Elements of Weather & Climate

Temperature

Definition

Temperature is the degree of heat or cold in the atmosphere

It is measured in ºC or ºF

Warming of air

Air is warmed by means of: Convection: The process through which hot air,

being lighter than cold air, rises as a convection current

Conduction: The process through which the air receives heat from the ground it is in contact with

Radiation: The process through which the heat energy from the ground is sent back to space. This form of heat energy can travel in a vacuum.

Factors influencing temp

Latitude Altitude Distance from the sea Ocean currents Aspect Humidity and cloud cover Land surface

Latitude

Places near the Equator are hotter than places near the poles due to the angle at which sun’s ra strike the Earth

Amount of heat received by Earth’s surfaces decreases with latitude due to the decreasing angle of incidence Angle at which sun’s ray hits earth) of the sun’s ray

Latitude (cont)

In reality, Earth’s axis is tilted at an angle of 23.5º from the vertical

From June to Aug, there is a higher intensity of the sun’s ray in the northern hemisphere

The higher latitudes in the northern hemisphere therefore experience higher temperature in summer while the higher latitudes in the southern hemisphere experience low temp in winter.

http://thebrain.mcgill.ca/.../d_11_p_hor.html

Altitude

Temperature falls by 6.4ºC for every 1000m increase in height.

This fall in temperature is called the normal lapse rate.

Air is warmed by the heat radiated from the ground due to conduction and convection. It is much warmer as there is larger land

Most of Earth's surface gases is also concentrated at the Earth’s surface.

Altitude(cont)

Temp sometimes rise with altitude in the troposphere due to: Rapid outgoing terrestrial radiation on a

cloudless night. Cold air rolling down slope displacing the

Warmer air Warm air rises over cold air at a warm front Cold air undercutting warm air at a cold

front

Distance from the sea

Sea heats up and loses heat more slowly than land

Coastal area temperature is influenced. In temperate latitudes, coastal areas have a

smaller temperature range between summer and winter(not as hot in summer and not as cold in winter)

Inland areas far from the sea are not affected by the ocean thus have larger annual temp range.

Ocean Currents

Change in temperature is due to ocean currents in the area

Ocean current are set in motion by prevailing winds blowing over the surface

2 types of ocean currents: Warm – Originates from equator Cold – Originates from higher latitudes

Aspects

Refers to the direction of the slope of the land relative to the sun

More obvious in temperate regions rather than tropical regions

In northern hemisphere, south facing slope have higher temp than north facing slope

Faces the sun.

Humidity and cloud cover

Humidity is the state of the atmosphere with respect o its amount of water vapour

The higher the humidity, the more clouds there will be as clouds are formed by condensation of water vapour.

Thick cloud cover prevents solar radiation from entering in the day and outgoing terrestrial radiation escaping in the night.

Therefore, equatorial areas which have high humidity and thick cloud cover has low diurnal temp range.

Type of land surface

An area with vegetation is much cooler than an area of concrete.

Vegetation reduce the incoming radiation and prevents absorption of heat into the ground.

Concrete surfaces absorbs h eat quickly in the day and releases heat lowly at night.

“Urban Heat islands” Cause? Effects? (group work)

Instruments used to measure temperature Daily Maximum and minimum

temperatureDaily maximum temperature: the highest

temperature reading for the dayDaily minimum temperature: the lowest

temperature reading for the day

Maximum and Minimum Thermometer 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

The minimum thermometer works in the same way, but contains alcohol instead of mercury

Six’s Thermometer

Temperature Calculations

Diurnal Temperature range: Max temp – Min temp

Average Daily Temp (Max Temp + Min Temp) / 2 Total of hourly Temp / 24

Mean Monthly Temp Total of ave daily temp / total no. of days

Mean Annual Temp Total of 12 mean mthly temp / 12