Parenting] Causes of Typhoons

In the tropical oceans, the sea surface is exposed to direct sunlight and the temperature of the sea water rises, the sea water easily evaporates into water vapor and spreads in the air, so the air on the tropical oceans has a high temperature and high humidity, and this air expands due to the high temperature, resulting in the density of the air decreasing in weight and weight, and the winds near the equator are weak, so the air rises easily and convection occurs, and the surrounding cooler air flows in to replenish it, and then rises, and so on and so forth. In the end, the entire air column will be filled with warmer, lighter and less dense air, resulting in the so-called tropical depression.

However, the flow of air is from high pressure to low pressure, just like water flowing from high to low, the air in the surrounding area with higher pressure must flow towards the lower pressure, thus forming "wind". In summer, as the direct sunlight area shifts from the equator to the north, the south-easterly trade winds from the southern hemisphere cross the equator and turn into south-westerly monsoon winds to invade the northern hemisphere, meeting with the northeasterly trade winds from the northern hemisphere, forcing the air to rise and increasing the effect of convection, and due to the difference in direction between the south-westerly monsoon winds and the northeasterly trade winds, these two winds often cause fluctuations and whirlpools when they meet. When the Southwest Monsoon and the Northeasterly Trade Winds meet, the radiative forcing and the original convection continue to deepen the low-pressure vortex, which means that the air around the vortex will flow faster towards the center of the vortex, and the faster the inflow, the higher the wind speed; when the maximum near-surface wind speed reaches or exceeds 17.2 meters per second, it will be called a "typhoon.

Typhoon structure:

Typhoons are very large in size, with an average radius of 200 to 300 kilometers. On weather maps, we can only use the dense, nearly circular isobars to indicate the location of the typhoon and the extent of the storm. We can see from weather satellite photos that the top of the typhoon is a roughly circular spiral of clouds, and that the winds inside the typhoon rotate counterclockwise around the center of the typhoon in the Northern Hemisphere (clockwise around the center in the Southern Hemisphere). Inside the typhoon, the results of observations made by weather reconnaissance aircraft flying into the typhoon from various heights and directions have shown that the typhoon is roughly a column of clouds with a very large radius, with varying heights from the top to the ground, and was once observed to be as high as 18,000 meters. The center of this huge column of clouds has no clouds, or has a very thin layer of clouds, and there is no stormy weather. This is the eye of the typhoon. From the eye of the typhoon, the clouds are the thickest and the wind and rain are the heaviest not far away from the eye of the typhoon, and the wind and rain are gradually weakening further out.

The eye of the typhoon:

A typhoon is a violent storm born on a tropical ocean. When you look at it from above, it looks like a big vortex with a circle of clouds surrounding the center, and the speed of rotation of the airflow gets faster and faster as it gets closer to the center, and you can see a hollow without clouds in the center, which is the eye of the typhoon. The eye of a typhoon varies in shape, mostly round and oval, sometimes unformed or with two eyes, and can be as small as a few kilometers in diameter or as large as one to two hundred kilometers in diameter. In general, the stronger the typhoon, the clearer the eye.
Definition of Typhoon Strength:

The strength of a typhoon is determined by the maximum wind speed near its center.

Tropical Depression → Maximum wind speed near the center is equal to or less than 33 knots (17.1 meters per second), i.e., equal to or less than a Category 7 wind.
Slight Typhoon → Maximum wind speeds near the center range from 34 to 63 knots (or 17.2 to 32.6 meters per second), which is equivalent to force 8 to 11 winds.
Moderate Typhoon → Maximum wind speeds near the center range from 64 to 99 knots (or 32.7 to 50.9 meters per second), which is equivalent to a force 12 to 15 wind.
Severe Typhoon → Maximum wind speeds of 100 knots (or 51.0 meters per second) or more near the center, equivalent to a force 16 or higher wind. In the Pacific Ocean, typhoons can occur throughout the year, but are usually most common between July and September.

Text/Central Weather Bureau