In certain favorable localities, local winds are generated by immediate influences of the surrounding terrain, local winds are of environmental importance in various ways. They may exert a powerful stress on animals and plants, when the winds are dry and extremely hot or cold. they are also important in affecting the movement of atmospheric pollutants and in some localities carry pollution plumes far down-winds from the sources.
One class of local winds-sea breezes and land breezes. The cooling sea breeze (or lake breeze) of summer is an important environmental resource of coastal communities, for it adds to the attraction of the shore zone as a recreation facility.
Mountain and valley winds are local winds following a daily alternation of direction in a manner similar to the land and sea breezes. The air moves from valleys, upward over rising mountain slopes, toward the summits during the day, when slopes are intensely heated by the sun. The air then moves valley ward, down the ground slopes, when the same slopes have been cooled at night by radiation of heat from ground to air. These winds are therefore responding to local pressure gradients set up by heating or cooling of the lower air.
Still another group of local winds are known as drainage winds, or katabatic winds, in which cold air flows under the influence of gravity from higher to lower regions. Such cold, dense air may accumulate in winter over a high plateau or high interior valley. When general weather conditions are favorable some of their cold air spills over low divides or through passes to flow out upon adjacent lowlands as a strong, cold wind. Drainage winds occur in many mountainous regions of the world and go by various local names. The Bora of the northern Adriatic coast and the mistral of southern France are well-known examples. In southern California there issues on occasion from the Santa Ana Valley a strong, dry east wind, the Santa Ana, which blows across the coastal lowland. This air is of desert origin and may carry much dust and silt in suspension. On the ice caps of Greenland and Antarctica, powerful katabatic winds move down the gradient of the ice surface and are funneled through coastal valleys to produce powerful blizzards lasting for days at a time.
Still other types of local winds, bearing such names as foehn and Chinook, result when strong regional winds passing over a mountain range are forced on descend on the lee side with the result that the air is heated and dried.
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