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

Drobinski, Philippe; Steinacker, Reinhold; Richner, Hans; Baumann‐Stanzer, Kathrin; Beffrey, Guillaume; Bénech, B.; Berger, Heinz; Chimani, Barbara; Dabas, Alain; Dorninger, Manfred; Dürr, Bruno; Flamant, Cyrille; Frioud, Max; Furger, Markus; Gröhn, Inga; Gubser, Stefan; Gutermann, Thomas; Häberli, Christian; Häller-Scharnhost, Esther; Jaubert, Geneviève; Lothon, Marie; Mitev, Valentin; Pechinger, U.; Piringer, Martin; Ratheiser, Matthias; Ruffieux, Dominique; Seiz, Gabriela; Spatzierer, Manfred; Tschannett, Simon; Vogt, S.; Werner, R.; Zängl, Günther

doi:10.1002/qj.70

Cited by 44 publications

(46 citation statements)

References 48 publications

(94 reference statements)

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“…Time series of 2-m air temperature data recorded at different altitudes around the city, and simulation results from high-resolution mesoscale simulations are used. In this study, we used the MesoNH numerical model (Lafore et al, 1998) that has already been successfully used to model stable ABL (e.g., Martínez et al, 2010) and valley or basin winds (e.g., Flamant et al, 2002;Drobinski et al, 2007).…”

Section: Introductionmentioning

confidence: 99%

The Atmospheric Boundary Layer during Wintertime Persistent Inversions in the Grenoble Valleys

Largeron

Staquet

2016

Front. Earth Sci.

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This study addresses the atmospheric boundary layer dynamics in the Grenoble valleys during persistent inversions, for 5 months during the 2006-2007 winter. During a persistent inversion, the boundary layer contains a layer with a positive vertical temperature gradient over a few days. Temperature data recorded on the valley sidewalls are first used. A bulk measure of the boundary layer stability, based upon the temperature difference between the valley top and the valley bottom, is introduced and a criterion is proposed to detect persistent inversions. We show that this criterion is equivalently expressed in terms of the heat deficit inside the boundary layer. Nine episodes are detected and coincide with the PM 10 -polluted periods of the 2006-2007 winter. Secondly, the five strongest and longest persistent inversions are simulated using the MesoNH model. Focus is made on the stagnation stage of the episode, during which the inversion exhibits a diurnal cycle that does not significantly evolve from day to day. Whatever the episode, the inversion develops from the ground over a height of about 1200 m, with a nighttime temperature strength reaching 20 K. The boundary-layer dynamics within the inversion layer are fully decoupled from the (anticyclonic, weak) synoptic flow, independent from the synoptic-wind direction and similar whatever the episode. This implies that these dynamics are controlled by thermal winds and solely depends upon the geometry of the topography and upon the radiative cooling of the ground. Finally, a 2-day high-resolution simulation is made for the strongest case, representative of any persistent inversion. The flow pattern displays a well-defined spatial structure, with a vertical layering resulting from the superposition of the down-valley winds flowing from the different valleys surrounding Grenoble. This pattern persists all day long over a shallow convective layer of about 50 m forming above the ground during the reduced daytime period. Within this shallow layer, convection triggers a weak up-valley wind. Ventilation and stagnation areas in the surface layer are also computed, providing insights for air quality studies. The main characteristics of these persistent inversions are comparable to the most extreme wintertime inversions recorded in the Grand Canyon, Arizona.

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Section: Introductionmentioning

confidence: 99%

The Atmospheric Boundary Layer during Wintertime Persistent Inversions in the Grenoble Valleys

Largeron

Staquet

2016

Front. Earth Sci.

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“…Dynamically driven winds, including Föhn winds, in which the synoptic flow interacts with terrain (Drobinski et al, 2007;Campana et al, 2005;Lothon et al, 2003).…”

Section: Introductionmentioning

confidence: 99%

Surface-to-mountaintop transport characterised by radon observations at the Jungfraujoch

et al. 2014

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Abstract. Atmospheric composition measurements at Jungfraujoch are affected intermittently by boundary-layer air which is brought to the station by processes including thermally driven (anabatic) mountain winds. Using observations of radon-222, and a new objective analysis method, we quantify the land-surface influence at Jungfraujoch hour by hour and detect the presence of anabatic winds on a daily basis. During 2010-2011, anabatic winds occurred on 40 % of days, but only from April to September. Anabatic wind days were associated with warmer air temperatures over a large fraction of Europe and with a shift in air-mass properties, even when comparing days with a similar mean radon concentration. Excluding days with anabatic winds, however, did not lead to a better definition of the unperturbed aerosol background than a definition based on radon alone. This implies that a radon threshold reliably excludes local influences from both anabatic and non-anabatic vertical-transport processes.

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“…Recent field campaigns have specifically addressed some of these issues for several different topographic environments (e.g. Mobbs et al, 2005;Mayr et al, 2007;Drobinski et al, 2007;Grubišić et al, 2008). The present case study is a contribution to this field of research, with specific regard to the Adriatic bora windstorm that occurs on the leeward side of the Dinaric Alps.…”

Section: Introductionmentioning

confidence: 99%

On the onset of bora and the formation of rotors and jumps near a mountain gap

Gohm

Mayr

Fix³

et al. 2008

Quart J Royal Meteoro Soc

125

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This study investigates the onset phase of a strong Adriatic bora windstorm that occurred on 4 April 2002. The target area is a gap about 20 km wide embedded in the coastal mountain barrier of the Dinaric Alps that favours strong jet-like winds. Airborne-aerosol back-scatter lidar measurements on board the DLR Falcon research aircraft, together with surface and upper-air observations, are used to verify high-resolution numerical experiments conducted with the mesoscale atmospheric model RAMS and a single-layer shallow-water model (SWM). Especially during the breakthrough phase of the bora, the flow at the gap exit exhibits a complex spatial structure and temporal evolution. On a transect through the centre of the gap, a hydraulic jump forms; this is located close to the coast throughout the night, and starts to propagate downstream in the early morning. On a transect through the edge of the gap, a lee-wave-induced rotor becomes established, due to boundary-layer separation. It starts to propagate downstream about two hours after the jump. This flow evolution implies that the onset of strong winds at the coast occurs several hours earlier downstream of the centre of the gap than downwind of the edge of the gap. Consequently, the wind field in the vicinity of Rijeka airport, located downwind of the gap, is strongly inhomogeneous and transient, and represents a potential hazard to aviation. Measured bora winds at the surface exceed 20 ms −1 , and the simulated wind speed in the gap wind layer exceeds 30 ms −1 . The simulated turbulent kinetic energy exceeds 10 m 2 s −2 .RAMS indicates that wave-breaking near a critical level is the dominant mechanism for the generation of the windstorm. Gap jets can be identified downstream of several mountain passes. The simulated wave pattern above the Dinaric Alps, the wave decay with height due to directional wind shear and the strong flow descent on the leeward side of the barrier are supported by measured back-scatter intensities. Basic bora flow features, including gap jets and jumps, are remarkably well reproduced by SWM simulations. The RAMS reference run captures observed flow phenomena and the temporal flow evolution qualitatively well. A cold low-level bias, an overestimated bora inversion strength, and a slightly too-early bora onset are probably related to insufficient turbulent mixing in the boundary layer. The amplitude of trapped gravity waves, the time of the bora breakthrough and the inversion strength are found to be quite sensitive to the turbulence parametrization.

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

Cited by 44 publications

References 48 publications

The Atmospheric Boundary Layer during Wintertime Persistent Inversions in the Grenoble Valleys

The Atmospheric Boundary Layer during Wintertime Persistent Inversions in the Grenoble Valleys

Surface-to-mountaintop transport characterised by radon observations at the Jungfraujoch

On the onset of bora and the formation of rotors and jumps near a mountain gap

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