A Numerical Study of the Local Downslope Wind &amp;ldquo;Yamaji-kaze&amp;rdquo; in Japan

Saitō, Kazuo

doi:10.2151/jmsj1965.71.2_247

Cited by 45 publications

(1 citation statement)

References 34 publications

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“…This local downslope wind has been reported by previous studies (e.g., Owada 1990;Takane et al 2017). In general, winds descend easily where a col is present in mountainous areas (e.g., Lilly and Klemp 1979;Smith 1985;Saito 1993). An additional analysis of days with clear-sky conditions and a southerly wind (not a westerly wind) blowing over the Nobi Plain (5, 8, and 9 August 2015) showed the opposite results, with the potential temperature and wind speed observed at Ogaki being lower than those observed at Maibara (not shown).…”

Section: A Field Experimentsmentioning

confidence: 99%

Foehnlike Wind with a Traditional Foehn Effect plus Dry-Diabatic Heating from the Ground Surface Contributing to High Temperatures at the End of a Leeward Area

Takane

Kumakura

Kusaka

et al. 2017

Journal of Applied Meteorology and Climatology

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A foehn wind is an important factor in the occurrence of many extreme high-temperature events in geographically complex regions. In this study, the authors verified the hypothesis that a foehnlike wind contributes to high temperatures at the end of the leeward (eastward) area using three difference approaches: field experiments, numerical experiments, and statistical analyses. According to the hypothesis, a foehnlike wind has the features of the sum of a traditional foehn effect with adiabatic heating, plus dry-diabatic heating from the ground surface along the fetch of the wind. Field experiments conducted at seven observational points on Nobi Plain, Japan, where a mesoscale westerly wind blew, revealed that the westerly wind clearly had the features of a traditional foehn effect in the western part of the Nobi Plain. In addition to field experiments, a simplified estimate using a simple mixed-layer model demonstrated that the wind was further heated by dry-diabatic heating (sensible heat supply) from the ground surface along the fetch (especially in urbanized areas in the eastern region of the Nobi Plain) of the wind. This diabatic heating effect along the fetch of the wind on the high temperature at the end of the leeward area was also supported by both additional numerical experiments and a statistical analysis. These results proved that the hypothesis is correct and indicated that ground conditions and the land use and land cover in the windward area were strongly related to air temperature at the end of the leeward area, where an extremely high temperature was observed.

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Section: A Field Experimentsmentioning

confidence: 99%

Foehnlike Wind with a Traditional Foehn Effect plus Dry-Diabatic Heating from the Ground Surface Contributing to High Temperatures at the End of a Leeward Area

Takane

Kumakura

Kusaka

et al. 2017

Journal of Applied Meteorology and Climatology

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A climatological study of the strongest local winds of Japan “Inami‐kaze”

Koyanagi

Kusaka

2019

Intl Journal of Climatology

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This study examines the meteorological and climatological features of the Inami‐kaze in the Tonami Plain, the strongest local winds in Japan. The plain faces the Sea of Japan on the north side, while the remaining three sides are surrounded by high mountain ranges. An interview survey to local residents and the distribution of windbreak trees both indicate that the Inami‐kaze is localized to a surprisingly small region near the Inami town (about 6 km parallel to the mountain ridge and 3 km perpendicular to it), at the base of a very small saddle‐like topography in the mountain ridge. Wind statistics with a dense observation network during 2006–2014 (28 Inami‐kaze events) supports the above finding. Indeed, the wind speed is mostly (95%) below 11 m/s at the Tonami town, just 5 km away from the Inami town, while the Inami‐kaze (≥15 m/s) blows at the Inami town. Such a spatial pattern should be formed as a result of downslope windstorm with hydraulic jumps, which is indicated from the internal Froude number change across the mountain (0.9 at the upstream, 1.4 at the mountain top, and 0.3 at downstream). The required synoptic atmospheric condition for the Inami‐kaze is the pressure pattern “extratropical cyclone in the Sea of Japan.” The sufficient condition is the SSW–SSE wind (≥25 m/s) or south wind (around 20 m/s) at the 800‐pressure level over the mountain chain, indicating the allowed directional window is very narrow. On the other hand, the Inami‐kaze has an aspect of foehn. While the Inami‐kaze occur, the potential temperature at the Inami town tends to be higher by 4.7 K on average than in the windward plain on the Pacific Ocean side.

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Rotational aspects of stratified gap flows and shallow föhn

Sprenger

Schär

2001

Quart J Royal Meteoro Soc

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Observations of föhn in the Alps and other mountainous regions suggest that the underlying dynamics is often affected by gap‐like features in elongated ridge‐like topography. To assess the dynamics of these flows, idealized numerical experiments are conducted with a hydrostatic numerical model, using f‐plane geometry and a free‐slip lower boundary condition. The topography is taken to be a two‐dimensional ridge oriented in the west/east direction with a valley transect of depth ΔH across it. The upstream flow is westerly, with a constant wind speed U and constant Brunt‐Väisälä frequency N. The control parameters defined by this setting are a dimensionless gap depth NΔH/U, the ratio between ridge height and gap depth H/ΔH, a Rossby number describing the south‐north width of the ridge, and additional parameters associated with the shape of the gap. With intermediate Rossby numbers (Ro≈︁1) the setting resembles that of shallow Alpine south‐föhn cases, which are characterized by a cross‐Alpine flow essentially confined to valley transects. For small dimensionless gap depths and large Rossby numbers, the flow follows the predictions of linear theory and takes on an approximately symmetric pattern with respect to the ridge line. For NΔH/U ≳ 1, flow separation and splitting takes place upstream and downstream of the gap, respectively. The flow within the gap decouples from the flow aloft and is driven by the geostrophic south‐north pressure gradient to yield a föhn‐like flow. It is demonstrated that the limit f → 0 is singular (i.e. the flow solution does not converge towards the symmetric f = 0 solution), and that there exist multiple stationary solutions for f = 0 (two with northerly and southerly flow across the gap, respectively, and one with north/south symmetry). The existence of these multiple steady states is related to a wake instability, yet vortex shedding is suppressed by the presence of the ridge downstream of the gap. Additional simulations are presented which demonstrate that a transient external forcing can induce transitions between the multiple flow solutions. The relationship of the idealized setting to Alpine shallow föhn is discussed, and additional experiments are conducted to assess the effects of surface friction and of an inversion present to the south of the ridge.

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A Numerical Study of the Local Downslope Wind “Yamaji-kaze” in Japan

Cited by 45 publications

References 34 publications

Foehnlike Wind with a Traditional Foehn Effect plus Dry-Diabatic Heating from the Ground Surface Contributing to High Temperatures at the End of a Leeward Area

Foehnlike Wind with a Traditional Foehn Effect plus Dry-Diabatic Heating from the Ground Surface Contributing to High Temperatures at the End of a Leeward Area

A climatological study of the strongest local winds of Japan “Inami‐kaze”

Rotational aspects of stratified gap flows and shallow föhn

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