Typhoon
Background - 1
Tropical storms
and Cyclone
A typhoon is a type of tropical cyclone that occurs in the ocean near latitude 5 to 20 degrees. Among the tropical cyclones, tropical cyclones that occur in the southwestern Pacific Ocean and blow toward East Asia are called typhoons. All tropical cyclones have the same structure, but typhoons are larger and more powerful. Typhoons occur most frequently between July and October, mainly at 5-25 degrees north latitude and 130-145 degrees east longitude.
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Properties of
tropical cyclone
Wind Speed
Typically, tropical cyclones with wind speeds of more than 110 km/h are classified as typhoons. Some very strong typhoons have a wind speed of 350km/h. Wind speeds are weaker than tornadoes, but the space scale and period are much larger.
Image from textbook
Pressure
The average sea-level pressure in the center of the typhoon is around 950mb, with strong typhoons at 870mb and weak typhoons at 990mb. The lower the central pressure, the stronger the typhoon is.
Image from textbook
Size
Typhoons are usually 600km wide spatially and range from days to weeks or more in time. In particular, typhoons are physically very large tropical cyclones, with almost twice the difference between central and outer air pressures. Therefore, strong force is formed in the horizontal structure of the typhoon, which is why the wind speed of tropical cyclones is strong.
Energy Source
Most of the energy sources of typhoons are latent heat caused by condensation. Therefore, typhoons usually occur in oceans with high water temperatures where many energy sources can be obtained.
In the Northern Hemisphere, typhoons occur most frequently in August and September, when sea-level temperature and evaporation rate in the tropical ocean is highest. On the contrary, the frequency of typhoons in the southern hemisphere is high in January and March. The temperature near the central core is much higher because the typhoon has a lot of heat energy in it.
Conditions Necessary
The conditions for the typhoon include high sea level temperature, sufficient moisture in the lower floors, unstable atmosphere, and mechanical conditions such as weak vertical shear in the wind, and convergence to the lower floors. Latent heat supply, a major source of energy for typhoons, is one of the most important conditions for occurrence and development of typhoons. Therefore, the occurrence of typhoons is highly affected by sea level temperature, usually at temperature above 27 degrees.
Form Process
Step 1 : Tropical Disturbance with little air pressure difference and no rotation is created.
Step 2 : Tropical disturbance is defined as tropical depression when the isobars are closed and air pressure differences begin to occur.
Step 3 : Tropical depression becomes a tropical storm when it becomes more powerful and reaches a speed of 63 km/h.
Step 4 : When tropical storms become more powerful, they become what we commonly call Typhon, Hurricane.(Typhoon : Extremely Strong Tropical Cyclone)
Coriolis Force
The typhoon is affected by Coriolis force. Coriolis force in the Northern Hemisphere acts counterclockwise, so the typhoon's rotation is counterclockwise. Conversely, the Coriolis force acts clockwise in the southern hemisphere, so the rotational direction of the typhoon in the southern hemisphere is clockwise.
Also, Coriolis force affects the rotational power of typhoons. Therefore, typhoons rarely form at latitudes of 0 to 5 degrees, where Coriolis force rarely works.