How are typhoons named? Is it feudal superstition?

my country borders the western Pacific Ocean and has always been a country severely affected by typhoons. In July, Typhoon Fireworks caused heavy rainfall in Henan and other provinces. Not long after, three typhoons, Lupit, Yinhe and Nida, were formed one after another.

Friends who surf the Internet frequently should have noticed that once a typhoon brings serious disasters, some netizens will say: "I think this typhoon is not far from being removed from the list."

Under what circumstances will a typhoon be removed from the list? How did those strange and fancy names of typhoons come from? Is it feudal superstition?

I’m here to answer your questions today!

How do typhoons get their names?

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 has named typhoons in the northwest Pacific after people, following the names of North Atlantic hurricanes, but this is only used informally by the Typhoon Warning Center. At this time, East Asian countries and regions still refer to typhoons by typhoon numbers. For example, in my country, 5612 represents Typhoon No. 12 in 1956.

Image from: Baidu Encyclopedia

However, since different agencies focus on different sea areas, the typhoon numbers are often different, which can easily cause confusion. Therefore, it is feasible and necessary to establish a unified typhoon naming rule for the entire northwest Pacific region.

In 1997, the World Meteorological Organization's Typhoon Committee decided that a new naming list would be used for typhoons generated in the northwest Pacific and the South China Sea starting from January 2000. The naming list contains 140 names, with 10 names provided by each of the 14 member countries and regions of the Typhoon Committee, which will be used in sequence.

The World Meteorological Organization (WMO) divides the global tropical cyclone monitoring areas into different regions. Tropical cyclones generated in Region IV are called "typhoons".

These names usually have characteristics of the member states.

For example, China used names of mythological or fictional characters such as "Wukong" and "Dianmu", Hong Kong named landmarks such as "Lion Rock" (a famous mountain in Hong Kong) and "High Island" (High Island Reservoir), and Micronesia provided "Nan Madur" (Nan Madur Ruins on Pohnpei Island) and "Ewini" (the storm god in the legend of Chuuk Island), etc.

Current typhoon naming list

Image from: China National Meteorological Administration

Although the right to name typhoons lies in the hands of each member, the authority to name typhoons that develop into tropical storm level lies in the hands of the Japan Meteorological Agency.

Therefore, a typhoon will only be officially named when the Japan Meteorological Agency determines that it has developed into a tropical storm level.

What are the rules for removing a typhoon from the list?

Most typhoons are removed from the list because they cause significant casualties and property losses.

After being removed, the typhoon name will no longer be used in circulation, so when people mention this name in the future, they will naturally refer to the typhoon when it was last used.

Super Typhoon Mangkhut is the 22nd named storm in the 2018 Pacific typhoon season. The name "Mangkhut" was provided by Thailand. Due to the severe impact of "Mangkhut" on the Philippines and southern China, the Typhoon Committee decided to remove "Mangkhut" from the list at its annual meeting in February 2019. According to the official website of the Central Meteorological Observatory on August 8, 2020, the name "Mangkhut" has been replaced by "Shanduoer" in the naming list.

At the Typhoon Committee meeting at the beginning of each year, countries and regions affected by disasters in the previous year will submit applications to remove typhoons from the list, and then discuss whether to remove them; if it is decided to remove them, the original nominating members will add new candidate typhoon names before the meeting next year.

There are also some typhoon names that were removed not because they caused huge disasters.

For example, in 2001, Typhoon No. 26 "Sonamu" did not cause serious damage, but because it was a rare typhoon generated near the equator, it was removed from the list as a "memorial"; in 2013, Typhoon No. 2 "Sonamu" was named by North Korea. Because the pronunciation "Sonamu" is close to the tsunami "Tsunami", it caused panic when it landed in Malaysia, so it was also removed from the list.

The name "Hua Mei" was provided by Macau. This name was permanently retired on January 1, 2004 and replaced by "Pipa".

What determines a typhoon's path?

To answer this question, you need to first understand some basic properties of typhoons.

A typhoon is essentially a deep cyclone that develops in tropical and subtropical seas, with a diameter usually ranging from hundreds to thousands of kilometers. Among weather systems, this diameter is roughly in the middle level, and some weather systems that are wider than it, such as subtropical high pressure and troughs and ridges in the westerly belt, can provide airflow to guide its movement - this is the main driving force for the movement of typhoons.

Among them, the subtropical high pressure, which has the largest overlap with the typhoon activity area, is the most important system. The typhoon is guided by the air currents on the edge of the subtropical high pressure. When it is on the south side of the subtropical high pressure, it is guided by air currents such as the easterly trade winds to move westward, and when it is on the western edge, it moves northward.

A diagram of the guiding airflow when the 2015 No. 13 typhoon "Soudelor" (typhoon symbol indicated by the black circle) approached the coast of my country. The red circle is the subtropical high pressure, and the southeast wind (white arrow) located southwest of its center caused Soudelor to move northwest and eventually land in Taiwan and Fujian.

Year after year, the subtropical high pressure has a significant movement with seasonal changes, following the sun to the north in spring and summer, and returning to the south to avoid the cold wind in autumn and winter. Therefore, typhoons generally follow this pattern - in winter and spring, the path is biased to the south, which may affect the Philippines and Vietnam; while in summer and autumn, it is biased to the north, mostly affecting China, Japan, South Korea and other places.

In addition to the subtropical high pressure, there are other factors that affect the path of typhoons. One of the more special factors is the mutual rotation effect when two typhoons exist at the same time and are close to each other. This phenomenon was first discovered by Dr. Fujiwara of Japan and is also called the Fujiwara effect. At this time, the two typhoons will move counterclockwise around their mass centers, and the smaller typhoon will be more affected.

Examples of the Fujiwara effect in 2000 Typhoon Saomai (right) and Typhoon Bopha (left). The broken lines correspond to their paths.

In addition, when the circulation and weather systems in a region change dramatically, the typhoon's path may change dramatically or take many rare paths.

When a typhoon makes landfall, where will the rainfall be heaviest?

According to the conventional typhoon structure, the closer to the typhoon center the typhoon eye is, the stronger the wind and rain will be. But on this basis, rainfall will also be affected by other factors.

The first is the typhoon's "danger semicircle". The dangerous semicircle is located on the right side of the typhoon's direction of travel, and the wind speed is usually stronger than on the left side.

Schematic diagram of the danger semicircle of Typhoon Mangkhut on the evening of September 15, 2018

Image from: China Meteorological Enthusiasts

There are two reasons for the appearance of the danger semicircle. The main reason is that the wind we actually feel is the result of the superposition of the wind caused by the typhoon itself (caused by the strong pressure gradient) and the speed of the typhoon.

On the right side of the direction of travel, the typhoon's own wind direction is basically the same as the direction of movement speed, so the superposition effect causes the actual wind speed to be higher; on the left side of the direction of travel, the two directions are in opposite directions, and such superposition causes the actual wind speed to be weaker.

The typhoon's own wind speed and movement speed have a superimposed effect

Image hand-painted by the author

Secondly, the dangerous semicircle is also related to the weather system around the typhoon.

In summer, subtropical high pressure often appears on the right side of the typhoon's moving direction. At this time, the pressure gradient between it and the low pressure center of the typhoon is greater, which will cause stronger winds on the right side of the typhoon's moving direction. However, this does not apply in all cases - for example, in autumn, when a typhoon moves northward along my country's offshore, the Chinese land on the left side (west side) of its moving direction has gradually been controlled by cold high pressure, and the western coast often has strong northerly winds.

Weather map of the middle troposphere (500hPa) when Typhoon Soudelor No. 13 in 2015 approached the coast of my country. At this time, Soudelor was moving in a northwest-west direction (black arrow), and the red circle is the subtropical high pressure. It can be seen that the subtropical high pressure is located on the right side of its moving direction, and the wind force on this side is stronger.

In addition, the impact of terrain on wind power is also very important. Coastal open areas, highlands and other terrain areas will become areas with stronger winds when a typhoon lands; and for the coastal areas of South China, when the wind direction changes from northerly winds to southerly winds after the typhoon lands, the wind changes from the rugged terrain and strong friction land to the open sea surface, and sometimes there will be such a situation that the "returning south wind" is stronger than the north wind before landing. For cities, taller buildings make the streets "narrow tubes". When a typhoon affects a city, if the wind direction happens to be parallel to the street, the wind will be stronger.

When it comes to rainfall, there are even more things to pay attention to.

Generally speaking, there are spiral rain belts and cantilever structures on the periphery of typhoons. If you happen to be "hit" by them, there will be heavy rainfall and even the influence of active severe convective systems; but since these are belt-like structures, as the typhoon moves, it is likely to enter between the two spiral rain belts, and the wind and rain in this area are relatively light, similar to the situation of "showers".

Weather radar map of Zhejiang Province at midnight on August 9, 2019, when Typhoon Lekima, the ninth typhoon of 2019, was about to land in Zhejiang Province. The red, black and purple circles respectively marked the outer severe convection area, the spiral rain belt area and the core eyewall cloud area.

After going deep inland, the core area of ​​the typhoon will be quickly destroyed by friction with the land, and the area near the center may not be the area with the heaviest rainfall. If it is summer, the areas on the south and east sides connected to the monsoon water vapor transport channel often have stronger rainfall; if it is autumn or the typhoon is moving northward on land, the heaviest rainfall will occur on the north side.

Radar map of the East China region late at night on July 28, 2021. At this time, the center of Typhoon Fireworks No. 6 in 2021 is not far to the northwest of Bengbu (black circle), but the main rainfall area (red circle) is already located in the trough area to the north of the typhoon center.

For thousands of years, human civilization has gained continuous understanding through its encounters and struggles with these giant figures dancing in the tropical mist; but these understandings are still just a drop in the ocean; there are more unknowns hidden in these towering figures, which are also the frontiers that researchers in meteorology-related fields are exploring.

I hope that when we encounter this ocean power again in a future with climate change, we can do so more peacefully and calmly.

Written and photographed by Fengyun Mengyuan

WeChat Editor | Happy

Source | Museum