In this post we show how to produce a simple wind rose using Microsoft Excel or Open Office Calc. Two sample files are also available.
A wind rose is a chart which gives a view of how wind speed and wind direction are distributed at a particular location over a specific period of time. It is a very useful representation because a large quantity of data can be summarised in a single plot.
The first step to plot a wind rose with an electronic data sheet is to organise the wind data in a table according to their direction and speed classes. In other words the joint distribution of wind direction and speed must be calculated, as shown for example in the next figure. Each yellow cell contains the number of events observed over a specific time period for a specific combination of wind direction and speed. For example, wind blowing from North (N) with a speed smaller than 1 m/s has been observed 51 times, while wind blowing from North East (NE) with speed between 1 m/s and 2 m/s has been observed 159 times. If available, the user may also specify the average wind speed for each direction, as shown for example in the green cells. The total number of events and the corresponding percentages for each direction and wind speed class are automatically updated.
The example file uses 16 directions and 6 wind speed classes, but their number and contents can be easily modified.
Once the number of observations for each direction and wind speed class has been specified for each yellow cell, three charts are produced: the wind rose, the wind direction distribution and the wind speed distribution. If the average wind speed for each direction is also specified, then a fourth chart is produced representing the rose of the average wind. Examples of these four charts are reported in the following images.
The joint distribution of wind direction and speed must be determined by the user. This task might require long times, particularly for large time series of data. In a wind rose the length of each arm is proportional to the number of events, or the frequency, at which wind was observed from that direction. For a specific direction, the different wind speed frequencies sum up to give the total length of the arm. The wind rose plotted with the Microsoft Excel or Open Office Calc files does have such feature. If you need more professional wind roses and more complex analysis of your data, you might want to evaluate WindRose PRO.
METAR wind roses for year 2011.