Global Air Circulation

Global Air Circulation 🔄 1. General Circulation of the Atmosphere • Caused by: • Unequal heating of the Earth. • Rotation of the Earth. • Heat is transferred through large-scale wind systems. • Three levels of circulation: • Primary circulation – global wind belts. • Secondary circulation – regional systems. • Tertiary circulation – local winds (e.g., sea breezes). ☀ 2. Primary Circulation • Involves horizontal and vertical air movement. • G. Hadley (1735) proposed the first model. • Warm air at the equator rises (low pressure). • Cold air at the poles sinks (high pressure). • Air moves from high pressure (poles) to low pressure (equator) along the surface. 🌬 3. Tri-Cellular Circulation Model Due to the Coriolis force and Earth’s rotation, air movement is split into 3 circulation cells per hemisphere: 🟢 (i) Hadley Cell (0°–30° N/S) • Located between 0° and 30° latitude (equator to subtropics). • Intense heating at equator → air rises (low pressure). • Air cools and condenses → clouds and heavy convectional rainfall. • At 10 000 m, air diverges and sinks at 30° → subtropical high pressure. • Results in clear, dry weather. • Surface winds: Tropical easterlies / trade winds. 🟡 (ii) Ferrel Cell (30°–60° N/S) • Between subtropical high and sub-polar low. • Cool, dry air sinks at 30° → moves toward poles. • Meets cold polar air at 60° → polar front forms. • Air rises due to temperature difference, forming clouds and rain. • Surface winds: Westerlies (from west to east). 🔵 (iii) Polar Cell (60°–90° N/S) • Cold air sinks at poles → high pressure. • Air moves toward 60°, rises at polar front. • Surface winds: Polar easterlies (from east to west). 🌀 4. Coriolis Force • Caused by Earth’s rotation. • Deflects moving air: • Right in Northern Hemisphere. • Left in Southern Hemisphere. • Leads to curved wind patterns and helps form cells. 🌎 5. Intertropical Convergence Zone (ITCZ) • Found at equator. • Region where tropical easterlies converge. • Rising warm, moist air → low pressure, heavy rain and storms. 🗺 6. Global Pressure Belts Latitude Pressure Zone Air Movement 90°. Polar High (HP) Sinks 60° Sub-polar Low (LP) Rises 30° Subtropical High (HP) Sinks 0° Equatorial Low (LP) Rises 💨 7. Global Surface Wind Patterns Cell Latitude Range Winds Direction Hadley 0°–30° Tropical easterlies From east to west Ferrel 30°–60° Westerlies From west to east Polar 60°–90° Polar easterlies From east to west 🌡 8. Weather Patterns • Low pressure (equator & 60°): warm, rising air → clouds & rain. • High pressure (30° & poles): cold, sinking air → clear & dry.