Planetary Winds and Inter Tropical Convergence zone (ITCZ)

Planetary winds and Inter Tropical Convergence zone

90° N/S - Polar High & 60° N/S - Temperate low → winds blow from Polar high to Temperate low (Polar Easterlies)

60° N/S - Temperate low & 30° N/S - Sub-tropical high → winds blow from Sub-tropical high to Temperate low (Westerlies)

30° N/S - Sub-tropical high & 0° - Equatorial low → winds blow from Sub-tropical high to Equatorial low (Trade winds/Easterlies)

Planetary winds - These are the winds blowing over the planet all over the year.

Different types of Planetary winds -

1. Trade winds (Easterlies)
2. Westerlies
3. Polar Easterlies

1.   Trade winds 

• They blow from Sub-tropical high pressure belt to Equatorial low pressure belt.
• In Germany, the word trade means tract, i.e., blowing in same direction throughout the year.
• The trade winds are dry and stable in the area of origin. 
• Moving towards the equator, it takes up the moisture and causes precipitation in the eastern margin of the continents.
• On reaching the western margin of the continent, they are devoid of moisture and thus western margin of the continent which experiences off shore trade winds are majorly deserts. For example - Sahara desert, Kalahari desert, Thar desert, etc.

2.   Westerlies 

• They blow from Sub-tropical high to Temperate low.
• The vast landmass in the Northern hemisphere obstruct the wind flow, thus it is not so strong in the Northern hemisphere.
• But, in Southern hemisphere, they blow very strongly and consistently due to huge water expanse and are named differently at different latitudes. For example - Roaring 40's, Furious 50's, Shrieking 60's, etc.

3.   Polar Easterlies 

• They blow from Polar high pressure belt to Temperate low pressure belt.
• They are extremely cold, stable and dry.
• They blow for a long distance and affect the climate of the regions over which they are blowing.

Note - Winds are name from the direction they are coming. For example Easterlies wind comes from East direction (blows from East to West) while Westerlies wind comes from West dierection (blows from West to East)

ITCZ (Inter Tropical Convergence Zone) 

• It is the zone of convergence of trade winds from both the sides of Tropics and is centred along Equator extending upto 5° N to 5° S. 
• The conditions are low pressure, calm and windless.
• This is also known as Zone of Doldrums. 

(After converging, winds rises upward (also due to high temperature and convection current winds rises) → between 5° N to 5° S we do not feel much wind as there is negligible horizontal flow of wind. This results in the very calm and windless condition.)

Horse latitude - It is the zone of Sub-Tropical high pressure belt where due to vertically descending air, there are no horizontal movement of wind. Thus, creating a zone of light and calm winds at the Sub-tropical high and is known as Horse latitude.

(It is named so because during colonial period, horses were imported from Central Asia to South America and when the ships entered in this region, ships stopped moving because of windless and calm condition. Thus, in order to make it light so that the ship again started to move, they threw horses in the sea.)

Tricellular Meridional Circulation 

• Tricellular - Three cells, Meridional - Latitude & Circulation - wind movement, i.e., it is the wind movement consisting of three cells at different latitudes.
• Surface winds blow from high pressure to low pressure area, but in the upper troposphere the direction of the air circulation is opposite to the surface winds. 
• This together with the convection and subsiding current along the low pressure belt and high pressure belt results in three cellular circulations along each meridians known as Tricellular Meridional Circulations.
• The three cells are -

1. Hadley cell
2. Ferrel cell
3. Polar cell

Seasonal shifting of wind belts - With the movement of the sun, the wind belts also shifted Northward or Southward, the way pressure belts shifted.

Shifting of ITCZ (Inter Tropical Convergence Zone) - The way wind belts shifted with the movement of the sun, ITCZ also shifted Northward and Southward.

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Notes on other subjects

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Note - This is my Vision IAS Notes (Vision IAS Class Notes) and Ashutosh Pandey Sir's Public Administration Class notes. I've also added some of the information on my own. 

Hope! It will help you to achieve your dream of getting selected in Civil Services Examination 👍