Gap Winds in the Strait of Juan de Fuca

Overland, James E.; Walter, Bernard A.

doi:10.1175/1520-0493(1981)109<2221:gwitso>2.0.co;2

Cited by 73 publications

(66 citation statements)

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“…Due to the combined channelling and sloping effects, shallow föhn bears some similarity to the wind systems that occurred in the Stampede Gap and on the lee side of the Cascade Range, Washington State (Colle and Mass 1998a,b) and in the Lut Valley and Jaz Murian dry lake, Iran (Liu et al 2000). However, due to the short length of the Wipptal (¼35 km between Brenner Pass and Innsbruck), shallow föhn also exhibits fundamental differences from the ows documented in these studies as well as with 'classical' sea-level gap ows such as those observed in Cook Inlet and Shalikof Strait, Alaska (Lackmann and Overland 1989;Macklin et al 1990;Bond and Stabeno 1998), in Fraser Gap and the Strait of Juan de Fuca of Washington State and British Columbia (Overland and Walter 1981;Mass 1995, 2000), in Howe Sound, British Columbia (Jackson and Steyn 1994a), in the Strait of Gibraltar (Scorer 1952) and in the Isthmus of Tehantepec in Mexico (Steenburgh et al 1998). For example, the crossgap Rossby number, R D V l=f L 2 (where V is the along-gap wind speed, l and L the cross-and along-gap length-scales and f is the Coriolis parameter- Overland (1984)) associated with the Wipptal setting is typically ¼1 (see appendix for a detailed scale analysis of shallow föhn in the Wipptal).…”

Section: Introductionmentioning

confidence: 70%

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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Section: Introductionmentioning

confidence: 70%

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

“…In Howe Sound, the synoptic situation o f several outflow events is described by Jackson and Steyn (1994a), Jackson (1996), and Finnigan et al (1994). At the surface, a similar situation was found in all cases that are similar to the first case described earlier in Overland and Walter (1981). An arctic high pressure advanced from the Yukon Territory toward southern BC, blocked by the coastal mountains, and an associated arctic front moved across Howe Sound.…”

Section: I2i Synoptic-scale Pressure Gradientsupporting

confidence: 57%

“…Three outflow events in Juan de Fuca Strait have been studied by Overland and Walter (1981). They explain the different synoptic features that were responsible for the outflow cases.…”

Section: I2i Synoptic-scale Pressure Gradientmentioning

confidence: 99%

“…According to the principles o f fluid dynamics, the pressure must drop in the area where the width of the cross-section decreases causing the strongest speeds (Sharp and Mass, 2004). flows is the acceleration down the pressure gradient (Overland and Walter, 1981;Mass et al, 1995;Colie and Mass, 2000;Sharp and Mass, 2004;Koletsis et al, 2009). …”

Section: I23i Venturi Effectmentioning

confidence: 99%

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Strong Along-Channel Winds on the Coast of British Columbia: Synoptic Climatology and Case Studies.

Bakri¹

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“…The interaction of the coastal ocean and atmosphere, which occurs mainly through the turbulent exchange processes, depends on scales of motion from the synoptic to the smallest turbulence scales. At the synoptic scale, land-fallng storms and barrier effects are important (Hobbs et al, 1980;Overland and Walter, 1981;Mass and Ferber, 1990). In mid-latitudes, atmospheric waves may be trapped in the dense marine layer where this layer intersects coastal mountains (Beardsley et al, 1987;Dorman 1985Dorman , 1987Zemba and Friehe, 1987).…”

Section: Appendix 4: Interior Water Column Processesmentioning

confidence: 99%

Coastal ocean processes : wind-driven transport processes on the U.S. west coast : Portland, Oregon, Workshop July 14-16, 1993

Smith¹,

Brink²

1994

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Gap Winds in the Strait of Juan de Fuca

Cited by 73 publications

References 0 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

Strong Along-Channel Winds on the Coast of British Columbia: Synoptic Climatology and Case Studies.

Coastal ocean processes : wind-driven transport processes on the U.S. west coast : Portland, Oregon, Workshop July 14-16, 1993

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