Cyclones and Associated Features

Cyclone refers to any low-pressure system with winds spiralling inwards. Cyclones revolve counterclockwise in the Northern Hemisphere, whereas they rotate clockwise in the Southern Hemisphere. Cyclogenesis is the process in which cyclones and their associated features develop. Cyclones and associated features have been observed on Earth and other planets, including Mars, Jupiter, and Neptune. The Great Red Spot on Jupiter is a cyclone circling it for 340 years. The Great Black Spot, a vast spinning storm, was discovered in the Southern Hemisphere of Neptune.

Cyclone Formation

Cyclogenesis is essential during the production or strengthening of a cyclone. It is an umbrella term that refers to several distinct processes resulting in a cyclone and associated features. Tropical cyclones are created near the equator over warm ocean water. The air near the ocean’s surface is warm and rises to the surface. This results in a low-pressure zone close to the surface. As a result, cooler air from the surrounding areas is drawn into the low-pressure area. The frigid air warms and grows moist, causing it to ascend. The rising warm moist air cools the water in the air, resulting in the formation of clouds. Later, the clouds and winds swirl and expand. The entire cycle repeats itself, resulting in a cyclone.

Types of Cyclones

Two types of cyclones may impact different parts of Earth. They are:

• Tropical cyclone
• Extratropical cyclones

• Tropical cyclone

A tropical cyclone is a weather phenomenon that consists of a swiftly rotating storm system with features such as a low-pressure centre, strong winds, and thunderstorms causing heavy rain.

Formation of tropical cyclones

The formation of a tropical cyclone is complex. A thin zone of low pressure spans across the equator in the tropics. The north-east and south-east trade winds blow on this zone’s northern and southern sides. The low-pressure area is heated by the warm tropical water, giving rise to air in discrete parcels, producing thunderstorms. This results in the flow of warm, wet, fast ascending air, forming a low-pressure centre or depression at the surface. Several trigger mechanisms are necessary to turn these cloud clusters into tropical cyclones, leading to extreme weather conditions. Various appropriate conditions may simultaneously trigger these mechanisms. The following factors lead to the formation of a tropical cyclone:

• A warm, moist air source originates from tropical waters with sea surface temperatures typically in the region of or exceeding 27 °C

• Winds flow from multiple directions converging at the ocean surface, causing air to rise and develop storm clouds.

• Low wind shear refers to winds that reveal no significant changes in height, leading the storm clouds to climb vertically to high elevations, enough distance occurs from the equator for spin or twists

Features of Tropical Cyclone

Some of the features of tropical cyclones are as follows.

1. Tropical cyclones are often lower in size than temperate cyclones. Their diameters range from 200 to 500 km.
2. They are more severe than temperate cyclones due to a large pressure gradient. The central pressure ranges from 50 to 60 mm of mercury. Tropical cyclones are associated with extremely high wind speeds.
3. The intensity of these low-pressure centres is remarkable over the oceans but weak on land. They become extinct as they reach the interiors of the continents. These cyclones are powered by the release of latent heat of condensation.
4. The mobility of tropical cyclones remains unpredictable. They can be stationary over a location for several days, resulting in significant precipitation. They travel on well-defined paths.
5. These cyclones can be classified into various categories based on their shape, size, and weather.
6. The circular centre of a tropical cyclone, known as its eye, is the most intriguing element of the cyclone. The eye’s diameter ranges from 8 to 50 km.

Extratropical cyclone

Extratropical cyclones and mid-latitude cyclones occur along frontal boundaries in the middle latitudes. The extratropical cyclones exhibit fewer winds and strong temperature gradients. The extratropical cyclone that affects the east coast of the United States is the nor’easter.

Formation of an extratropical cyclone

The Polar Front theory best explains the formation and evolution of temperate cyclones and their associated features. According to this theory, a polar front is generated when warm-humid air masses from the tropics collide with dry-cold air masses from the poles. As the cold air mass is denser and heavier, the warm air mass is pushed up. The contact of cold and warm air masses causes instability, resulting in reduced pressure at the intersection, particularly in the centre of the interactions, thereby generating a void. The surrounding air rushes in to fill the void, and a cyclone develops due to the earth’s rotation. Extratropical cyclones differ from the more violent tropical cyclones or hurricanes, which occur in generally constant temperature zones.

Features of extratropical cyclones

Storm systems that form outside the tropics, in the mid and high latitudes, are known as extratropical cyclones. Some of the features of these cyclones are as follows:

• These cyclones are formed at the polar front

• The front remains stationary at the initial phase

• Extratropical cyclones are also called mid-latitude storms and baroclinic storms

• Cold and warm air blow from the north and south of the front in the Northern Hemisphere, respectively

• When the pressure drops along the front, the cold air descends south, and the warm air moves north, causing an anticlockwise cyclonic circulation

• A well-built extratropical cyclone with cold and warm fronts results from cyclonic circulation

• The cold front advances quicker than the warm front and eventually overtakes it

• The cyclone evaporates as the warm air is entirely lifted and the front is occluded

• These cyclones can arise from land and water and cover a vast region

Conclusion

The tropical and extratropical cyclones have a specific formation process and possess several characteristics. Both of them are important natural phenomena which play a vital role in determining the climate and geographical variations in their respective areas of occurrence.