A Numerical Study of the Terrain Effects on a Squall Line


Observations indicate that some squall line systems moving from the Taiwan Strait towards the mountains would decrease in intensity and dissipate. Obviously the terrain effects on the squall lines are very important. A two-dimensional terrain following coordinated cloud model was used to study geographical effects on a squall line. In the model the moutain peak was assumed to be 1 or 2 km in height with the squall line forming over the plain area and propagating towards the mountains. In the plain area new convection continually formed on the forward side of the squall line so that the squall line could maintain itself. When the squall line moved over mountainous areas it slowed down and began decreasing its intensity due to the weakness of new convection. The decrease in intensity resulted from less moisture flowing into the squall line at the higher altitude. The terrain effect on the restriction of the development of the squall line was more evident the higher the mountain.

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