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my country borders the western pacific ocean and has always been severely affected by typhoons. super typhoon makar landed in wenchang, hainan on the afternoon of september 6 and then entered the beibu gulf, becoming the strongest autumn typhoon (typhoons that landed from september to november) to land in my country since 1949, and caused extremely strong impacts on hainan, western guangdong, and southern guangxi.

according to information released by the central meteorological observatory on the afternoon of september 7, the intensity of "makar" has increased instead of decreased after entering the beibu gulf. the maximum wind speed near the center is currently maintained at level 17 (60 meters/second), making it the strongest typhoon ever to appear in the beibu gulf since meteorological records began.

as of 12:00 on september 7, the disaster has affected three provinces and regions: hainan, guangdong, and guangxi.1.227 million people were affected to varying degrees, 3 people died and 95 people were injured。

image source: screenshot of cctv news video

netizens from all over the country have paid attention to the typhoon disaster in hainan and guangdong and guangxi, and have also discussed this strong typhoon. how are typhoons formed? why is this typhoon named "capricorn"? what does it mean that typhoon capricorn, which was mentioned in the hot search yesterday, has completed its first "eyewall replacement"?

what is a typhoon?

a typhoon is a deep (reaching the troposphere at an altitude of about 12 to 18 kilometers from the ground) system active in tropical and subtropical regions. it is a tropical cyclone characterized by a lower central pressure than the surrounding area and a cyclonic circulation of wind fields.

typhoons and hurricanes are essentiallytropical cyclonethe only difference between them is their activity areas - the typhoon activity area is the marginal seas such as the northwest pacific ocean and the south china sea north of the equator and west of the 180° longitude, while in the atlantic ocean and the northeastern pacific ocean east of the 180° longitude and north of the equator, tropical cyclones are called hurricanes, while tropical cyclones in the indian ocean are called cyclonic storms.

the relationship between them is like that between potatoes and potatoes, which are different names for the same thing.

how was typhoon capricorn formed?

why is it so strong as an autumn typhoon?

the formation of a typhoon requires the following conditions:

1. sufficiently warm seawater(usually the sea surface temperature needs to be above 26.5℃, and the thickness of the warm water layer under the sea surface must be sufficient), which can provide enough water vapor for evaporation and latent heat energy released during condensation; if there is additional water vapor brought in by atmospheric circulation, it can further promote its development.

2. the spawn location is a certain distance from the equator in the north-south direction., ensuring that there is enough coriolis force to provide the initial rotational power;

3. the difference in wind direction and speed between the upper and lower levels (called vertical wind shear) is small enoughthis is the only way to ensure that the heat released by the condensation of low-altitude water vapor during the rise will not be "blown away" by the high-altitude wind, but can be retained here and heat this air mass, allowing the low pressure on the ground to develop further.

4.a sufficiently significant outflow of air at high altitudein this way, the air mass that is heated and lifted to high altitude by the latent heat of water vapor can radiate to the surrounding area, thereby further promoting the lifting of air masses on the ground and in low altitudes and the decrease of air pressure.

if these conditions are met in front of the typhoon during its movement, it will develop significantly. this time, typhoon makar was born from a tropical disturbance near the east coast of the philippines, and eventually developed into the strongest typhoon this year (so far) under the right conditions.

the current sea surface temperature chart shows that the waters south of 35°n in the northwest pacific are basically above 26.5℃, which can support the development of typhoons. image source: easterlywave.com

therefore, there are the most typhoons in the northwest pacific in the summer and autumn from june to october each year. this is not only because the sea temperature is relatively high during this period, which is conducive to the formation of convective clouds, but also because the summer monsoon prevails in the south china sea and the low-latitude northwest pacific at this time. a large amount of water vapor is carried from the southern hemisphere by the monsoon circulation across the equator, which can greatly promote the development of initial tropical disturbances to form typhoons.

at the same time,although there are slightly fewer typhoons in autumn than in summer, their overall intensity is slightly stronger than in summer.however, due to the southward movement of the autumn subtropical high pressure, although the overall intensity is strong, the number of typhoons landing in my country is also decreasing - capricorn has become the strongest autumn typhoon to land in my country.

the average number of typhoons generated and landed in my country each month from 1991 to 2020. image source: china weather

how are typhoons named?

the names of typhoons have gone through two stages of evolution over the past few decades.

since 1947, the u.s. joint typhoon warning center in guam has named typhoons in the northwest pacific after people, following the names of north atlantic hurricanes, but these names are only used informally by the typhoon warning center. at this time, east asian countries and regions usually directly refer to typhoons by typhoon numbers. for example, in my country, 5612 represents typhoon no. 12 in 1956.

however, since different agencies focus on different sea areas, typhoon numbers are often different, which can easily cause confusion in terms of communication.as meteorological satellites have achieved monitoring of the entire sea area and exchanges between countries and regions have become increasingly close, it has become feasible and necessary to establish a unified typhoon naming system for the entire northwest pacific region.。

the world meteorological organization typhoon committee meeting in 1997 decided that starting from january 1, 2000, a new naming table would be officially used for typhoons generated in the northwest pacific and the south china sea (see zone iv in the figure below).

the division of tropical cyclone responsibility areas around the world. image source: world meteorological organization

the naming list contains a total of 140 names, with 14 members of the typhoon committee (in alphabetical order: cambodia, china, north korea, hong kong, japan, laos, macao, malaysia, micronesia, philippines, south korea, thailand, the united states, and vietnam) each providing 10 names, and the naming list is composed in the above order and used in a circular manner.

the current typhoon naming table. image source: china national meteorological administration

these names usually carry the characteristics of the member's country and region. for example, china named mythological or fictional characters such as "wukong", "dianmu" and "fengshen". hong kong, china named landmarks such as "lion rock" (a famous mountain in hong kong) and "high island" (high island reservoir). micronesia provided "nan madul" (nan madul ruins on pohnpei island) and "awini" (the storm god in the legend of chuuk island), etc.

andthis time, "capricorn" was provided by japan.——all typhoon names provided by japan are names of constellations, such as "hato" which caused serious impact on the pearl river delta region in 2017; but if it is the most well-known twelve constellations, besides capricorn, there is only libra.

so what are the rules for removing a typhoon from the list?most typhoons are removed from the list because they caused significant casualties and property damage.after being removed from the list, the typhoon name will no longer be used in a circular manner, so when people mention this name in the future, they will naturally refer to the typhoon when it was last used.

at the typhoon committee meeting at the beginning of each year, the countries and regions affected by the disaster in the previous year will apply for delisting, and then the meeting will discuss and decide whether to delist; if it is decided to delist, the original nominating members will add new candidates for typhoon names before the next year's meeting, and the next year's meeting will decide whether to officially use them. with the current disaster situation of capricorn in my country and the philippines (and it will soon cause serious impact in vietnam), the probability of delisting is very high.

however, some typhoon names were not removed from the list because they caused huge disasters. for example, the 2001 typhoon no. 26 "huamei" did not cause serious damage, but because it was a rare typhoon generated near the equator (the coriolis force near the equator is very weak and usually cannot support the formation of typhoons), it was removed from the list as a "commemoration"; the 2013 typhoon no. 2 "qingsong" was named by north korea. when it landed in malaysia, it caused panic because its pronunciation sonamu was close to the english name of tsunami, tsunami, so it was also removed from the list.

what does the trending term “eyewall replacement” mean?

a more vivid analogy:eyewall replacement is like a typhoon's "molting" and "self-rescue"。

schematic diagram of the vertical structure of a typhoon

the eyewall is a circle of strong winds and rains near the center of a typhoon, and is a manifestation of strong convection.its evolution and development are related to the typhoon's angular momentum and the transport of water vapor in the periphery, and the mechanism is complex. during the eyewall replacement process, the old eyewall near the center is significantly weakened, while the outer eyewall has not yet fully developed, indicating that the wind and rain in the center of the typhoon have weakened;after the eyewall replacement is completed, it indicates that the wind and rain near the typhoon center will strengthen again.。

on the radar map, you can see the "double eyelid" structure of the inner and outer eye walls of typhoon makar (inner eye wall in the blue circle, outer eye wall in the red circle).

when typhoon makar approached the landfall area, the inner eyewall was still remnant (blue circle), while the outer eyewall was relatively intact (black circle). base map source: central meteorological observatory.

on the 5th, after the typhoon was replaced, it significantly strengthened from the night of the 5th to the morning of the 6th. on the 7th, makar strengthened again in the beibu gulf, becoming the strongest typhoon in this area after the 2014 super typhoon "wilmason", causing quite severe impacts on northern hainan, guangdong's leizhou peninsula and other places, and also brought huge pressure to post-disaster recovery work.

for thousands of years, human civilization has gained continuous understanding through encountering and fighting with these giant figures dancing in the tropical mist; however, these understandings are still just a drop in the ocean; there are more unknowns hidden in these towering figures, which are also the front that researchers in meteorology are exploring. i hope that when we encounter this ocean power again in the future of climate change, we can pass through it more safely and calmly.