Earth's atmosphere is in constant motion, driven by uneven heating and the planet's rotation. This creates a complex system of wind patterns and pressure zones, from the humid tropics to the arid subtropics and beyond.

These global circulation patterns shape our weather and climate. They influence everything from the formation of deserts and rainforests to the paths of storms and the distribution of temperature and rainfall across the planet.

Atmospheric Circulation Drivers and Patterns

Drivers of atmospheric circulation

• Uneven heating of Earth's surface by the Sun
  • More solar radiation received near the equator (tropics) compared to the poles (arctic regions)
  • Creates temperature gradients between the equator and the poles, driving atmospheric circulation
• Pressure gradients resulting from uneven heating
  • Warm air rises near the equator, creating low pressure (Intertropical Convergence Zone)
  • Cold air sinks near the poles, creating high pressure (polar highs)
• Coriolis effect caused by Earth's rotation
  • Deflects wind to the right in the Northern Hemisphere (clockwise)
  • Deflects wind to the left in the Southern Hemisphere (counterclockwise)

Solar radiation and Earth's rotation

• Solar radiation creates convection cells
  • Hadley cells: Rising air near the equator, descending air around 30° latitude (subtropical highs)
  • Ferrel cells: Rising air around 60° latitude (subpolar lows), descending air around 30° latitude
  • Polar cells: Rising air around 60° latitude, descending air near the poles (polar highs)
• Earth's rotation causes the Coriolis effect
  • Deflects wind direction, creating easterly (trade winds) and westerly winds (prevailing westerlies)
  • Influences the direction of trade winds, westerlies, and polar easterlies, shaping global wind patterns

Global Wind Belts and Pressure Systems

Major wind belts and pressure systems

• Intertropical Convergence Zone (ITCZ)
  • Area of low pressure near the equator where the northeast and southeast trade winds converge
  • Associated with rising air, cloudiness, and heavy rainfall (rainforests)
• Trade winds
  • Blow from the northeast in the Northern Hemisphere and southeast in the Southern Hemisphere
  • Located between the equator and 30° latitude, providing consistent winds for sailing routes
• Subtropical high-pressure belts
  • Located around 30° latitude in both hemispheres (Bermuda High, Pacific High)
  • Associated with descending air, clear skies, and dry conditions (deserts)
• Prevailing westerlies
  • Located between 30° and 60° latitude in both hemispheres
  • Blow from the southwest in the Northern Hemisphere and northwest in the Southern Hemisphere, influencing weather patterns
• Polar front
  • Boundary between cold polar air and warmer mid-latitude air around 60° latitude
  • Associated with the formation of mid-latitude cyclones and frontal systems
• Polar easterlies
  • Located between 60° latitude and the poles
  • Blow from the northeast in the Northern Hemisphere and southeast in the Southern Hemisphere, bringing cold air to lower latitudes

Impact on temperature and precipitation

• Hadley cells
  1. Rising air near the equator leads to heavy rainfall in the ITCZ (Amazon Rainforest)
  2. Descending air around 30° latitude creates arid conditions in the subtropical high-pressure belts (Sahara Desert)
• Ferrel cells
  • Rising air around 60° latitude contributes to the formation of the polar front and mid-latitude cyclones, bringing precipitation (temperate rainforests)
  • Descending air around 30° latitude reinforces the subtropical high-pressure belts, promoting dry conditions
• Polar cells
  • Descending air near the poles leads to cold, dry conditions (polar deserts)
• Jet streams
  • Strong upper-level winds that influence the movement of air masses and weather systems
    • Polar jet stream: Located near the polar front, affects mid-latitude weather (storm tracks)
    • Subtropical jet stream: Located near the subtropical high-pressure belts, influences the movement of tropical weather systems (hurricanes)