General Circulation Of The Atmosphere: Geography Notes For UPSC

Definition of General Circulation of the Atmosphere

• The pattern of the movement of the planetary winds is called the general circulation of the atmosphere.

Factors for General Circulation of the Atmosphere

• The pattern of planetary winds largely depends on:
  • Latitudinal variation of atmospheric heating
  • The emergence of pressure belts
  • The migration of belts following the apparent path of the sun
  • The distribution of continents and oceans
  • The rotation of the earth
• The general circulation of the atmosphere also sets in motion the marine water circulation which affects the climate of the Earth.
• The air at the ITCZ (Inter Tropical Convergence Zone) upsurges because of convection caused by high insolation and low pressure is generated.
• The winds from the tropics join this low-pressure zone.
• The joined air upsurges along with the convective cell.
• It reaches the top of the troposphere up to an altitude of 14 km.
• It further moves toward the poles. This causes accumulation of air at about 30^o North and South.
• Another reason for sinking is the cooling of air when it reaches 30 degrees North and South latitudes.
• Downward near the land surface, the air flows towards the equator as the easterlies.
• The easterlies from either side of the equator converge in the Inter-Tropical Convergence Zone (ITCZ).
• Such circulations from the surface up and vice-versa are called cells.
• This type of cell in the tropics is called the Hadley Cell.
• In the mid-latitudes, the circulation is that of dipping cold air that comes from the poles and the mounting warm air that blows from the subtropical high.
• At the surface, these winds are called westerlies and the cell is known as the Ferrel cell.
• At polar latitudes, the cold dense air subsides near the poles and blows towards middle latitudes as the polar easterlies. This cell is called the polar cell.
• These Ferrel cells, Hadley Cell, and polar cell set the configuration for the general circulation of the atmosphere.

General Atmospheric Circulation and its Effects on Oceans

• The general circulation of the atmosphere also influences the oceans.
• Warming and cooling of the Pacific Ocean are most significant in terms of general atmospheric circulation.
• The warm water of the central Pacific Ocean gradually drifts towards the South American coast and substitutes the cool Peruvian current.
• Such presence of warm water off the coast of Peru is known as the El Nino.
• The El Nino is associated with pressure variations in Australia and the Central Pacific.
• This variation in pressure conditions over the Pacific is known as the southern oscillation.
• The combined phenomenon of El Nino and southern oscillation is known as ENSO.