Global atmospheric circulation shapes Earth's climate, driven by uneven heating and pressure differences. The Coriolis effect deflects winds, creating distinct circulation cells: Hadley, Ferrel, and Polar. These cells influence weather patterns worldwide.

The Intertropical Convergence Zone (ITCZ) plays a crucial role in global climate. It's where trade winds meet, causing rising air and heavy rainfall. The ITCZ's seasonal migration affects tropical wet and dry seasons, impacting ecosystems and weather patterns.

Atmospheric Circulation Drivers and Patterns

Drivers of global atmospheric circulation

• Uneven heating of Earth's surface causes temperature gradients
  • Solar radiation more intense at equator than poles (23.5° tilt of Earth's axis)
  • Equatorial regions absorb more heat (tropical rainforests)
• Atmospheric pressure differences drive circulation
  • Warm air rises at equator creating low pressure (Doldrums)
  • Cool air sinks at poles creating high pressure (Polar highs)
• Coriolis effect influences wind direction
  • Earth's rotation deflects moving objects including air
  • Deflection to the right in Northern Hemisphere (Hurricane tracks)
  • Deflection to the left in Southern Hemisphere (Cyclone tracks)

Atmospheric circulation cells

• Hadley cell spans equator to 30° latitude
  • Warm air rises at equator, moves poleward, cools, descends around 30°
  • Low pressure at equator (Intertropical Convergence Zone) and high pressure at 30° (Subtropical highs)
  • Responsible for trade winds and tropical rainforests
• Ferrel cell located 30-60° latitude
  • Driven by Hadley and Polar cells
  • Low pressure at 60° (Subpolar lows) and high pressure at 30° (Subtropical highs)
  • Indirect circulation with air rising at 60° and descending at 30°
  • Associated with mid-latitude weather systems (Extratropical cyclones)
• Polar cell spans 60° latitude to poles
  • Cold air descends at poles, moves equatorward, warms, rises around 60°
  • High pressure at poles (Polar highs) and low pressure at 60° (Subpolar lows)
  • Brings cold, dry air from polar regions to mid-latitudes

Major global wind patterns

• Trade winds in Hadley cell (equator to 30°)
  • Blow from northeast in Northern Hemisphere (Hawaii)
  • Blow from southeast in Southern Hemisphere (Galapagos)
  • Converge at Intertropical Convergence Zone
• Westerlies in Ferrel cell (30-60° latitude)
  • Blow from southwest in Northern Hemisphere (Gulf Stream)
  • Blow from northwest in Southern Hemisphere (Roaring Forties)
  • Responsible for majority of mid-latitude weather
• Polar easterlies in Polar cell (60° to poles)
  • Blow from northeast in Northern Hemisphere (Siberian Express)
  • Blow from southeast in Southern Hemisphere (Antarctic winds)
  • Transport cold, dry air from polar regions

Intertropical Convergence Zone and Precipitation

Role of Intertropical Convergence Zone

• ITCZ is region near equator where trade winds converge
  • Characterized by rising motion, low pressure, high precipitation
  • Migrates seasonally following area of maximum solar heating (23.5° tilt)
• Key component of Hadley cell circulation
  1. Rising motion in ITCZ drives Hadley cell
  2. Air moves poleward at upper levels
  3. Air returns to equator at surface as trade winds
• Influences global precipitation patterns
  • High precipitation due to converging winds and rising motion (Amazon rainforest)
  • Equatorial regions experience high rainfall year-round (Tropical monsoons)
  • Seasonal migration affects wet and dry seasons in tropics (Harmattan wind)