WIND ROSE

Wind Rose diagram provides a graphical summary of the frequency distribution of wind direction and wind speed over an extended period of time. The following procedure is followed to develop a wind rose from hourly observations.

Step I: Analysis for Wind Direction

Group all winds of a given direction together using the table given below: 

All Winds From
Direction
0o
Calm
348.75o - 11.25o
N
11.25o - 33.75o
NNE
33.75o - 56.25o
NE
56.25o - 78.75o
ENE
78.75o - 101.25o
E
101.25o - 123.75o
ESE
123.75o - 146.25o
SE
146.25o - 168.75o
SSE
168.75o - 191.25o
S
191.25o - 213.75o
SSW
213.75o - 236.25o
SW
236.25o - 258.75o
WSW
258.75o - 281.15o
W
281.15o - 303.75o
WNW
303.75o - 326.25o
NW
326.25o - 348.75o
NNW
Step II: Determination of Frequency of Wind in Wind Direction

Find the number of readings in each directional category and the total number of readings. Then find the percentage that each of the 16 wind directions occurs.

Step III: Analysis for Wind Speed

    For each wind direction, group the readings into wind speed categories. For example, use ranges of 3 miles/hour , i.e. calm, 1-3 mph, 4-6 mph, 7-10 mph etc.

    For each wind direction, find the percentage of readings in each speed range.

Step IV: Preparation of Polar Diagram

    On polar coordinate paper, label each of the 16 wind directions

    Plot each wind direction percentage from Step II making the length of each line proportional to its corresponding percentage.

    For each wind direction line plotted, divide into wind speed categories using the percentages calculated in Step III (2). Put the lowest         speed category (i.e. 1-3 mph) closest to the center of the graph, or,

    Put the percentage of calm winds (i.e. 0 mph) in the center circle of the graph.

Step V: Determination of Mean Wind Speed

    For each wind direction, find the mean wind speed

    Plot each mean wind speed adjacent to the line plotted in Step IV(2) using an appropriate scale.

Click here to see the polar diagram.

Problem:

Draw a wind rose showing both directional frequencies and wind speed frequencies from 3 hourly observations for a one week period for Toledo airport given in the following table.

The observations were taken in December 1982 and are obtained from Local Climatological Data sheet for Toledo.

DAY
HOUR L.S.T.
WIND
DIRECTION
WIND
SPEED (KNOTS)
1 01 
04 
07 
10 
13 
16 
19 
22		 18 
17 
16 
17 
23 
18 
15 
16		 6 
5 
5 
6 
7 
6 
7 
7
2 01 
04 
07 
10 
13 
16 
19 
22		 18 
15 
14 
18 
17 
16 
16 
18		 6 
7 
7 
10 
9 
10 
10 
10
3 01 
04 
07 
10 
13 
16 
19 
22		 18 
17 
23 
21 
20 
21 
27 
16		 11 
13 
14 
8 
13 
13 
7 
10
4 01 
04 
07 
10 
13 
16 
19 
22		 33 
27 
28 
34 
04 
06 
09 
08		 14 
4 
6 
5 
3 
6 
9 
10
5 01 
04 
07 
10 
13 
16 
19 
22		 07 
07 
10 
15 
15 
18 
23 
21		 7 
10 
6 
10 
13 
12 
15 
15
6 01 
04 
07 
10 
13 
16 
19 
22		 21 
22 
28 
29 
31 
29 
26 
24		 16 
13 
17 
12 
16 
11 
8 
6
7 01 
04 
07 
10 
13 
16 
19 
22		 24 
23 
24 
23 
25 
25 
36 
04		 7 
8 
7 
7 
9 
8 
3 
6
 
 

Note:
WIND DIRECTION: DIRECTIONS ARE THOSE FROM WHICH THE WIND BLOWS, INDICATED IN TENS OF DEGREES FROM TRUE NORTH: I.E., 09 FOR EAST, 18 FOR SOUTH, 27 FOR WEST. AN ENTRY OF 00 INDICATES CALM.
MPH = KNOTS x 1.151