The paths taken by these pressure systems is closely correlated to upper-level air flow and the polar jet stream . The average position of the polar jet stream, and hence the paths of cyclonic systems, migrates equatorward with the approach of winter and poleward as summer nears. El Ni o is the name given to the periodic warming of the ocean that occurs in the central and eastern Pacific. It is associated with periods when a weakened pressure gradient causes the trade winds to diminish. A major El Ni o event triggers extreme weather in many parts of the world.
Local winds are small-scale winds produced by a locally generated pressure gradient.
The two basic wind measurements are direction and speed . Winds are always labeled by the direction from which they blow . Wind speed is measured using a cup anemometer . The instrument most commonly used to measure wind direction is the wind vane . When the wind consistently blows more often from one direction than from any other, it is termed a prevailing wind .