Example 1
Under what conditions does a typhoon form, which way does it rotate in the Northern Hemisphere, and what wind speed marks a typhoon?
1A typhoon is a tropical low-pressure system that forms over tropical seas where the water is about 27°C or higher and warm water vapor is supplied.
2When the maximum wind speed near the center reaches 17 m/s or more it is classed as a typhoon, and in the Northern Hemisphere it rotates counterclockwise.
▸ Forms = tropical sea at 27°C or higher / wind speed 17 m/s or more, rotates counterclockwise in the Northern Hemisphere
A typhoon is a huge low-pressure system that draws its energy from the water vapor of a warm sea.
Example 2
How does the weather differ between the eye at the center of a typhoon and the eyewall around it, and why is the right side of its path more dangerous?
1The eye has sinking air at the center, so winds are weak and the sky is clear, while the eyewall gathers the strongest winds and heaviest rain.
2On the right half of the path the wind around the typhoon blows the same way as its travel, so the wind speeds add up, which is why it is called the dangerous semicircle.
▸ Eye = weak and clear, eyewall = strongest wind and rain / right half = wind plus travel speed add up, so dangerous
Even within one typhoon, the center, the eyewall, and the left and right halves differ greatly in strength.
Unit Test
Which statement about typhoons is correct?
①A typhoon forms over cold polar seas
②Winds are strongest in the eye of a typhoon
③In the Northern Hemisphere a typhoon rotates counterclockwise
④A typhoon grows stronger when it makes landfall
⑤Pressure rises toward the center of a typhoon
▸ ③ In the Northern Hemisphere a typhoon rotates counterclockwise
1A typhoon forms over tropical seas at 27°C or higher (① wrong), and winds are weak in the eye (② wrong).
2On land the supply of water vapor is cut off and a typhoon weakens (④ wrong), and pressure falls toward the center (⑤ wrong); in the Northern Hemisphere a typhoon rotates counterclockwise (③ correct).