Comparison of Horizontal and Vertical Scintillometer Crosswinds during Strong Foehn with Lidar and Aircraft Measurements

Furger, Markus; Drobinski, Philippe; Prévôt, Andrê S. H.; Weber, Rudolf O.; Graber, Werner K.; Neininger, B.

doi:10.1175/1520-0426(2001)018<1975:cohavs>2.0.co;2

Cited by 15 publications

(5 citation statements)

References 23 publications

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“…6) as often observed in föhn ows (e.g. Hoinka 1985;Heimann 1992;Furger et al 2001). The large downward motion observed by the NOAA P-3 near Nösslachjoch (most marked at 2400 m a.s.l.)…”

Section: (B) Along Valleymentioning

confidence: 58%

Gap flow in an Alpine valley during a shallow south föhn event: Observations, numerical simulations and hydraulic analogue

Flamant¹,

Drobinski

Nance

et al. 2002

Quart J Royal Meteoro Soc

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SUMMARYThis paper examines the three-dimensional structure and dynamics of southerly hybrid gap/mountain ow through the Wipp valley (Wipptal), Austria, observed on 30 October 1999 using high-resolution observations and model simulations. The observations were obtained during a shallow south föhn event documented in the framework of the Mesoscale Alpine Programme (MAP). Three important data sources were used: the airborne differential-absorption lidar LEANDRE 2, the ground-based Doppler lidar TEACO2 and in situ measurements from the National Oceanic and Atmospheric Administration P-3 aircraft. This event was simulated down to 2 km horizontal resolution using the non-hydrostatic mesoscale model Meso-NH. The structure and dynamics of the ow were realistically simulated. The combination of high-resolution observations and numerical simulations provided a comprehensive three-dimensional picture of the ow through the Wipptal: in the gap entrance region (Brenner Pass, Austria), the low-level jet was not solely due to the channelling of the southerly synoptic ow through the elevated gap. Part of the Wipptal ow originated as a mountain wave at the valley head wall of the Brenner Pass. Downstream of the pass, the shallow föhn ow had the characteristics of a downslope windstorm as it rushed down towards the Inn valley (Inntal) and the City of Innsbruck, Austria. Downhill of the Brenner Pass, the strongest ow was observed over a small obstacle along the western side wall (the Nösslachjoch), rather than channelled in the deeper part of the valley just to the east. Further north, the low-level jet was observed in the centre of the valley. Approximately halfway between Brenner Pass and Innsbruck, where the along-axis direction of the valley changes from north to north-north-west, the low-level jet was observed to be de ected to the eastern side wall of the Wipptal. Interaction between the Stubaier Alpen (the largest and highest topographic feature to the west of the Wipptal) and the south-westerly synoptic ow was found to be the primary mechanism responsible for the de ection. The along-and cross-valley structure and dynamics of the ow were observed to be highly variable due to the in uence of surrounding mountains, localized steep slopes within the valley and out ows from tributaries (the Gschnitztal and the Stubaital) to the west of the Wipptal.For that shallow föhn case, observations and simulations provided a large body of evidence that downslope ow created thinning/ thickening uid and accelerations/ decelerations reminiscent of mountain wave/hydraulic theory. Along the Wipptal, two hydraulic-jump-like transitions were observed and simulated, (i) on the lee slope of the Nösslachjoch and (ii) in the Gschnitztal exit region. A hydraulic solution of the ow was calculated in the framework of reduced-gravity shallow-water theory. The down-valley evolution of the Froude number computed using LEANDRE 2, P-3 ight level and TEACO2 measurements con rmed that these transitions were associated with super-to subcritical transitions.

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“…6) as often observed in föhn ows (e.g. Hoinka 1985;Heimann 1992;Furger et al 2001). The large downward motion observed by the NOAA P-3 near Nösslachjoch (most marked at 2400 m a.s.l.)…”

Section: (B) Along Valleymentioning

confidence: 58%

Gap flow in an Alpine valley during a shallow south föhn event: Observations, numerical simulations and hydraulic analogue

Flamant¹,

Drobinski

Nance

et al. 2002

Quart J Royal Meteoro Soc

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show abstract

“…This method was used to document the strong föhn wind storms of MAP IOP 8 to 10 (i.e. 20 to 24 October 1999) (Furger et al 2001).…”

mentioning

confidence: 99%

Scale interaction processes during the MAP IOP 12 south föhn event in the Rhine Valley

Drobinski

Haeberli

Richard

et al. 2003

Quart J Royal Meteoro Soc

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SUMMARYThis paper examines the three-dimensional structure and dynamics of a south föhn ow in the Rhine Valley during its entire life cycle from 29 October 1999 until 31 October 1999. The south föhn 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 föhn ow 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 föhn penetrating the FORM target area on 30 October 1999 is preceded by a nocturnal shallow föhn phase which does not penetrate down to the ground due to katabatic drainage ow from the main transverse (east-west oriented) tributaries in which föhn cannot penetrate. This paper shows the contribution of the main tributaries of the Rhine Valley in directing the föhn ow towards the FORM target area during (i) the shallow föhn phase where the westerly upper-level ow is de ected in the main longitudinal (i.e. north-south oriented) tributaries; (ii) the penetrating föhn phase, where the south/south-westerly upper-level ow is nearly aligned with the longitudinal tributaries. The channelling ef ciency of the main longitudinal tributaries of the Rhine Valley (particularly the Domleschg) is higher during the föhn phase when the south-westerly upper-level ow, experiencing mountain-wave-induced downward motion, penetrates these tributaries, than during the shallow föhn.In the FORM target area, the structure of the föhn ow varies on a 1-kilometre horizontal length-scale and the time evolution of the respective location of the cold air pool and the warm föhn air is investigated in detail. Also, ow splitting between the Rhine and Seez Valleys occurs during the entire föhn life cycle, but its vertical extension is maximum during shallow föhn, when lower-and upper-level ows are fully decoupled.

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“…Scintillometry, as a technique for providing spatially-integrated turbulence data, has been used successfully in complex terrain on several occasions [32,100,101]. Single wavelength methods typically yield path averaged fluxes or, more fundamentally, structure parameters over distances typically ranging from 500 m to 7 km.…”

Section: Active Remote Sensingmentioning

confidence: 99%

High-Resolution Observations of Transport and Exchange Processes in Mountainous Terrain

et al. 2018

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Mountainous areas require appropriate measurement strategies to cover the full spectrum of details concerning the energy exchange at the Earth’s surface and to capture the spatiotemporal distribution of atmospheric dynamic and thermodynamic fields over them. This includes the range from turbulence to mesoscale processes and its interaction. The surface energy balance needs appropriate measurement strategies as well. In this paper, we present an overview of important experiments performed over mountainous terrain and summarize the available techniques for flow and energy measurements in complex terrain. The description includes ground-based and airborne in situ observations as well as ground-based and airborne remote sensing (passive and active) observations. Emphasis is placed on systems which retrieve spatiotemporal information on mesoscale and smaller scales, fitting mountainous terrain research needs. Finally, we conclude with a short list summarizing challenges and gaps one faces when dealing with measurements over complex terrain.

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Comparison of Horizontal and Vertical Scintillometer Crosswinds during Strong Foehn with Lidar and Aircraft Measurements

Cited by 15 publications

References 23 publications

Gap flow in an Alpine valley during a shallow south föhn event: Observations, numerical simulations and hydraulic analogue

Gap flow in an Alpine valley during a shallow south föhn event: Observations, numerical simulations and hydraulic analogue

Scale interaction processes during the MAP IOP 12 south föhn event in the Rhine Valley

High-Resolution Observations of Transport and Exchange Processes in Mountainous Terrain

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