Prevailing winds

PREVAILING WINDS

Prevailing winds are winds that blow predominantly from a single general direction over a particular point on the Earth's surface. The dominant winds are the trends in direction of wind with the highest speed over a particular point on the Earth's surface. A region's prevailing and dominant winds are enacted by global patterns of movement in the Earth's atmosphere.[1] In general, easterly flow occurs at low and medium latitudes globally. In the mid-latitudes, westerly winds are the rule and their strength is largely determined by the polar cyclone. In areas where winds tend to be light, the sea breeze/land breeze cycle is the most important to the prevailing wind; in areas which have variable terrain, mountain and valley breezes dominate the wind pattern. Highly elevated surfaces can induce a thermal low, which then augments the environmental wind flow.

Wind roses are tools used to determine the direction of the prevailing wind. Knowledge of the prevailing wind allows the development of prevention strategies for wind erosion of agricultural land, such as across the Great Plains. Sand dunes can orient themselves perpendicular to the prevailing wind regime within coastal and desert locations. Insects drift along with the prevailing wind, while birds are able to fly more independently of it. Prevailing winds in mountain locations can lead to significant rainfall gradients within the topography, ranging from wet across windward-facing slopes to desert-like conditions along their lee slopes. Prevailing winds can have differences due to the uneven heating of the Earth.

Effect on precipitation

Orographic precipitation

Main articles: Orographic lift, Precipitation types (meteorology), and United States rainfall climatology

Orographic precipitation occurs on the windward side of mountains and is caused by the rising air motion of a large-scale flow of moist air across the mountain ridge, resulting in adiabatic cooling and condensation. In mountainous parts of the world subjected to consistent winds (for example, the trade winds), a more moist climate usually prevails on the windward side of a mountain than on the leeward or downwind side. Moisture is removed by orographic lift, leaving drier air (see katabatic wind) on the descending and generally warming, leeward side where a rain shadow is observed.

In South America, the Andes mountain range blocks Pacific moisture that arrives in that continent, resulting in a desertlike climate just downwind across western Argentina.[25] The Sierra Nevada range creates the same effect in North America forming the Great Basin and Mojave Deserts.

Effect on nature

Sand blowing off a crest in the Kelso Dunes of the Mojave Desert, California.

See also: Dune, Erosion, and Insect

Insects are swept along by the prevailing winds, while birds follow their own course.[28] As such, fine line patterns within weather radar imagery, associated with converging winds, are dominated by insect returns.[29] In the Great Plains, wind erosion of agricultural land is a significant problem, and is mainly driven by the prevailing wind. Because of this, wind barrier strips have been developed to minimize this type of erosion. The strips can be in the form of soil ridges, crop strips, crops rows, or trees which act as wind breaks. They are oriented perpendicular to the wind in order to be most effective.[30] In regions with minimal vegetation, such as coastal and desert areas, transverse sand dunes orient themselves perpendicular to the prevailing wind direction, while longitudinal dunes orient themselves parallel to the prevailing winds.