Orographic Effect Animation. The sequence of frames portrays a westerly wind, blowing onshore from the Pacific Ocean, driven by a large low-pressure system over the northwestern US. At point 1, the airmass is relatively warm (about 23 degrees C) and moisture laden (relative humidity about 80%) blowing over the ocean surface. At point 2 the airmass rises over the California Coast Range, cools to about 17 degrees C, and its relative humidity reaches 100%, so that clouds form and it rains, loosing some of the moisture it is carrying. At point 3, the air has sunk into the Central Valley, warming nearly to its original temperature. However, because the airmass lost moisture over the Coast Range, it now has a lower relative humidity. At point 4, the airmass is forced to rise over the higher Sierra Nevada range, cooling progressively as it rises in elevation from 3000 feet (12 degrees C) to over 14000 feet (freezing point). Initially, moisture is lost as rain at lower elevations and then snow at the high elevations. Much of the moisture is wrung out over the Sierra Nevada such that when the air sinks into the low-lying (near sea level) Owens Valley to the east, it warms (to about 16 degrees C) and consequently has a very low moisture content and relative humidity. Position 6 illustrates rising air over the White Mountains, about 10,000 feet high, over which the air again cools and loses what little moisture it has as snow. As the air descends into the desert region of Nevada, it warms again with a very low moisture content and relative humidity. To watch the animation again from the beginning, just refresh your brower.
Originally uploaded in Integrate:Teaching for Sustainability:InTeGrate Modules:Water Science and Society:Student Materials.
Image 150182 is a 414 by 700 pixel WebP
Uploaded:
Mar28 17
