Cyclones are a type of low-pressure environment with rapid inward air circulation. The word Cyclone comes from the Greek word Cyclos, which means snake coils.
Northern Hemisphere, air flows counterclockwise, while in the Southern Hemisphere, it circulates clockwise. Storms and poor weather are frequently associated with cyclones.
Anticyclone
- An anticyclone is just the opposite of a cyclone.
- The winds of an anticyclone swirl clockwise in the Northern Hemisphere around a high-pressure area.
- From above, air enters and sinks to the earth.
- Fairweather is usually associated with high-pressure centers.
Local Names of Cyclone
- Hurricanes – In the Atlantic and Eastern Pacific.
- Typhoons – In Southeast Asia
- Cyclone – In the Indian Ocean and Western Pacific around Australia.
Naming Of Cyclones
- Adopting names for cyclones makes it easier for people to remember, as opposed to numbers and technical terms.
- Cyclones that form in every ocean basin across the world are named by the regional specialized meteorological centers (RSMCs) and Tropical Cyclone Warning Centres (TCWCs).
- There are six RSMCs in the world, including the India Meteorological Department (IMD), and five TCWCs.
- The IMD is mandated to naming of cyclones as well as issuing advisories to 13 countries in the region on the development of cyclones and storms, namely Bangladesh, India, Maldives, Myanmar, Oman, Pakistan, Sri Lanka, Thailand, Iran, Qatar, Saudi Arabia, United Arab Emirates and Yemen.
Types of Cyclones
- Tropical cyclones
- Temperate cyclones
Tropical Cyclones
- Tropical cyclones are violent storms that originate over oceans in tropical areas and move over to the coastal areas bringing about large scale destruction caused by violent winds, very heavy rainfall and storm surges.
- Tropical Cyclones are one of the most devastating natural calamities in the world.
Temperate Cyclones or Extratropical Cyclones
- Mid-latitude depressions, temperate cyclones, frontal depressions, and wave cyclones are all names for extratropical cyclones.
- In both hemispheres, these are active above the mid-latitudinal zone between 35° and 65° latitude.
- The movement is from west to east, and it is most noticeable during the winter months.
- Polar and tropical air masses collide and generate fronts in these latitude zones.
Origin and Development of Temperate Cyclones
(a) Polar Front Theory
- According to this theory, warm-humid air masses from the tropics collide with dry-cold air masses from the poles, forming a polar front as a discontinuous surface.
- Such circumstances can be seen along the Tropopause and in subtropical high and subpolar low-pressure belts.
- The warm air from beneath is pushed upwards by the cold air. As a result of the reduced pressure, a void is generated. The surrounding air rushed in to fill the void, and when combined with the earth’s rotation, a cyclone forms, which moves westward (Jet Streams).
(b) Fronts
When two different air masses meet, the boundary zone between them is called a front. The process of formation of the fronts is known as frontogenesis. There are four types of fronts:
- Stationary: When the front remains stationary, it is called a stationary front.
- Warm: When the warm air mass moves towards the cold air mass, the contact zone is a warm front.
- Cold: When the cold air moves towards the warm air mass, its contact zone is called the cold front
- Occluded: When an air mass is fully lifted above the land surface, it is called the occluded front.
Air Masses
It is defined as a large body of air having little horizontal variation in temperature and moisture. The homogenous surfaces, over which air masses form, are called the source regions.
The air masses are classified according to the source regions. There are five major source regions. These are:
- Warm tropical and subtropical oceans;
- The subtropical hot deserts;
- The relatively cold high latitude oceans;
- The very cold snow covered continents in high latitudes;
- Permanently ice covered continents in the Arctic and Antarctica.
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