EXPERIMENT 1 :

PLOTTING WIND ROSE DIAGRAM

1.0 OBJECTIVES

- To observe meteorological data of wind speed and wind direction of a specific location.

- To plot the information about the distribution of wind speeds and the frequency of the

varying wind directions through wind rose diagram.

2.0 INTRODUCTION

A wind rose is a graphic tool used by meteorologists to give a succinct view of

how wind speed and direction are typically distributed at a particular location. Historically,

wind roses were predecessors of the compass rose (found on maps), as there was no

differentiation between a cardinal and the wind which blew from such a direction. Using

a polar coordinate system of gridding, the frequency of winds over a long time period are

plotted by wind direction, with color bands showing wind ranges. The directions of the rose

with the longest spoke show the wind direction with the greatest frequency.

Presented in a circular format, the modern wind rose shows the frequency of winds blowing 

from  particular directions over a thirty year period. The length of each "spoke" around the

circle is related to the frequency that the wind blows from a particular direction per unit time.

Each concentric circle represents a different frequency, emanating from zero at the center to

increasing frequencies at the outer circles. A wind rose plot may contain additional

information, in that each spoke is broken down into color-coded bands that show wind speed

ranges. Wind roses typically use 16 cardinal directions, such as north (N), NNE, NE, etc.,

although they may be subdivided into as many as 32 directions. In terms of angle

measurement in degrees, North corresponds to 0°/360°, East to 90°, South to 180° and West

to 270°.

Compiling a wind rose is one of the preliminary steps taken in constructing airport runways,

as aircraft perform their best take-offs and landings pointing into the wind. The wind rose is

the time honored method of graphically presenting the wind conditions, direction and speed,

over a period of time at a specific location. To create a wind rose, average wind direction and

wind speed values are logged at a site, at short intervals, over a period of time,1 week, 1

month, or longer. The collected wind data is then sorted by wind direction so that the

percentage of time that the wind was blowing from each direction can be determined.

Typically the wind direction data is sorted into twelve equal arc segments, 30° each segment,

in preparation for plotting a circular graph in which the radius of each of the twelve segments

represents the percentage of time that the wind blew from each of the twelve 30° direction

segments. Wind speed data can be superimposed on each direction segment to indicate, for

example, the average wind speed when the wind was blowing from that segment's direction

and the maximum wind speed during the logging period.

Normally, the wind rose is extremely useful for sitting wind turbines .The best way of

measuring wind speeds at a prospective wind turbine site is to fit an anemometer to the top

of a mast which has the same height as the expected hub height of the wind turbine to be

used . In this way , one can avoids the uncertainty involved in recalculating the wind speeds

to a different height .

Example wind rose diagram :

3.0 MATERIALS & APPARATUS

i. Watchdog 2000 Series Weather Station

The stations are completely weatherproof and feature 12-bit resolution for higher accuracy.

The stations can be accessed at different times by multiple users because the data is not

cleared from memory following a download. The 2000-Series Weather Stations can

communicate via direct-wire, radio or telephone connections. Current weather conditions,

historical data, and computed parameters are easily viewed on the station’s LCD screen.The

weather station should be located in an open, unobstructed, grassy area to ensure accurate

measurement of wind, rainfall, sunlight, and evapotranspiration. Mounting hardware is

provided to attach the weather station to a 4” X 4” treated wooden post or to a mast or pole

up to 1.25 inches in diameter. The mounting pole should be securely anchored perpendicular

to the ground. It also can be used with mounting tripod (as in Figure 1). The data on both

wind speeds and wind directions from the anemometer are collected on electronic chips and

can be modified with Spec Ware software.

Figure 1: Weather Station mounted on tripod

ii. Anemometer

The anemometer arm is attached to the enclosure back plate with two clamps. After

positioning the arm, the screws should be tightened to secure it in place. Push the wind cups

onto the bottom of the shaft flush with the bottom of the assembly and tighten the set screw.

When released, the cups should drop slightly. If the cups do not spin freely, loosen the set

screw and lower the cups slightly. The gap between cup hub and assembly should be about

1/16 inch. Push the wind vane onto the top of the shaft and calibrate (see Calibrating the

Anemometer p. 23 for calibration procedure).The weather station should be located in an

open, unobstructed, grassy area to ensure accurate measurement of wind, rainfall, sunlight,

and evapotranspiration.

4.0 PROCEDURE

1. The WatchDog 2900ET Weather Station should be allocated in an open, without

obstructed, grassy area to ensure accurate measurement of wind speed and direction.

2. Setting the Time and Date:

i. Press DISPLAY and press SET. With the arrow keys ◄► to scroll to the Time

and Date.

ii. Press SET for date setting with [Month/Date/Year]. Use the arrow keys ◄► to

scroll. Next, set the time with [Hour: Minutes am/pm].

3. Setting the Interval:

i. Press SET and arrow keys ◄► to scroll to the Interval.

ii. Set the interval to 5 minutes

4. Setting North

i. Press SET and arrow keys ◄► to scroll to the SET NORTH.

ii. Press SET and move the arrow to the North and press SET once again.

iii. Pressing the DISPLAY key for bring the LCD display to life. Pressing another time

DISPLAY key for deactivate the LCD display but the data still will be recorded

even the display is not active.

iv. Get the reading of the Wind Speed and Wind Direction for every 5 minutes.

Safety precaution

Normal operation of the equipment in not considered hazardous. However, the

RECOMMENDED PROCEDURES SHOULD BE FOLLOWED to be sure that the

instruction is performed under safe conditions.

BE ALERT ALWAYS to the procedures which may be a hazard to the operator or be

injurious to the equipment. Every control device and switch has a specific operational

application.

5.0 RESULTS

TIME ( am )

(5 min logging interval)WIND DIRECTION WIND SPEED

1 10.00 0 0

2 10.05 1 0

3 10.10 12 2

4 10.15 100 8

5 10.20 125 2

6 10.25 70 7

7 10.30 80 6

8 10.35 240 2

9 10.40 240 3

10 10.45 240 4

11 10.50 170 8

12 10.55 300 8

13 11.00 280 8

14 11.05 180 9

15 11.10 360 7

16 11.15 156 12

17 11.20 286 10

18 11.25 272 6

19 11.30 16 4

20 11.35 30 3

21 11.40 120 11

22 11.45 360 4

23 11.50 220 12

24 11.55 360 7

Direction0°-

45°

46°-

90°

91°-

135°

136°-

180°

181°-

225°

226°-

270°

271°-

315°

316°-

360°Total

N NE E SE S SW W NW

0

1

12

16

30

70

80

100

125

120

170

180

156

220 240

240

240

300

280

286

272

360

360

360

Frequency 5 2 3 3 1 3 4 3 24

Percentage

of Wind

Frequency

20.8 8.3 12.5 12.5 4.2 12.5 16.7 12.5 100%

No. of sector

Wind frequency = × 100 %

total of sector

NW NE

W E

SW SE

S

N

6.0 DISCUSSION

Wind roses can be used to graphically depict the predominant transport direction of

an area's winds. Wind rose statistics may not always be representative of true transport for

an area due to local terrain influences, coastal effects, exposure of the instruments, and

temporal variability of the wind.

Based on the result, it shows that the wind direction and wind speed is changing

parallel with the change of time. To create the wind rose diagram, the wind frequency must to

be calculated. The wind frequency can be calculated by using formula which is by dividing

the no. of sector with total of sector and multiply with 100 (in percentage).

From the wind rose diagram, the most of the wind frequency is located in the highest

degrees of the sectors, starting from 46o to 316o. From that, the direction of the wind can be

determined, where its shows that the wind occasionally blows in the east, south, and west

compared to the north.

7.0 CONCLUSION

Air quality is often correlated with the dominant transport direction of the wind. Wind

roses provide the best information regarding the percentage of time the direction(s) and

speed(s) associated with a certain air quality can be expected over a long period of time. By

comparing wind roses to trajectories of an assessment of how frequently that particular

trajectory could be expected over a period of time. Wind roses typically use 16 cardinal

directions, such as north (N), NNE, NE, etc., although they may be subdivided into as many

as 32 directions. In terms of angle measurement in degrees, North corresponds to 0°/360°,

East to 90°, South to 180° and West to 270°.

8.0 QUESTIONS

1. Define the prevailing wind direction

Prevailing wind direction is the wind direction that has been observed most frequently

during a given period, which is most often stated in day, month, season and year. It

should be the wind that blows predominantly from a single general direction.

2. Define the wind frequency

The wind frequency is the percentage of the time the wind is coming from a particular

direction, and should be obtained from the nearest weather station.

3. From your observation, what may govern the most common winds retrieved in

your experiment?

Elevation of place (obstacle of wind direction) and weather influences the most common

winds retrieved in our experiment.

4. From your observation, what may govern the most common winds retrieved in

your experiment?

From our observation, we found that, the result of our experiment, which are wind speed

and wind direction, govern dominantly by the availability of the wind. Since the place for

our experiment is surrounded by buildings, hence there is lacked of wind as the buildings

blocked off the wind that should be passed through the device and being taking down the

speed and direction. As a result, in our record, the wind speed and direction are not

changing much from time to time. Besides that, the weather of the day can govern the

wind too. As the day we having our experiment is not a windy day. Hence, the device can

hardly record any wind speed and direction from time to time.

Trade wind. The air at doldrums rises high over earth, recirculates poleward, and sinks

back toward the earth’s surface in the region of horse latitudes, and converge near

surface to the doldrums. Surface air from the horse latitudes that moves back toward the

equator and is deflected by the Coriolis Force, causing the winds to blow from the NE in

the Northern Hemisphere and from SE in the Southern Hemisphere is called trade winds.

It means that in both hemispheres, they tend to blow from the east to the west and

towards the equator. Sometimes the trade winds will just be called "easterly" to avoid

having to specify the hemisphere. These steady winds are called trade winds because

they provided trade ships with an ocean route to the New World.

9.0 REFERENCES

- http://www.novalynx.com/reference-wind-rose.html

- http://www.originlab.com/forum/topic.asp?TOPIC_ID=7623

- http://www.warensortiment.de/bedienung/ba-wetterstation-watchdog-eng.pdf

- http://en.wikipedia.org/wiki/Prevailing_winds