FIGURE2 Awind rose
The circles around the image represent the various percentages of occurrences of the winds. For example, the ray to the south reaches the 20% ring, meaning a frequency of 20% blowing from that direction.
N
NW
NE
The rays use colour to show wind speed.
W
E
Wind roses have the ray drawn towards the centre. In this figure, the longest ray is from the south-west, showing most wind is south-westerly. It is most frequent.
This wind rose shows data for eight points of the compass.
SE
SW
S
Calm
km per hour
0–10
10–20 20–30 30–40 over 40
8.13.2 Showme How to read a wind rose You will need: • a wind rose (see FIGURE3 ) • a ruler. Procedure To describe wind patterns using a wind rose, you need to examine the rays’ direction, length and width. Wewill use FIGURE3 to explore this process. Step1 Determine the direction of wind with the greatest frequency by ýnding the longest ray. In FIGURE3 , the longest ray is from the south, so we can say that the predominant average wind direction in Melbourne at 3 pm is a southerly. Step2 Determine the direction of wind with the highest speed by ýnding the widest ray. In FIGURE3 , we can see that the highest average speeds were reached by winds coming from the north (northerlies). Step3 Work out the general pattern and main features of wind direction and strength. The FIGURE3 wind rose shows us that in Melbourne at 3 pm, the predominant average winds are southerlies, occurring more than 30 per cent of the time. The next most frequent wind at 3 pm is a northerly, which blows more than 20 per cent of the time. Winds blow from the west only around 10 per cent of the time, and easterlies are very infrequent.
Jacaranda Humanities Alive 7 Victorian Curriculum Third Edition
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