Creating a Wind Rose
In this exercise, students will use given wind data to create a wind rose.
A wind rose is a graph showing the direction, speed, and frequency of wind in a particular area. To make a wind rose, a compass is divided into 8, 12, or 16 sectors. The wind direction data is then analyzed to determine what percent of the time the wind blows from each direction. The data is then represented on a circular graph as a line eminating from the center of the circle whose length is scaled to the percentage obtained from the data, pointing in the given direction (for example, if the wind was blowing to the north twenty percent of the time you would draw a line north that would reach to the 20% line). The resulting plot resemebles a rose.
To include wind speed, the percent of time that the wind is blowing at given speeds toward each direction needs to be determined (for example, the percent of time the wind was blowing to the north at 1-4 m/s, 4-8 m/s, 8-12 m/s, and over 12 m/s). This data is then plotted as scaled blocks on the line showing wind direction. For an example of a 16 sector wind rose click here.
For examples, and to learn more about wind roses, use the links below.
In this activity students will create a wind rose using given data for each of four months (Jan, Apr, Aug and Oct -- one month in each season)of the year 2000 using only wind direction (ie, not wind speed) at the MERI weather station. We will be using eight sectors in this activity (N, NE, E, SE, S, SW, W, NW). Wind direction data from four different months in 2000 has already been compiled into a spreadsheet for your use; it also contains the frequency data and a sample plot. Click to download Excel file with data for four months.
Frequency data (ie, the percent of time the wind blows from each direction) can be compiled by hand (quite tedious) or using Excel (but to make a frequency chart in Excel, you must use an advanced "IF " function to categorize a single wind direction given in degrees into one of the 8 wind direction categories. see instructions below). The wind rose can be plotted on paper or using a "radar" chart type in Excel. For a blank wind rose to print for making the wind rose on paper, click here.
To compile the data so you can make a windrose, you need to make a frequency data table like this:
|Direction for Tally||Frequency||Percentage|
1. Did the average wind direction change from season to season? Why might this be?
2. Why would knowing the average wind direction and speed be important?
Instructions for making a frequency table in Excel
To make a frequency chart for other months, you must use a slightly advanced "IF " function to categorize a single wind direction given in degrees (0 = north, 90 = east, 180 = south, 270 = west) into one of the 8 wind direction categories (N, NE, E, etc.)
Before you can make a count using an IF statement, nine columns must be created for each of the compass directions, with North being represented twice. In the first North column, in the cell corresponding with the first direction data, type in this IF statement without the quotes "=IF(X<=22.5,1,0)", where X in this statement represents the cell in which the direction data came, called a reference cell (ie. B3 or B2). This IF statement tells the computer to check the cell with the direction in it, and if the number is less than or equal to 22.5, then a "1" will be placed in the cell, if not, a "0" is placed in the cell. Now, copy that if statement, and paste a copy down to the last wind direction data (when pasting, the reference cell automatically changes to correspond with the correct data point). Next, this same process needs to be performed for the other directions. The IF statements to be used are as follows:
NE: "=IF(B3>22.5,IF(B3<=67.5,1,0),0)" searches
for data between 22.5 and 67.5
E: "=IF(B3>67.5,IF(B3<=112.5,1,0),0)" searches for data between 67.5 and 112.5
SE: "=IF(B3>112.5,IF(B3<=157.5,1,0),0)" searches for data between 112.5 and 157.5
S: "=IF(B3>157.5,IF(B3<=202.5,1,0),0)" searches for data between 157.5 and 202.5
SW: "=IF(B3>202.5,IF(B3<=247.5,1,0),0)" searches for data between 202.5 and 247.5
W: "=IF(B3>247.5,IF(B3<=292.5,1,0),0)" searches for data between 247.5 and 292.5
NW: "=IF(B3>292.5,IF(B3<=337.5,1,0),0)" searches for data between 292.5 and 337.5
N: "=IF(B3>337.5,1,0)" searches for data above 337.5
When the columns have all been completed, the sum of each of the columns should be determined and recorded. Remember to add the two North columns together. The frequency of each direction, along with the total of all directions, should be determined also. Now, determine and record the percentages of each direction, and you are finished.