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

Elements of Weather: Temperature

Singapore What is the reason for

Singapore’s hot climate?

Elements of Weather: Temperature

Factors Affecting Temperature

1. Latitude

• Due to angle of incidence, the sun’s 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.

Places at lower latitudes are always hotter than those at higher latitudes

Factors Affecting Temperature

2. Altitude

• Temperature falls as altitude increases at a rate of 6.5°C/1000m (known as the Normal lapse rate)

• Air is less dense at higher altitudes -> absorb less long wave radiation -> lower temperatures

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

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

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

Six’s Thermometer

Six’s Thermometer/U-shaped thermometer

left bulb right bulb

metal index

vacuum

alcohol

mercury

right bulb

Six’s 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

Six’s 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

• Diurnal temperature range

• Average temperature range

• Mean monthly temperature

• Annual range of temperature

• Mean annual temperature

Calculating Temperatures

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

FormulaMean daily

temperature =

Daily maximum Daily minimum temperature + temperature

2

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

Formula Daily temperature range =

Daily maximum Daily minimum temperature - temperature

Calculating Temperatures

Calculating Temperatures

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

FormulaMean monthly

temperature =

Sum of mean daily temperatures for the month

Number of days in the month

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

FormulaMean annual

temperature =Sum of mean monthly temperatures in the year

2

Calculating Temperatures

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

Formula Annual temperature range =

Maximum Minimum mean monthly - mean monthly temperature temperature

Elements of Weather: Temperature

Isotherms: lines joining places of equal temperature

Elements of Weather: Temperature

Line graph:

Stevenson Screen

Instruments used to measure temperature are usually placed in a Stevenson Screen

Maximum and minimum thermometers or six’s thermometer and a wet and dry bulb thermometer are kept in the SS.

Barometer can also be kept in SS

Stevenson ScreenIt 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

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?