WEATHER AND CLIMATE

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WEATHER AND CLIMATE
Temperature
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Elements of Weather Temperature

• Temperature refers to the degree of hotness or
  coldness of the air
• It varies throughout the day in a place
• The temperature rises and falls as the Earth
  rotates from west to east and it rises during the
  day and falls at night
• It also varies from place to place
• Temperature gets cooler as we go to higher
  grounds
• Places nearer the Equator are warmer throughout
  the year than places farther away from it

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Elements of Weather Temperature
What is the reason for Singapores hot climate?
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Factors Affecting Temperature

• Due to angle of incidence, the suns ray travels
  a shorter distance through the atmosphere and the
  solar radiation is concentrated on a smaller area
• These places experience uniform temperatures
  annually due to the tilt of the earth on its
  axis and cause these places to face the sun and
  receive the same radiation all year round.

1. Latitude
Places at lower latitudes are always hotter than
those at higher latitudes
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Factors Affecting Temperature

• 2. Altitude
• Temperature falls as altitude increases at a rate
  of 6.5C/1000m (known as the Normal lapse rate)
• Air is less dense at higher altitudes -gt absorb
  less long wave radiation -gt lower temperatures

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Measuring Temperature

• Air temperature is measured with a thermometer
• The scale is in degree Celsius (OC)
• Daily maximum temperature refers to the highest
  temperature reading for the day
• Daily minimum temperature refers to the lowest
  temperature reading for the day

Glass tube
Mercury or alcohol
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Measuring Temperature

• Maximum temperature is measured by the maximum
  thermometer
• It consists of a glass tube containing mercury
  and a metal index
• When temperature rises, the mercury expands and
  pushes the metal index upwards
• When temperature falls and the mercury contracts,
  the metal index stays in place

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Measuring Temperature

• The minimum thermometer works in the same way to
  measure the lowest temperature reading, but
  contains alcohol instead of mercury
• The maximum and minimum thermometer, which is
  also called the U-shaped thermometer, can
  measure both maximum and minimum temperatures

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Sixs Thermometer
Sixs Thermometer/U-shaped thermometer
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Sixs Thermometer

• When temp increases,
• both alcohol and mercury expand
• alcohol in the left limb forces the mercury
  towards the right limb
• the mercury pushes the index up in the right limb
• part of the alcohol in the right limb vaporises
  and moves into the vacuum
• end of the index closest to the mercury gives the
  maximum temperature

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Sixs Thermometer

• When temp decreases,
• both alcohol and mercury contract
• alcohol vapour in the right bulb liquifies so
  that the mercury now flows in the opposite
  direction and pushes the up the metal index in
  the left limb
• end of the index closest to the mercury gives the
  minimum temperature

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Calculating Temperatures

• Diurnal temperature range
• Average temperature range
• Mean monthly temperature
• Annual range of temperature
• Mean annual temperature

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Calculating Temperatures

• The mean daily temperature is the average
  temperature of a place on any one day

• The daily temperature range is the difference
  between the maximum and minimum temperatures
  recorded in a day

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Calculating Temperatures

• The mean monthly temperature is the average
  temperature of a place in a month

• The mean annual temperature is the average
  temperature in a place within a year

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Calculating Temperatures

• The annual temperature range is the difference
  between the maximum and minimum mean monthly
  temperatures recorded in a year

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Elements of Weather Temperature
Isotherms lines joining places of equal
temperature
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Elements of Weather Temperature
Line graph
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Stevenson Screen

• Instruments used to measure temperature are
  usually placed in a Stevenson Screen
• Maximum and minimum thermometers or sixs
  thermometer and a wet and dry bulb thermometer
  are kept in the SS.
• Barometer can also be kept in SS

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Stevenson Screen

• It is made of wood
• wood is a poor conductor of heat
• It is painted white
• white paint reflects light so that the box does
  not heat up excessively
• Its is a raised 1.2 metres above ground
• to minimise the effect heat radiating from the
  ground

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Stevenson Screen

• The sides and doors have louvres
• to allow free air movement in and out of the
  boxdirect heat of the Sun
• It has a double-layered roof with intervening air
  space
• to reduce excessive heating inside the box as air
  is a good insulator
• Where should a stevenson screen be sited?

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