Cyclonic circulation
Topic: Atmospheric Pressure, Winds and General Circulation · NCERT: Class 11, Ch 9 "Atmospheric Circulation and Weather Systems"
Meaning
Cyclonic circulation is the flow of wind around a low-pressure centre. It turns anticlockwise in the Northern Hemisphere and clockwise in the Southern Hemisphere, because the Coriolis force (the turning effect of the Earth's spin) bends moving air. Surface air converges (flows in) towards the centre and rises. The rising air cools and forms cloud and rain. The Coriolis force is zero at the equator, so no cyclones form within about 5° of it.
Example
A tropical cyclone over the Bay of Bengal spins anticlockwise as it moves towards the Odisha or Andhra Pradesh coast, bringing strong winds and heavy rain.
Don't confuse with
- Anticyclonic circulation: this flows around a high, turns the opposite way, and makes air sink, giving clear and dry weather.
- Tropical cyclone: this is one type of storm that has cyclonic circulation. The circulation pattern also occurs in weak lows and temperate cyclones.