<P> 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 . 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 . </P> <P> 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 . </P> <P> A wind rose is a graphic tool used by meteorologists to give a succinct view of how wind speed and direction are typically distributed at a particular location . Presented in a polar coordinate grid, the wind rose shows the frequency of winds blowing from particular directions . The length of each spoke around the circle is related to the frequency that the wind blows from a particular direction per unit time . Each concentric circle represents a different frequency, emanating from zero at the center to increasing frequencies at the outer circles . A wind rose plot may contain additional information, in that each spoke is broken down into color - coded bands that show wind direction ranges . Wind roses typically use 8 or 16 cardinal directions, such as north (N), NNE, NE, etc., although they may be subdivided into as many as 32 directions . </P> <P> The trade winds (also called trades) are the prevailing pattern of easterly surface winds found in the tropics near the Earth's equator, equatorward of the subtropical ridge . These winds blow predominantly from the northeast in the Northern Hemisphere and from the southeast in the Southern Hemisphere . The trade winds act as the steering flow for tropical cyclones that form over world's oceans, guiding their path westward . Trade winds also steer African dust westward across the Atlantic Ocean into the Caribbean sea, as well as portions of southeast North America . </P>

What are the major global wind systems on earth