor content in the annealing environment is quantified. The dynamics of the etching process are also identified. It is discovered that water vapor content is...

• Sorption and diffusion of water vapour on edible films. Berkün, D.; Balköse, D.; Tıhmınlıoǧlu, F.; Altınkaya, S. // Journal of Thermal Analysis & Calorimetry;Dec2008, Vol. 94 Issue 3, p683

Two types of films consisting of sodium salt of carboxymethyl cellulose (NaCMC) and hydroxypropyl cellulose (HPC) as film forming materials and glycerin as plasticizer were prepared, characterized and their water vapour sorption properties were determined. The water sorption isotherms of the...

• The remote impacts of climate feedbacks on regional climate predictability. Roe, Gerard H.; Feldl, Nicole; Armour, Kyle C.; Hwang, Yen-Ting; Frierson, Dargan M. W. // Nature Geoscience;Feb2015, Vol. 8 Issue 2, p135

Uncertainty in the spatial pattern of climate change is dominated by divergent predictions among climate models. Model differences are closely linked to their representation of climate feedbacks, that is, the additional radiative fluxes that are caused by changes in clouds, water vapour, surface...

• The Nature, Significance and Control of Solar-Driven Water Vapor Diffusion in Wall Systems--Synthesis of Research Project RP-1235. Derome, Dominique; Karagiozis, Achilles; Carmeliet, Jan // ASHRAE Transactions;2010, Vol. 116 Issue 1, p572

A project initiated by TC 4.4 looked at the nature, significance and control of solar-driven water vapor diffusion in wall systems. The project combined experimental and simulation work to provide an in-depth characterization of the phenomena occurring during inwards vapor diffusion in insulated...

• Definition of "banner clouds" based on time lapse movies. Schween, J. H.; Kuettner, J.; Reinert, D.; Reuder, J.; Wirth, V. // Atmospheric Chemistry & Physics;2007, Vol. 7 Issue 8, p2047

Banner clouds appear on the leeward side of a mountain and resemble a banner or a flag. This article provides a comprehensive definition of "banner clouds". It is based primarily on an extensive collection of time lapse movies, but previous attempts at an explanation of this phenomenon are also...

• Time Variability of Surface-Layer Characteristics over a Mountain Ridge in the Central Himalayas During the Spring Season. Solanki, Raman; Singh, Narendra; Kiran Kumar, N.; Rajeev, K.; Dhaka, S. // Boundary-Layer Meteorology;Mar2016, Vol. 158 Issue 3, p453

We present the diurnal variations of surface-layer characteristics during spring (March-May 2013) observed near a mountain ridge at Nainital ( $$29.4^{\circ }\mathrm{N},\,79.5^{\circ }\mathrm{E},$$ 1926 m above mean sea level), a hill station located in the southern part of the central...

• Orographic Flow Response to Variations in Upstream Humidity. Reeves, Heather Dawn; Rotunno, Richard // Journal of the Atmospheric Sciences;Nov2008, Vol. 65 Issue 11, p3557

The effects of upstream relative humidity (RH) on low-level wind and precipitation patterns for low-speed, statically stable flows over a mountain are investigated using idealized two- and three-dimensional numerical-simulation experiments in which RH is increased from 0% to 100%. For RH less...

Share