The Wind Across Australia Wind is the motion of air relative to the surface of the Earth. It is one of the most highly variable climatic elements, both in speed and direction. For this reason it is often studied by means of frequency analyses, provided here in the form of wind roses, rather than as averages. Information about maximum wind gusts is provided in the Tables of Climatic Averages. The general wind patterns are defined by the atmospheric pressure distribution, but locally the wind can be strongly affected by several factors, including: The time of day (e.g. sea breezes) Height above the ground The surrounding terrain For this reason care should be taken when interpreting any wind data. Specifying the Wind The wind direction is specified relative to true (geographic) north, and is the direction from which the wind is blowing. The direction can be specified either as the number of degrees clockwise from true north, or as one of the 8 or 16 compass points. Within Australia wind speeds are generally presented in kilometres per hour. For nautical use the wind speed is measured in knots, while for some scientific applications units of metres per second are used. Convert between different wind speed units The Wind Frequency Analysis Wind roses summarise the occurrence of winds at a location, showing their strength, direction, and frequency. The percentage of calms is represented by the size of the centre circle. Each branch represents wind coming from that direction, with north to the top of the diagram. The branches are divided into segments of different thickness, which represent wind speed ranges from that direction. For example, the thinnest segment may represent winds between 1 and 10 km/h. The length of each branch segment is proportional to the percentage of winds in that speed range, blowing from that particular direction. Wind Maps for Australia The following maps present data from selected sites around Australia. For convenience they have been grouped according to the season of the year characteristic of temperate Australia. In the northern parts of Australia it is often more appropriate to refer to the "wet season" from October to April and the "dry season" for the rest of the year. A list of all the sites in Australia which measure wind speed and direction can be found under Climate Data Available from the Bureau. Additional data can be obtained by Contacting the Bureau .