4.8 (Earth's Geography & Climate) - 4.9 (El Nino & La Nina)
4.8 Earth’s Geography and Climate
Climate & Geography
Climate is determined by insolation (latitude affects angle and atmosphere).
Higher latitudes: cooler and less precipitation (especially 30°).
Equator: intense insolation, higher temperatures, rising air, and high precipitation.
Geography:
Mountains: disrupt wind and create rain shadow effects.
Oceans: moderate temperatures and add moisture.
Rain Shadows
Moist air from oceans hits the windward side of mountains, rises and cools (causing rain), resulting in lush vegetation.
Dry air descends on the leeward side, creating dry desert conditions.
Example: Eastern trade winds bring moisture to the E (windward) side of Andes, resulting in heavy rainfall; the W (leeward) side is arid, further exacerbated by 30° latitude high pressure.
FRQ 4.8 Practice
Expected precipitation for the indicated region of Mexico & Central America: As prevailing winds bring moisture (from Gulf of Mexico/Atlantic Ocean), rainfall occurs when it reaches land, especially along the eastern coast, despite the absence of mountains.
4.9 El Niño and La Niña
Global Ocean Surface Currents
Gyres: large circular ocean patterns influenced by global winds (clockwise in N hemisphere, counterclockwise in S).
Trade Winds (E → W between 0-30°) push equatorial currents, and Westerlies (30-60°) push mid-latitude currents.
Upwelling Zones: winds blowing warm surface water away from land draw up cold, nutrient-rich water, supporting productive fisheries.
Thermohaline Circulation
Connects all oceans, mixing salt, nutrients, and temperature.
Warm water from the Gulf of Mexico moves to poles, cools, evaporates, becomes saltier and dense, sinking, and spreading along the ocean floor before returning to the surface at upwelling zones.
El Niño Southern Oscillation (ENSO)
ENSO refers to shifting atmospheric pressure and ocean currents in the Pacific between South America and Australia/Southeast Asia.
Normal Year
Trade winds move water W → E; cooler water upwells off SA, creating productive fisheries and delivering precipitation to Australia & Southeast Asia.
El Niño
Weakening of trade winds reverses direction (W → E), leading to rising temperatures and precipitation in the Americas, suppressed upwelling, and drier conditions in Australia and Southeast Asia.
La Niña
Stronger trade winds lead to increased upwelling off SA, causing cooler conditions in the region and warmer weather in Australia & Southeast Asia.
Effects of El Niño and La Niña
El Niño | La Niña |
|---|---|
Suppressed upwelling; less productive fisheries in the South Atlantic | Stronger upwelling; better fisheries in the South Atlantic |
Warmer winter for much of North America | Cooler, drier weather in the Americas |
Increased precipitation and flooding in the Americas (especially West Coast) | Rainier, warmer conditions with increased monsoons in Southeast Asia |
Drought in Southeast Asia and Australia | Worse tornado activity in the US; increased hurricane activity in the Atlantic |
Weakened monsoon activity in India and Southeast Asia |
FRQ 4.9 Practice
Two environmental problems from El Niño: suppressed upwelling reduces fishery productivity; cooler, drier conditions lead to droughts in Australia and Southeast Asia.