2.3.2 Climate

Tropical rainforest:

Location: Tropical rainforests are located in a band around the equator, mostly in the area between the Tropic of Cancer (23.5° N latitude) and the Tropic of Capricorn (23.5° S latitude). This 3,000 mile (4800 km) wide band is called the "tropics." Tropical rainforests are found in South America, West Africa, Australia, southern India, and Southeast Asia.

Mean temperature of the hottest month: about 25°C

Mean temperature of the coldest month: about 25°C

Annual temperature range: less than 5°C

Rainfall – amount: exceeds 2000mm

Rainfall – seasonal distribution: same throughout year

Wind: low

Cloud: heavy

Humidity: high

Pressure: low

Tropical desert:

Location: between 5° and 30° north and south of the equator

Mean temperature of the hottest month: 30°C

Mean temperature of the coldest month: no less than 18°C

Annual temperature range: less than 5°C

NOTE: during the day it can get to 50°C but during the night it gets to about 0°C so the average is lower.

Rainfall – amount: less than 250mm in a year

Rainfall – seasonal distribution: irregular rainfall

Wind: strong

Cloud: virtually cloudless skies

Humidity: low

Pressure: high

Contributing factors:

distance from oceans;

winds blow over large areas of land;

winds blow offshore/do not blow from sea hence no source of moisture/water sources;

low humidity;

lack of evaporation;

sparse vegetation;

lack of transpiration;

high air pressure;

descending air;

cold offshore currents etc.

Factors affecting temperature:

-latitude: closer to the equator = higher temperature

-distance from the sea: coastal area = warmer winters and cooler summers

-prevailing winds: the seasonal difference in heating between land and sea (land heats up more quickly in summer and cools more rapidly than the sea in winter) affects the temperature of the prevailing wind. Warm prevailing wind = rise in temperature

-ocean currents: warm currents raise winter temperatures in coastal areas; cold currents cool them down in summer

-altitude: higher altitude = lower temperature (1° per 100m)

-Pressure systems & wind belts:

• The angle of the sun creates pressure belts: low pressure at the equator & mid latitudes; high pressure at the tropics & poles.
• Wind blows out of high pressure into low pressure creating a global pattern of winds.
• The direction of the prevailing winds affects the climate of places. Making it warmer or colder, wetter or dryer.
• The pressure & wind belts move with the overhead sun. So prevailing wind directions can change with the seasons.

Types of rainfall:

Convectional rain:

1. The sun’s rays heat the ground.
2. This heats the air above it so it rises.
3. As the air rises it cools.
4. Condensation point is reached & cloud forms producing thunder storms.

Frontal Rain:

This happens mostly at mid-latitudes where warm tropical air meets cold polar air.

1. Warm air moves towards the cold air.
2. Being less dense the warm air rises over the cold air.
3. The air cools as it rises.
4. Condensation occurs & clouds form to produce rain.

Relief Rain:

1. When warm, moist air hits mountains it is forced to rise.
2. As it rises it cools. Condensation occurs producing clouds & rain or snow.
3. On the leeward side the cool air sinks getting warmer.
4. The air behind the mountains is warmer & dryer so there’s less rain. The rain shadow area.