Summary

Let’s cover what we learned in this lesson!

• The motion of air and water in the climate system is driven by four main forces:
  • The pressure gradient force initiates wind by moving air from high to low pressure areas.
  • The Coriolis force deflects wind to the right in the Northern Hemisphere and to the left in the Southern Hemisphere due to Earth’s rotation.
  • Friction slows down winds near the surface, especially over rough terrain, but decreases with altitude.
  • Gravity drives vertical air motion, influencing updrafts and downdrafts, critical for storms and other weather phenomena.
• These forces combine to create three main atmospheric circulation cells:
  • The Hadley cell circulates warm air up at the equator and down at the subtropics, leading to tropical rainforests and desert climates. It is thermally-direct.
  • The Ferrel cell mixes warm and cool air in the mid-latitudes, resulting in variable weather patterns. It is thermally-indirect.
  • The Polar cell circulates cold air around the poles, creating polar deserts.
• These circulation cells define Earth’s major climate zones: wet tropics, dry deserts, and polar regions.
  • Wet tropics are shaped by the constant rising of warm, moist air at the equator, leading to frequent rainfall and lush vegetation.
  • Deserts are formed by subtropical high-pressure zones where dry air descends and suppresses precipitation.
  • Mid-latitude temperate zones experience variable weather due to the interaction between warm tropical air and cold polar air, resulting in four distinct seasons.
  • Polar deserts are created by cold, descending air that limits moisture and precipitation, resulting in icy conditions.
• Oceans also play a key role in climate regulation:
  • The wind-driven circulation is precisely what it sounds like – wind in the atmosphere pushes ocean water. Included in this circulation are ocean gyres moving warm water from the tropics to higher latitudes, impacting regional climates.
  • The thermohaline circulation or “ocean conveyor belt” moves water based on temperature and salinity differences, redistributing heat globally.

Understanding these systems is crucial for grasping how heat and moisture move around the planet, shaping both local weather and global climate patterns. Now that we have a good grasp of why the climate system does what it does, let's move on to talking about “natural variability” within the climate system -- behaviors we observe that occur on timescales longer than sensible weather!