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Page Title:
Formation Criteria for Mountain Waves |
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Formation Criteria for Mountain Waves. Several conditions must be present for a mountain wave to form. They are as follows:The component of the wind perpendicular to the mountain ridge at the mountain top level must be 25 knots or greater. Table 6-1-3.-Low-level-Wind-Induced Turbulence Thresholds
The wind direction must be within 50 from the perpendicular to the mountain range (ridge line). The closer the direction to perpen-dicular, the stronger the wave. On the leeward (downwind) side of the mountain, the atmosphere should be adiabatically stable or there must be an inversion present that extends at least up to the height of the mountain peaks. This stability or an inversion prevents convective instability from breaking up the wave pattern. This also implies that low-level convective clouds should never be observed when a mountain wave exists. There should be a rapid increase in wind speed with altitude from the level of the mountain peak to several thousand feet above the mountain peak. Above this, there should be a steady strong flow up to the tropopause, with speeds increasing gradually. A very rapid increase all the way to the tropopause can eliminate the wave. A jet stream will frequently be located over the mountain range when mountain wave turbulence is observed. |
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