A2GEOGRAPHYREVISIONTROPICAL ENVIRONMENTS

7.1 TROPICALCLIMATES

KEYTERMSANDDEFINITIONSAir mass refers to large bodies of air where the horizontal gradients (variation) of the main physical properties, such as temperature and humidity, are fairly gentle.Relief rainfall is rainfall that occurs when air is forced to rise over high ground and mountains. As it rises, it cools and condenses, and rain may be formed.Convectional rainfall is rainfall formed during very hot conditions. The heated ground heats the air above it. As this warm air rises it cools, condenses and produces heavy rain.Intertropical convergence zone (ITCZ) is the area in which the north-east trade winds and the south-east trade winds converge. If there is a difference in temperatures between the winds, the warmer air rises over the denser, colder air and may produce rain.

KEYTERMSANDDEFINITIONSMonsoon refers to a seasonal reversal in wind systems, the most well-known being the monsoon of India and South East Asia. It is caused by seasonal variations in pressure over land and sea. There is low pressure over the land (e.g. Central Asia) in summer because it is so warm, whereas there is high pressure during winter, because the land is so cold. Air blows from high pressure to low pressure.Humid tropics are areas in the tropics that are wet all year round.

KEYTERMSANDDEFINITIONSSeasonally humid tropics are areas within the tropics where there is a distinct dry season as well as a wet season.El Niño is an irregular occurrence of warm surface water in the Pacific off the coast of South America that affects global wind and rainfall patterns.Ocean currents are the large-scale movement of water within the oceans. Warm ocean currents move water away from the Equator. In contrast, cold ocean currents move water away from cold regions towards the Equator. The major currents move huge masses of water over long distances.

TOPICSUMMARYAir masses are large bodies of air where the horizontal gradients (variation) of the main physical properties are fairly gentle.

● Air masses derive their temperature and humidity from the regions over which they lie.● Winds between the tropics converge on a line known as the ITCZ or equatorial trough.

TOPICSUMMARYCentres or ridges of high pressure imply subsiding air.

● The subtropical high or warm anticyclone is caused by cold air descending at the tropopause.● Warm currents carry water polewards and raise the air temperature of maritime areas. Cold currents carry water towards the Equator and so lower the temperatures of coastal areas.

ADDITIONALWORK1. Describe and explain the role of air masses in tropical environments.2. Briefly explain the functioning of the Indian monsoon. What impact does it have on India’s weather patterns?3. Outline the impacts of El Niño events.4. Compare and contrast the climate of humid tropical environments with that of seasonally humid environments.5. Describe and explain the main characteristics of tropical humid climates.6. Explain how different tropical climates may affect human activities.

SUGGESTEDWEBSITESwww.ace.mmu.ac.uk/eae/climate/older/tropical_climate.html for tropical climates.http://people.cas.sc.edu/carbone/modules/mods4car/africa-itcz/index.html for an animation of the ITCZ and climographs for selected cities.www.uwsp.edu/geo/faculty/ritter/geog101/textbook/climate_systems/tropical_monsoon_1.html for monsoon climates.www.elnino.noaa.gov for El Niño with links to FAQs and graphics.