These Atmospheric Circulation and Weather Systems Class 11 Geography Notes explain atmospheric pressure, wind systems, general circulation of atmosphere, air masses, fronts, cyclones and local winds. The chapter discusses pressure gradient force, Coriolis force, Hadley Cell, Ferrel Cell, tropical cyclones, extra tropical cyclones and thunderstorms.
These NCERT notes are useful for UPSC, SSC, Railways, State PSC, CUET and CBSE Board Exams. The chapter is important for understanding global wind circulation, pressure belts, weather systems and atmospheric disturbances responsible for rainfall and storms.
This chapter explains atmospheric pressure, pressure belts, wind systems, air masses, fronts, cyclones and general circulation of atmosphere. It highlights how pressure differences and Earth’s rotation create global wind systems and weather phenomena across the world.
Atmospheric pressure is the weight of air column exerted over unit area from mean sea level to the top of atmosphere.
| Level | Pressure | Temperature |
|---|---|---|
| Sea level | 1013.25 mb | 15.2°C |
| 1 km | 898.76 mb | 8.7°C |
| 5 km | 540.48 mb | –17.3°C |
| 10 km | 265 mb | –49.7°C |
Isobars are lines joining places having equal pressure.
Pressure belts shift north and south with the apparent movement of the Sun.
Pressure gradient is the rate of pressure change with distance.
Coriolis force is caused by Earth’s rotation and named after Gaspard Coriolis.
Wind blowing parallel to isobars when pressure gradient force balances Coriolis force.
El Nino is a warm ocean current near the Peru coast.
Pressure changes over Pacific Ocean are known as Southern Oscillation.
Cold dense air flowing downhill.
Air mass is a large body of air with uniform temperature and humidity.
| Air Mass | Meaning |
|---|---|
| mT | Maritime Tropical |
| cT | Continental Tropical |
| mP | Maritime Polar |
| cP | Continental Polar |
| cA | Continental Arctic |
Front is the boundary between two air masses.
Formation process of fronts.
Cold air moves towards warm air.
Warm air moves towards cold air.
Tropical cyclones are violent storms formed over tropical oceans.
| Region | Name |
|---|---|
| Indian Ocean | Cyclone |
| Atlantic Ocean | Hurricane |
| Western Pacific | Typhoon |
| Western Australia | Willy-willies |
Calm central region of cyclone.
Rise of sea water during cyclone causing coastal flooding.
Tornado occurring over sea is called waterspout.
Atmospheric pressure is the weight of air exerted over unit area.
Isobars are lines joining places having equal pressure.
It is the force caused by Earth’s rotation that deflects winds.
ITCZ is the low pressure zone near the equator where trade winds converge.
The calm central region of a tropical cyclone is called the eye.