Typhoon causes and characteristics

A tropical cyclone is a natural phenomenon that occurs in the western North Pacific Ocean and is accompanied by strong winds with a maximum sustained wind speed of 17 m/s or more near its centre.

It is called a typhoon, hurricane, cyclone, or Willy-Willy depending on the area where it occurs.

A typhoon is a tropical cyclone with strong winds of 17 m/sec or more near its centre.

Typhoons are called different names depending on where they form: Typhoon in the Northwest Pacific, Hurricane in North and Central America, Cyclone in the Indian Ocean, and Willy-Willy in the South Pacific.

Typhoons, on the other hand, usually occur in tropical waters where the sea surface temperature is above 27℃, and their lifespan is usually from one week to 10 days.

Typhoons generally move west-northwestward at the beginning of their development, but gradually move northward and follow a northeasterly path with prevailing westerly winds.

Causes of typhoons

A typhoon is a weather phenomenon in which warm air at low latitudes receives water vapour from the ocean and moves towards higher latitudes, accompanied by strong winds and heavy rain, in order to eliminate the thermal imbalance caused by the fact that the equator receives more heat from the sun than the poles.

The air over the ocean near the equator is hot, humid and unstable.

As a result, where the air pressure is weaker than the surrounding area, nearby air is drawn in and rises, forming small vortices that form cumulonimbus clouds.

Sometimes cumulonimbus clouds form squalls that produce rain.

When these vortices gather in one place under the influence of the northeast trade winds and grow in strength, they become the seeds of a typhoon.

Once the seed of a typhoon is formed, the cumulus clouds in the updraft release a lot of heat as they drop rain, which in turn strengthens the updraft again.

As this process is repeated many times, it becomes stronger and stronger, and finally becomes a typhoon.

Names of tropical cyclones depending on where they occur

Tropical cyclones have different names depending on the area where they occur: Typhoon, which occurs near the Philippines in the Northwest Pacific; Hurricane, which occurs in the North Atlantic, Caribbean, Gulf of Mexico, and eastern North Pacific; Cyclone, which occurs in the Indian Ocean, Arabian Sea, and Bay of Bengal; and Willy-Willy, which occurs in the South Pacific near Australia.

A total of 80 typhoons, hurricanes, and cyclones occur annually, with an average of 27 typhoons per year.

Typhoons and other tropical cyclones are characterised by circular isobars, not accompanied by fronts, originate and develop in tropical oceans because their energy is mainly the latent heat of water vapour, have a typhoon eye at the centre, and winds are particularly strong near the centre.

Wind speeds near the centre of a typhoon can exceed 17 metres per second and sometimes exceed 33 metres per second.

Typhoon criteria

The World Meteorological Organisation (WMO) classifies tropical cyclones with maximum sustained wind speeds near the centre of 33 m/s or more as typhoons (TY), 25-32 m/s as strong tropical storms (STS), 17-24 m/s as tropical storms (TS), and less than 17 m/s as tropical depressions (TD).

Typhoon intensity classification

Typhoons are classified into stages according to their intensity, and the criterion for classification is the maximum wind speed (10 minute average) near the centre.

Typhoon size classification

Typhoons are classified into stages based on the distance from the centre to the area with 15㎧ winds (‘high wind radius’).

Typhoon structure and characteristics

Typhoons have strong rain and winds near their centre.

The strongest storms range from 200 to 500 km from the centre of the typhoon, and as the pressure decreases and the wind speed increases toward the centre, there is a “typhoon eye,” an area without wind and clouds near the centre.

In the eye of a typhoon, which is 5 to 20 kilometres in diameter, winds are light and there are few clouds.

Outside the eye, the winds blow strongly in a counterclockwise direction from the periphery towards the centre, meaning that the typhoon itself is a strong mass of rain and wind blowing counterclockwise towards the centre of the typhoon.

This is why the right side of a typhoon’s path is more strongly affected by it.

On the right side of the typhoon’s path, the winds from the front and the winds blowing counterclockwise from the typhoon come into direct contact with each other, creating a strong vortex.

Meteorologists call the area to the right of the typhoon’s path the “dangerous semicircle” and the area to the left of the typhoon the “easy semicircle” because of these characteristics.

Meanwhile, as the typhoon approaches, the air pressure drops and the winds gradually increase.

Clouds first appear as high cirrus and cirrocumulus, then as mid-level cumulus, then as high altocumulus, then as high cumulus, and finally as giant cumulus.

The role of typhoons

Typhoons cause a great deal of damage because they contain strong winds and a lot of rain.

However, typhoons are also an important source of water, helping to relieve water shortages, transporting atmospheric energy accumulated in low latitudes to high latitudes, maintaining the global temperature balance between north and south, and revitalising the ocean ecosystem by mixing and circulating seawater and dissolving plankton.

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