Geography's Effect on Earth's Climate

Objective

  • Describe how Earth's geography affects weather and climate.
  • Essential knowledge: Weather and climate are affected by the sun's energy and geographic factors.
  • Specific focus: Rain shadow effect and its impact.
  • Science skill: Explain relationships between environmental concepts represented visually.

Climate and Insolation

  • Climate is largely determined by insolation (intensity of incoming solar radiation).
  • Equator receives most direct sunlight, resulting in the warmest temperatures and highest precipitation.
  • Air rises at the equator, leading to high precipitation.
  • Air sinks around 30 degrees north and south, leading to dry conditions and deserts due to the Hadley cell.
  • Temperature generally decreases with distance from the equator.
  • Insolation is spread over a larger area due to Earth's curvature and atmosphere.

Regional Climate Factors

  • Location of mountains affects wind movement, producing the rain shadow effect.
  • Location and temperature of oceans add moisture to the air.
  • Oceans moderate temperature by absorbing heat when it's hot and releasing heat when it's cold.

Rain Shadow Effect

  • Mountains near the coast cause the rain shadow effect.
  • Warm, moist air from the ocean hits the windward side of the mountain.
  • The air rises and cools, causing water vapor to condense and fall as rain.
  • Windward side: lush, green vegetation.
  • Leeward side: dry, desert-like conditions due to loss of moisture.

Andes Mountains Example

  • Andes Mountains in South America demonstrate the rain shadow effect.
  • Prevailing winds between 30 degrees and the equator are from east to west.
  • Eastern side (windward): moist air from the Atlantic Ocean, lush vegetation, high precipitation.
  • Western side (leeward): Atacama Desert, dry conditions.
  • Atacama Desert is located on the western coast of South America.
  • Air loses moisture on the windward side and descends dry on the leeward side.

Latitude and the Hadley Cell

  • Being at 30 degrees latitude contributes to dry conditions due to the Hadley cell.
  • Air mass sinking at 30 degrees latitude is very dry.
  • Proximity of the Atacama Desert to 30 degrees south latitude contributes to its dryness.

Visual Evidence

  • Aerial photos show lush vegetation on the eastern side of the Andes and dry conditions on the western side.
  • Precipitation maps show heavy rainfall on the eastern side and low precipitation on the western side.

Tectonic Plates

  • Tectonic plate boundaries impact the climate of South America.
  • Subduction of the oceanic plate beneath the continental plate formed the Andes Mountains.
  • More dense oceanic plate subducts or is forced beneath a less dense continental plate. When that oceanic plate subducts the continental plate, it's going to force some magma and some lithosphere upwards, which is actually what forms that narrow band of coastal mountains—in this case, it's the Andes.

Practice FRQ 4.8

  • Describe the regional precipitation pattern in Mexico and Central America.
  • Consider prevailing wind directions and local bodies of water.
  • Southern region near the equator has more rainfall due to warmer air.
  • Northern region closer to 30 degrees latitude has less precipitation.
  • Prevailing winds from east to west collect moisture from the Gulf of Mexico and Atlantic Ocean.
  • Eastern coast receives more rainfall due to moisture deposition from the ocean.
  • Local bodies of water produce higher precipitation levels; for example, cities along the lakeshore in Michigan (Holland, Muskegon) receive more rain and snow than inland areas (Grand Rapids).