Chapter 11- Tropical climates Tropical climates are somewhat variable In terms of moisture In terms of temp on a day-night cycle And somewhat consistent In terms of annual temp In terms of incoming solar radiation

Diurnal compared to annual temperature ranges defines the tropics

Tropics (shaded land) have a greater diurnal temperature range than annual temperature range

Moisture is what indicates classification and prevalent life forms in the tropics Af climate - dominated by mT airmasses wet all year round; rain forest biome Aw, Am, BSh climates - dominated by alternating mT and cT airmasses; wet season vs dry seasons; savanna biome BWh climate - dominated by cT all year; dry all year; desert biome

Hadley cell circulation is critical toward understanding tropical climates controls location of ITCZ (rising, unstable air- Low pressure) shifts north or south with seasons shifts to accommodate land vs water Controls wet vs dry seasons in tropical climates with that trait. Controls location of permanently dry regions by location of sinking air (High pressure)

ITCZ extremes in geographic position

Moisture plays a critical role in temperature too much --> cools temps considerably by blocking incoming radiation and lowering surface temp too little, and temps plummet at night as no water in the atmosphere to catch outgoing longwave radiation coming the land surface

ITCZ means converging air, moist air, rising air, unstable air, low pressure and precipitation Temps are moderated in the rain forests not the blazingly hot jungles often portrayed in Hollywood still warm, and definitely muggy “feels” much warmer due to high relative humidity. humans cooling system thwarted

Amount of rainfall varies, but the frequency is more important that the amount Daily rainfall events are somewhat different than in the mid-latitudes Thunderstorms dominate all year round in tropics more intense, but shorter lived and more frequent than mid latitude cyclonic storms with fronts

Common diurnal rainfall in the tropics

The tropical rainforest Species diversity- one of the most diverse environments on the planet One hectare can contain 200+ species of trees Stratified system enables numerous micro-climates within the forest Global benefits biomass production is immense Oxygen production is matched only by marine organisms, but per capita is unmatched

Sometimes “helped” by oceanic or mountain systems Tropical deserts found in persistent high pressure zones associated with Hadley circulation cells Tropical deserts have relatively higher temps than do mid-latitude deserts Sometimes “helped” by oceanic or mountain systems Can cover extremely large areas Sahara 3500 k mi2 Australian 1300 k mi2 Kalahari-Namib 220 k mi2

Cold ocean currents affect desertification Cool air holds less moisture Cool air sinks (stable conditions = high pressure) Stable air + low moisture = low rainfall Coastal South America (Chilean desert) Coastal south Africa (Namib desert) Western Mexico (Baja Peninsula)

Tropical deserts are extremely sensitive to climate change One of the first climate zones to feel the effects of changes in global climates wetter = plant growth explodes lakes and rivers form animal and people inhabit drier = desert expands surface moisture diminishes animals and people adapt, leave or die

Desert storms not much in the way of rainfall very windy because of few obstructions and severe thermal lifting creates sandstorms and dust devils

Pre-colonial Post-colonial