General circulation of atmosphere

General circulation of the atmosphere

The general circulation of the atmosphere is the pattern of planetary wind movements. 

The following factors influence the pattern of planetary winds: 

• Latitudinal variance in atmospheric heating.
• Appearance of Pressure belts.
• The ITCZ migration along with the apparent path of the sun.
• The globe has widely distributed continents and oceans.
• The earth’s rotation.
• The overall circulation of the atmosphere influences ocean water circulation, which determines the earth’s climate.

InterTropical Convergence Zone

• Because of convection generated by high insolation, the air in the Inter-Tropical Convergence Zone (ITCZ) rises, resulting in low pressure. The tropics’ winds converge in this low-pressure zone.
• Along with the convective cell, the convergent air rises too. It goes towards the poles, reaching the top of the troposphere up to an altitude of 14 km. Around 30° N and S, air accumulates as a result of this.
• A subtropical high arises when some of the collected air lowers to the ground.

• In the ITCZ, easterlies from both sides of the equator converge. 

Types of Cells

• Hadley cells: Cells that circulate from the surface upwards and vice versa are known as Hadley cells in the tropics.
• Ferrel Cells: The circulation in the middle latitudes is dominated by sinking cold air from the poles and rising warm air from the subtropical high. These winds are known as westerlies at the surface, and the cell is known as the Ferrel cell.
• Polar Cells: The cold and dense air at the poles dissipates and blows as the polar easterlies into middle latitudes are known as the Polar cell. 

Characteristics of cells

• These three cells set the tone for the atmosphere’s overall circulation.
• The transfer of heat energy maintains general circulation from lower to higher latitudes.
• The oceans are affected by the overall circulation of the atmosphere.
• Large-scale atmospheric winds initiate large and slow-moving ocean currents.
• Oceans, in turn, contribute energy and water vapour to the atmosphere.

Seasonal Winds: 

• Due to shifting zones of the highest heating, pressure, and wind belts, the pattern of wind circulation changes with the seasons.
• The monsoons, particularly over Southeast Asia, are the most noticeable result of such a shift.

Local Winds:

• Due to differences in the heating and cooling of earth surfaces, the cycles that develop daily or annually can create several local winds. 

Land and Sea Breezes:

• over the land the air rises giving rise to a low pressure area
• the sea is relatively cool and the pressure over sea is relatively high
• pressure gradient from sea to land is created and the wind blows from the sea to the land as the sea breeze

Mountain and valley winds

• during the day time, slopes get heated up and air moves upslope 
• to fill up the resulting gap the air from the valley blows up the valley, this wind is a valley breeze
• during the night time, the slopes get cooled and the dense air descends into the valley as the mountain wind 

Air Masses

• air with distinctive characteristics in terms of temperature and humidity is called an air mass
• air masses are classified according to the source regions
• air masses are recognised as Maritime tropical (mT); Continental tropical (cT); Maritime polar (mP); Continental polar (cP); and Continental arctic (cA)
• tropical air masses are warm and polar air masses are cold

Tropical Cyclones 

• Tropical cyclones are violent storms that originate over oceans in tropical areas and move over to the coastal areas bringing about large scale destruction caused by violent winds, very heavy rainfall and storm surges
• This is one of the most devastating natural calamities

Thunderstorms and Tornadoes

• Thunderstorms are caused by intense convection on moist hot days
• A thunderstorm is a well-grown cumulonimbus cloud producing thunder and lightning
• From severe thunderstorms sometimes spiralling wind descends like a trunk of an elephant with great force, with very low pressure at the centre, causing massive destruction on its way, and such a phenomenon is called a tornado
• The violent storms are the manifestation of the atmosphere’s adjustments to varying energy distribution
• The potential and heat energies are converted into kinetic energy in these storms and the restless atmosphere again returns to its stable state

Conclusion

The general circulation of the atmosphere is the pattern of planetary wind movements influenced by many factors of planetary winds, such as latitudinal variance in atmospheric heating, appearance of pressure belts, ITCZ migration along with the apparent path of the sun, earth’s rotation and overall circulation of the atmosphere influences ocean water circulation, which determines the earth’s climate.