Wind speed describes how fast the air is moving past a certain point. This may be an averaged over a given unit of time, such as miles per hour, or an instantaneous speed, which is reported as a peak wind speed, wind gust or squall.
Wind direction describes the direction on a compass from which the wind emanates, for instance, from the North or from the West.
Influencing Factors
Wind direction and speed are caused by differences in air temperature and variations in barometric pressure. Wind moves from areas of high air pressure to low air pressure. The larger the difference in pressure, the faster the wind will move. Land forms and topography also influence wind speed and direction. Large bodies of water, such as the Great Lakes and oceans, promote high wind speeds.
Importance
Wind speed and direction are important for monitoring and predicting weather patterns and global climate. Wind speed and direction have numerous impacts on surface water. These parameters affect rates of evaporation, mixing of surface waters, and the development of seiches and storm surges. Each of these processes has dramatic effects on water quality and water level.
Measurement
Wind speed is typically reported in miles per hour, knots, or meters per second. One mile per hour is equal to 0.45 meters per second and 0.87 knots. The measurement of wind speed is usually done using a cup or propeller anemometer, which is an instrument with three cups or propellers on a vertical axis. The force of the wind causes the cups or propellers to spin. The spinning rate is proportional to the wind speed.
Wind direction is typically reported in degrees and describes the direction from which the wind emanates. A direction of 0 degrees means the wind is coming from North on a compass, and 180 degrees is due South. A direction of 270 degrees would indicate a wind blowing in from the west. Wind direction is measured by a wind vane that aligns itself with the direction of the wind.