The Fahn Effect

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Foehn effect. Topography requires the mass of air rising, condensing water vapor and causing orographic rainfall (barrier effect). Downwind air dry and falls off rapidly rising barometric pressure and temperature (Foehn effect).
The Foehn effect F hn or (name taken from a German wind characteristic of northern Alps) occurs in mountainous terrain where a mass of warm and moist air is forced to rise to save this obstacle. This causes the water vapor cools and undergoes a process ofcondensation or sublimation reverse precipitation in the windward slopes where orographic form clouds and rain. When this happens there is a sharp contrast between these slopes climate with high humidity and rainfall in the windward and leeward where the weather is clear and the temperature is increased by the process of adiabatic compression. This process is motivated because the dry, warm air and falls quickly by the side, warming up as we descended, and with a very low humidity. The effect Foen is the process described in the leeward slopes and turns out to be a wind drying and very hot. Puerto Cabello (Venezuela), is called Calderetas for this reason, the winds coming from the south (of the Plains and Lake Valencia) when down to the coast of the Central Coast. Very often, all moisture from the windward slopes do not become clouds and rain, but much of these clouds passing towards the leeward side, which "spread" with a completely reverse process happened in windward. In effect, orographic clouds descended on the leeward side is heated and its relative humidity decreases but not absolute, it remains the same.

by Kim MitzoThompson and Karen Mitzo Hilderbrand (Audio Cassette – Aug 31, 1999)