Weather elements

 Wind direction and speed

How to calculate wind direction and speed 

Wind is moving air and it is described by the compass direction from where it is blowing, for example north, south-east etc.

Figure 1.1 A wind vane

Figure 1.2 Windsock

A wind vane (see Figure 1.1) can be used to determine the wind direction. At airports or on runways a windsock is used (see Figure 1.2). You can also determine wind direction by looking at flags or at smoke coming from a fire.

The wind vane is normally made of metal and you will find it on a high building or on top of a long pole. The wind vane must be in an area where there is free flow of wind.

Wind will push against the largest surface of the arrow (the tail) until the arrow swings around to be parallel with the windand offers no resistance any more. The arrow head will therefore always point in the direction from where the wind is coming.

As well as wind direction,  it is also important to measure wind speed. This is measured with an anemometer (see Figure 1.3). The unit in which wind speed is measured is knots, km/h (kilometers per hour) or m/s ( meters per second). One knot equals 1.85 km/h.

Figure 1.3  Cup anemometer 

The cup anemometer consists of round rotating cups, facing in different directions. The wind blows into the cups and sets them spinning. The speed at which the cups are rotating is read from a dail. Anemometers can be held in the hand or mounted on a long pole.