WEATHER STUDIES
 Weather is the state of the atmosphere at a given place at a given time.
 Weather is dynamic meaning that it changes.
Why study weather
 To be able to predict future weather conditions
 To prepare in case of any weather hazards
 To be able to know what type of crops to plant to our area
Jobs linked to weather studies
 Meteorologist
 Pilots
 farmers
Elements of weather
 There are 7 elements of weather namely:
 Rainfall; temperature; humidity; cloud cover ; wind speed and direction; sunshine;
atmospheric pressure
 Table below shows elements of weather, instrument used to measure it and the units.
TASK 1
Copy and complete the table below.
Weather Element
Rainfall
Instrument of measurement
Rain gauge
unit
Millimeters (mm)
TEMPERATURE
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Is the degree of either hot or cold
A six’s thermometer is used to measure temperature
It is u-shaped instrument, made of glass and is made up of the minimum and maximum
thermometer.
Maximum thermometer is located on right side and minimum thermometer is on the left
side
Minimum thermometer contains alcohol and it measures lowest temperature of the day,
whilst maximum temperature contains mercury and it measures highest temperature of
the day.
In order to get an accurate reading, this instrument is kept in the Stevenson screen and
readings must be read at eye level at the lower end of the index
THE SIX’S THERMOMETER
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Temperature calculations
Temperature recordings are used to calculate various statistics which include :
i.
Daily temperature range- it is the difference between maximum and minimum
temperature for one day
 Mean daily temperature = maximum temperature – minimum
temperature.
25 Oc-18 Oc=7 OC
ii.
iii.
iv.
Daily average temperature - It is also referred to as mean daily temperature
 Maximum temperature +minimum temperature
2
25 Oc + 18 Oc = 21.5 OC
2
Mean monthly temperature =
total daily mean temperature
Number of days in that month
Yearly temperature range = highest mean monthly temperature – lowest mean
temperature
TASK 2
Copy table and complete the temperature calculations
MAXIMUM
TEMPERATURE OC
MINIMUM
TEMPERATURE OC
DAILY RANGE
TEMPERATURE OC
DAILY MEAN
TEMPERATURE OC
36
12
3
27
8
23
-5
-9
11
-12
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NB: isotherms are lines on a map showing places of equal temperature.
HUMIDITY
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Refers to the amount of moisture in the atmosphere.
It is measured using a hygrometer.
Relative humidity (RH) of the air is expressed as a percentage.
It is the amount of water vapour the air can hold at a given temperature.
The hygrometer is made up of two thermometers namely the wet and dry bulb
thermometers
Hygrometer( traditional instrument)
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The wet bulb thermometer has got a muslin cloth wrapping its bulb and the
cloth is dipped in distilled water.
When Rh is 100%, it means the air is saturated.
When the air is cooled, it will reach a temperature referred to as due point
temperature- which is the maximum temperature at which water vapour can be
held any further.
Difference between the wet and dry bulb readings will give us what is known as
depression.
When difference is high it means air dry
When difference is zero it means the air is saturated.
When difference is low it means air is humid
Humidity table
Wind
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Wind is air moving over the earth’s surface.
Its velocity is measured using a cup anemometer
Its units are km/hr or knots.
Knots are represented using symbols on a beufort scale.
Cup anemometer
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Wind gets its characteristics from where it is coming from.
The source region is where the wind originates.
Wind has the following characteristics
a) Warm and moist
b) Warm and dry
c) Cool and moist
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d) Cool and dry
Wind’s characteristics are modified/change by surfaces over which it blows over.
A wind vane is used to measure wind-direction.
The arrow points to the direction from which the wind is blowing from.
For an example, an easterly wind blows from the east whilst a westerly wind blows
from the west.\
NB: both wind vane and cup anemometer must be placed at the top most part of
buildings for them to give a reliable wind record.
Atmospheric pressure
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Pressure is force exerted on every object.
Atmosphere has weight which varies from place to place and from time to time.
Average pressure at sea level is 1013 mb
Isolines on a map showing places of equal pressure are called isobars.
A barometer is used to measure atmospheric pressure.
There are two types of barometers namely mercury and aneroid barometer