Pressure Belts and Wind Systems: Planetary and Local Winds
July 19, 2026
Pressure Belts and Wind Systems: Planetary and Local Winds
Introduction
Atmospheric pressure differences drive wind systems worldwide. The uneven heating of the Earth's surface creates global pressure belts, which in turn generate planetary wind systems — trade winds, westerlies, and polar easterlies. Superimposed on these are seasonal winds (monsoons) and local winds influenced by regional geography.
Factors Affecting Atmospheric Pressure
Key Factors
Temperature: Warm air expands, rises → low pressure; cold air contracts, sinks → high pressure
Altitude: Pressure decreases with height; ~half of atmosphere below 5.6 km
Earth's rotation (Coriolis force): Deflects winds to the right in NH, left in SH
Water vapour: Humid air is lighter than dry air → lower pressure
Pressure Measurement
Unit: Millibar (mb) or hectoPascal (hPa)
Standard sea-level pressure: 1013.25 mb
Isobars: Lines joining places of equal pressure on maps
Global Pressure Belts
Seven Pressure Belts (Idealized)
Pressure Belt
Latitude
Characteristic
Equatorial Low
0° (5°N-5°S)
Low pressure; high temperature, rising air; doldrums
Tropical Easterly Jet (summer) and Subtropical Westerly Jet (winter)
Mascarene High (Southern Indian Ocean high pressure)
El Niño / La Niña modulation
Conclusion
Global pressure belts and wind systems form the primary circulation of the atmosphere, redistributing heat and moisture across the planet. Planetary winds (trades, westerlies, polar easterlies) are the dominant large-scale patterns, while local winds (sea breezes, katabatic winds, monsoons) are shaped by regional geography. Understanding these systems is essential for climatology, agriculture, and disaster preparedness.
Practice Questions
Explain the global pressure belt system. How does the seasonal migration of ITCZ influence the Indian monsoon?
Distinguish between planetary winds and local winds with examples.
What are jet streams? Discuss their role in influencing weather and climate.