On the Stagnant Zone Upstream of an Obstacle within a Stably Stratified Flow in the Atmosphere

Kitabayashi, Koji

doi:10.2151/jmsj1965.59.3_373

Cited by 4 publications

(2 citation statements)

References 15 publications

(11 reference statements)

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“…He used the wind-tunnel test-section depth in defining his Froude number, but concluded that a critical Froude number based on the barrier height should be adopted. His data (Kitabayashi 1981 ; figure 19) can be used to support the argument for a critical Froude number for upstream blocking, based on hill height, of F x 1.0.…”

Section: -2mentioning

confidence: 88%

“…However, the approach wind profile was not uniform and the density profile was not linear, so the Froude numbers he calculated are not directly comparable to those of more idealized laboratory studies. Kitabayashi (1981) continued his studies of stratified flow over two-dimensional objects by analysing the flow over thin, vertical barriers. He used the wind-tunnel test-section depth in defining his Froude number, but concluded that a critical Froude number based on the barrier height should be adopted.…”

Section: -2mentioning

confidence: 99%

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The structure of strongly stratified flow over hills: dividing-streamline concept

et al. 1985

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In stably stratified flow over a three-dimensional hill, we can define a dividing streamline that separates those streamlines that pass around the hill from those that pass over the hill. The height Hs of this dividing streamline can be estimated by Sheppard's simple energy argument; fluid parcels originating far upstream of a hill at an elevation above Hs have sufficient kinetic energy to rise over the top, whereas those below Hs must pass around the sides. This prediction provides the basis for analysing an extensive range of laboratory observations and measurements of stably stratified flow over a variety of shapes and orientations of hills and with different upwind density and velocity profiles. For symmetric hills and small upwind shear, Sheppard's expression provides a good estimate for Hs. For highly asymmetric flow and/or in the presence of strong upwind shear, the expression provides a lower limit for Hs. As the hills become more nearly two-dimensional, these experiments become less well defined because steady-state conditions take progressively longer to be established. The results of new studies are presented here of the development of the unsteady flow upwind of two-dimensional hills in a finite-length towing tank. These measurements suggest that a very long tank would be required for steady-state conditions to be established upstream of long ridges with or without small gaps and cast doubt upon the validity of previous laboratory studies.

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Section: -2mentioning

confidence: 88%

Section: -2mentioning

confidence: 99%

The structure of strongly stratified flow over hills: dividing-streamline concept

et al. 1985

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Surface airflow around Windless Bight, Ross Island, Antarctica

O'Connor

Bromwich

1988

Quart J Royal Meteoro Soc

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SCJMMARYRoss Island, Antarctica is located along the Transantarctic Mountains and is subjected to a strong southerly mountain-parallel wind regime. Despite this, Windless Bight on the island's southern coast is a region of anomalous calm. The atmospheric boundary layer dynamics that gives rise to this phenomenon is analysed both theoretically and observationally. It is the strong static stability of the boundary layer air encountering the high steep topography of' Ross Island, that causes a stagnation zone resulting in the calm conditions of Windless Bight.Direct and proxy observations of boundary layer winds provide a detailed description of airflow around the island. The anomalous (with respect to the synoptic pressure field) but persistent north-easterly winds at Scott Base are due to the deflection of highly stable, low-level air around Hut Point Peninsula. By contrast, the less frequent, strong southerly winds which override the peninsula are associated with the influx of warm maritime air from cyclonic systems to the east. It is inferred that flow of air around the terrain of Ross Island gives rise to locally strong winds; these are responsible for the ice breakout and polynya occurrences in McMurdo Sound.Thc surface airflow past Ross Island can be modelled by a two-dimensional, steady, frictionless, irrotational, incompressible flow past an obstacle, with a shape bascd on an island height contour. The flow is assumed to separate from the eastern and western sides of the island and form a wake downstream. A solution for this flow is presented, based on potential theory for streaming motion past an obstacle. The streamline and isobar patterns clearly depict the stagnation region in Windless Bight. For approaching winds of 20 m s ' thc local pressure field is perturbed by several millibars.

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