Chapter 6 Weather

Chapter 6

Weather

Weather• An area’s short term (usually a day) atmospheric

condition• Differs from climate which is weather over a long

period of timeClimate• Determined by average temperature and

precipitation over a period of time (usually a year)• Climate then determines an areas biome

Global Air CirculationCaused by 4 factors1. Uneven heating of the Earth’s

surface- poles vs equator2. Seasons caused by the tilt of the

Earth3. Rotation of the Earth- spins faster at

the equator than at the poles causing prevailing winds

4. Evaporating water creating convection cells

60ºN

30ºN

0º

30ºs

60ºS

Cold deserts

Westerlies Forests

Hot desertsNortheast trades

ForestsEquator

Hot deserts

Forests

Southeast trades

Westerlies

Cold deserts

Physical properties of atmosphere

• Warm air, less dense (rises)

• Cool air, more dense (sinks)

• Moist air, less dense (rises)

• Dry air, more dense (sinks)

Fig. 6.5

Moist surface warmed by sun

Flows toward low pressure,picks up moisture and heat

Warm,dry air

Hot, wetair

Falls, is compressed, warms Rises, expands, cools

Heat releasedradiates to space

LOWPRESSURE

HIGHPRESSURE

Cool, dryair

Condensationand

precipitation

HIGHPRESSURE

LOWPRESSURE

Dry woodlands and shrublands (chaparral)

Temperate grassland

Temperate deciduous forest

Boreal forest (taiga), evergreen coniferousforest (e.g., montane coniferous forest)

Arctic tundra (polar grasslands)

Tropical savanna,thorn forest

Tropical scrub forest

Tropical deciduous forest

Tropical rain forest,tropical evergreen forest

Desert

Ice

Mountains(complex zonation)

Semidesert,arid grassland

Tropic ofCapricorn

Equator

Tropic ofCancer

Polar (ice)

Subarctic (snow)

Cool temperate

Warm temperate

Dry

Tropical

Highland

Major upwelling zones

Warm ocean currentCold ocean current

River

Ocean Currents and Climate• Ocean currents help to mix

nutrients and dissolved oxygen, as well as influence the climate of coastal regions

• Winds blowing westward push surface waters away from the coast and cold, nutrient rich water takes its place (upwelling)

• Upwelling leads to high productivity

Normal Conditions

El Nino Conditions

La Nina Conditions