Major Pressure Belts of the Earth
•The Unequal Heating of the Earth and its Atmosphere •The Rotation of the Earth
Unequal heating
• Due to spherical shape • Equatorial region • Polar region
Rotation of the Earth
• Earth flings bulk of air towards the Equator • Four major belts – - Equatorial Low pressure belt – Doldrums - Sub-Tropical High Pressure Belt – Horse Latitudes - Sub-polar Low Pressure Belt – Storminess - Polar High Pressure Belt – cold and heavy
Polar High
Sub-Polar Low
Sub-Tropical High
Equatorial Low Sub-Tropical High
Sub-Polar Low
Polar High
Seasonal Shifting of Pressure Belts
• Due to temperature on the surface of the Earth – apparent migration of the Sun. • Directly overhead at the Equator • On March 21 and Sept 23 • Dec and June – moves northward • June and Dec – moves southward
On June 21 – All the pressure belts move towards north. Mar 21 and sept, 23 – vertically over the equator Remains in doldrum through out the year
Westerlies
Horse Latitude NE Trade Winds Doldrums SE Trade Winds Horse latitude
On Dec 22 – pressure belts move towards south
Westerlies
Major Wind System of the Wind
• Planetary Winds • Periodic Winds • Variable Winds
Planetary Winds
Planetary Winds- Wind blow all the time in the same area 1. Tropical Latitudes 2. Temperate Latitudes 3. Polar Region
Tropical Latitudes
• Sub-tropical – Equatorial are trade winds • Due to coriolis effect they blow from North to East. • NE in Northern hemisphere • SE in Southern Hemisphere
Temperate Latitude
• Sub Tropical to Sub Polar – Westerlies • SW in Northern Hemisphere • NW in Southern Hemisphere
Polar Region
• Polar High to Sub polar low – Polar Easterlies • NE in northern Hemisphere • SE in Southern Hemisphere
Characteristics of Trade Winds
• Regular in strength and direction • Permanent winds • Follow the movement of the sun
Characteristics of Westerlies
1. Sub Tropical to Sub Polar – Westerlies 2. Blow from SW in Northern Hemisphere NW in Southern Hemisphere 3. Not constant in strength and direction.frequent cyclones and anticyclones 4. More strong and constant in Southern Hemisphere – Roaring Forties 5. Follow the movement of the sun.
Characteristics of Polar Winds
Polar High to Sub polar low – Polar Easterlies NE in northern Hemisphere SE in Southern Hemisphere These are the deflected the most Take variety of direction due to local weather disturbance – in North • Regular in South • Extremely cold and dry • • • • •