__Hydraulic
Jump Phenomenon__

where N is the Brunt-VŠisala Frequency (static stability parameter) and V is the
wind determined from the synoptic scale pressure gradient.

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If the Froude number is equal to or slightly greater
than 1, then there is the likelihood of mountain wave activity

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If the Froude number is less than one, then the
airflow is insufficient to carry the flow over the mountain and the flow is
blocked

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If Froude number is much more than 1, airflow
proceeds right over the mountain and down the other side, with no significant
oscillations

Fr at 1 or slightly greater than 1
occurs when the stable layer depth is near the top of
the blocking mountains, but not at the top.

When this occurs horizontal pressure gradient accelerations
are greatly augmented between the top of the mountain and the top of the stable
layer. Downwind of the mountain
crest, negative vertical pressure gradient accelerations far exceed horizontal
pressure gradient accelerations leading to acceleration downslope resulting in
horizontal speeds two to three times the strength of the synoptic scale wind
speeds.

At some distance from the mountain crest, the upward portion
of the oscillation creates upward directed vertical pressure gradient
accelerations that far exceed the horizontal pressure gradient accelerations
leading to a jump in the vertical velocities called the hydraulic jump
phenomenon (ground based mountain wave) but small horizontal wind speeds.