Important Air Circulation Cells and Permanent Winds

Important air circulation cells and important permanent winds is an important topic in general geography. This is a conceptual topic that needs special attention. Questions are asked very frequently in the exams and aspirants need to focus carefully so that they will be able to understand the concept. This article gives clarity about different air circulation cells and also about different permanent winds.

Planetary Wind Patterns Depend on :

• Latitudinal variation of atmospheric warming.
  
• the shifting of pressure belts;
  
• Movement of the belt following the apparent course of the Sun.
  
• Distribution of land mass and water bodies.
  
• Rotation of the earth on its axis.
  
• The pattern of movement of planetary winds is called the general circulation of the atmosphere. The general circulation of the atmosphere also causes the circulation of seawater, which affects the Earth’s climate.

Different Types of Air Circulation Cells

1. Hadley cell :

• Air in the Intertropical Convergence Zone (ITCZ) rises due to cyclonic convection. Negative pressure is then caused by high levels of solar radiation. Winds from the tropics meet in this low-pressure zone.
  
• It occurs between the Tropics and the Equator 
  
• The converging air rises with the convective cell. It reaches an altitude of 14 km at the top of the troposphere and migrates towards the poles. This causes air to accumulate around 30 degrees north and 30 degrees south latitude. Some of the accumulated air sinks to the seafloor and forms a subtropical anticyclone. Another reason for subsidence is the cooling of the air as it reaches latitudes 30 degrees north and 30 degrees south.
  
• Below near the surface, air flows as an easterly wind toward the equator. Easterly winds from both sides of the equator converge in the Intertropical Convergence Zone (ITCZ). Such surface-to-top circulation and vice versa are called cells. Such cells are called Hadley cells in the tropics.
  

2. Ferrel cells :

• In the mid-latitudes, the circulation consists of descending cold air coming from the poles and rising warm air blowing from subtropical anticyclones. On the surface, these winds are called westerly winds, and the cells are known as Ferrel cells.
  
• Occurs between 30 degrees N and S to 60 degrees N and S.
  

3. Polar cells :

• At the polar latitudes, the cold, dense air near the poles relaxes and blows toward the mid-latitudes as the Far East Wind. The cell is also known as the polar cell.
  
• This cell is the weakest and smallest among the rest.
  
• Occurs between 60 and 70 degrees north and south, to the poles.

4. Walker cells :

• Warming and cooling of the Pacific Ocean are most important in terms of global atmospheric circulation.
  
• The warm waters of the central Pacific are slowly drifting toward the South American coast, displacing the cold Peruvian currents. Such occurrences of warm water off the coast of Peru are known as El Niño. El Niño events are closely associated with pressure changes in the central Pacific and Australia. This change in pressure over the Pacific Ocean is known as the Southern Oscillation. 
  
• The combination of the Southern Oscillation and El Niño phenomenon is known as ENSO. In years of strong ENSO, large-scale global climate change occurs. There will be heavy rains on the dry west coast of South America, droughts in Australia, and sometimes India, and floods in China. This phenomenon is closely monitored in many parts of the world and used for long-term forecasting.

Permanent Winds:

These are planetary winds that blow widely across continents and oceans. The two most well-understood and most important winds for climate and human activity are the trade winds and the westerlies.

1. Trade winds

• Trade winds blow from a subtropical high to an equatorial low. They are therefore confined to regions between 30°N and 30°S across the Earth’s surface.
  
• They flow as northeast journeys in the northern hemisphere and southeast journeys in the southern hemisphere. This deflection in the ideally expected north-south direction is explained by the Coriolis force and Farrell’s law.
  
• The trade winds are descending and steady in their region of origin (the subtropical high), and when they reach the equator they pick up moisture on the way, making it wetter and warmer.  
  
• The two hemispheric trade winds meet at the equator and converge to rise, causing heavy rainfall. The eastern part of the trade winds associated with cold currents is drier and more stable than the western part of the ocean.
  

2. Westerlies

• The west wind is the wind that blows from the subtropical high-pressure zone to the subarctic low-pressure zone. It blows from the southwest to the northeast in the Northern Hemisphere and from the northwest to the southeast in the Southern Hemisphere. Southern hemisphere westerly winds are stronger and more consistent due to the vast expanse of water, while northern hemisphere westerly winds are less stable due to the uneven topography of the vast landmass.  
  
• Westerly winds are most developed between 40° and 65° south latitude. These latitudes are often referred to as his roaring 40’s, roaring his 50’s, and screaming his 60’s.
  
• The extremes of the westerly wind are highly variable.  These winds cause periods of high humidity and weather fluctuations.
  

3. Polar Easterlies

• The Far East wind is a dry, cold prevailing wind that blows northeast to southwest in the northern hemisphere and southeast to northwest in the southern hemisphere.  
  
• They blow from the sub-cyclonic and extreme anticyclone regions.