This document defines key weather elements and how they are measured. It describes weather as short-term atmospheric conditions while climate refers to long-term averages. Common instruments are discussed like the six's thermometer for temperature inside a Stevenson screen, the rain gauge for rainfall, and the wind vane and wind rose for wind direction and patterns. Formulas are provided for calculating daily, monthly, and annual averages of temperature and rainfall from collected data. Proper siting of instruments is also outlined.

1. Unit 15: Weather Elements
Objectives
Differentiate between weather and climate.
Understand the use and siting of the weather
instruments.

2. Weather
• Weather
describes the
condition of the
atmosphere of a
place over a
short period of
time.
• Temperature, rai
nfall and wind
Climate
• Climate is the
average conditions
of the atmosphere
of a place over a
long period of time.
• Average
temperature and
average rainfall
pattern is used.

3. Is this weather or climate data?

4. Is this a weather or climate data?
Climatic maps are used to show information
such as distribution of temperature and rainfall
of a country, region or the world.

5. Thermometer
• Temperature refers to the degree of heat in
the air. It tells us how hot or cold the air is.
• A thermometer is used to measure
temperature in degree Celsius (◦C) or degree
Fahrenheit(◦F).
• Six’s Thermometer or the maximum and
minimum thermometer is used to record the
highest and lowest temperatures of a day.

6. Six’s thermometer

7. • Made up of Mercury and
Alcohol
• Mercury – Very high
boiling point
• Alcohol – Very low
freezing point
• Read off the base of the
Indices (Indicators)

8. Activity - Reading the Six’s
Max = 30 oC
Min = 5 oC
Mercury
Metal
Indices
Alcohol
Max = 20 oC
Min = 10 oC
Max = 7.5 oC
Min = -15 oC

9. Stevenson Screen
• The Six’s thermometers are placed in a
white, wooden box called a Stevenson Screen.
• White wooden box to reflect heat
• Louvred sides to allow air to flow freely
• Doubled layered roof to prevent direct heating
from the sun
• Stand on stilts to prevent heat from the
ground to be trapped

12. Calculating Temperatures (1/5)
Daily temperature Range
= Maximum Temp - Minimum Temp
For example
Max temp = 30 oC Min Temp = 10 oC
Daily temp range = 20 oC

13. Calculating Temperatures (2/5)
Mean (average) daily temperature
= Maximum Temp + Minimum Temp
2
For example
Max temp = 30◦C Min Temp = 10◦C
Average daily temp= (30+10)/2
= 20◦C

14. Calculating Temperatures (3/5)
Mean (average) monthly temperature
= Total average daily temp for the month
Number of days in the month

15. Calculating Temperatures (3/5)
Mean (average) monthly temperature
= Average max temp + Average min temp
2
Only used this when
average maximum and
average minimum
temperature are given.

16. Calculating Temperatures (4/5)
Mean (average) Annual temperature
= Total average monthly temp in a year
12

17. Calculating Temperatures (5/5)
Annual temperature range
= Highest mean - Lowest mean
monthly temp monthly temp

18. Location X
Month Jan Feb Mar Apr May Jun Jul Aug Sep Oct Nov Dec
Temp 23 22 20.5 16.5 14 10.5 10 11 12.5 14 17.5 21
Mean Annual Temperature
= Total of mean monthly temperature / 12
= (23 + 22 + 20.5 + 16.5 + 14 + 10.5 + 10 + 11 + 12.5 + 14 + 17.5 + 21 ) / 12
= (192.5) / 12
= 16.04 oC
Annual Temperature Range
= Highest Temperature – Lowest Temperature
= 23 – 10
= 13 oC

19. Location Y
Month Jan Feb Mar Apr May Jun Jul Aug Sep Oct Nov Dec
Temp 25.5 26 26.5 27 27.5 28 27.5 27 26.5 26.5 26 26
Mean Annual Temperature
= Total of mean monthly temperature / 12
= (25.5 + 26 + 26.5 + 27 + 27.5 + 28 + 27.5 + 27 + 26.5 + 26.5 + 26 + 26 ) / 12
= (321) / 12
= 26.75 oC
Annual Temperature Range
= Highest Temperature – Lowest Temperature
= 28 – 25.5
= 2.5 oC

20. • Average daily or mean daily temperature:
• Calculation of temperature data:
Temperature
Average daily or
mean daily temperature
Maximum temperature + Minimum temperature
2
=
Daily temperature range Maximum temperature - Minimum temperature=
Average monthly
temperature
Sum of average daily temperatures for the month
Number of days in the month
=
Average annual
temperature
Sum of average monthly temperatures in a year
12
=
• Daily temperature range
• Average monthly temperature
• Average annual temperature

21. •An instrument used to measure the amount of
rainfall
•Rain falls through a funnel and is collected in the
bottle
•Excess rain that overflows is collected in the
copper cylinder
•Amount of rain collected is poured into a
measuring cylinder, calibrated in millimeters
• Rain gauge:
Rainfall
outer cylinder funnel
glass
bottle
measuring
cylinder
copper
cylinder

22. •One-third of
the rain gauge
is sunk into the
ground to
prevent
toppling
•To be placed in
an area free of
obstructions
•Rain gauge:
Rainfall
copper
cylinder
funnel
glass bottleouter
cylinder

23. Calculating Rainfall (1/4)
Daily rainfall
= Sum of all rainfall readings in a day

24. Calculating Rainfall (2/4)
Monthly rainfall
= Sum of all daily rainfall readings in a
month

25. Calculating Rainfall (3/4)
Total annual rainfall
= Sum of the total monthly rainfall received for the year.

26. Calculating Rainfall (4/4)
Mean (average) monthly rainfall
= Total annual rainfall
12

27. • Horizontal movement of air from a high
pressure area to a low pressure area
• Associated with land and sea breezes
Wind
wind
high
pressure
low pressure
cold air sinkswarm air rises
land Sea

28. Wind
•In the day, air over the sea is cooler than that
over the land, thus the cooler air
sinks, creating a higher pressure area.
•Warmer air over the land rises, creating a low
pressure.
•Differences in pressure cause the air over the
sea to move towards the low pressure over the
land.
•This horizontal movement of air causes wind.
NOTE: Greater differences in pressure give rise
to stronger breezes.

29. •The wind vane
points to the
direction where
the wind is
blowing from
•It is made up of
a freely moving
pointer and four
cardinal points –
north, south, ea
st, west
• Measuring wind direction:
Wind vane

30. •The wind rose records the
wind direction.
•It is represented by a
centre circle and eight
arms representing the main
eight compass directions.
•The number of calm days is
recorded in the centre
circle.
•The longer the arms, the
more days the wind is
received from that
direction.
Wind rose
5 E
S
N
NW
SW
NE
number of calm days5

31. • Siting of weather
instruments:
Wind
Stevenson screen
• 120cm above ground level
• Six’s thermometer is kept inside
• insulated from heat by material
and design
rain gauge
• 30cm above ground level
• on short grass away in an open
field from buildings
wind vane
• top of the meteorological
station with no obstructions

32. 5 meteorological/weather stations in
Singapore