What was the weather like before the typhoon?

Typhoon is a strong storm that occurs in the tropical oceans of the northwest Pacific Ocean and the South China Sea. You must have seen a vortex appear in the river from time to time. In fact, a typhoon is an air vortex, which rotates around its center in the atmosphere and moves forward at the same time. It rotates counterclockwise in the northern hemisphere and clockwise in the southern hemisphere. Meteorology calls the vortex in the atmosphere a cyclone, because the vortex in the typhoon atmosphere is produced on the surface of the tropical ocean, so it is called a tropical cyclone.

Why is it called typhoon? Some people say that in the past, people didn't understand that typhoons originated in the Pacific Ocean and thought that this huge storm came from Taiwan Province Province, so it was called a typhoon. Some people think that the typhoon hit Guangdong Province the hardest, and it evolved from Cantonese "gale".

In fact, almost all countries and regions located on the west coast of the ocean are affected by tropical marine cyclones, but people in different regions have given it different names.

Typhoons in the northwest Pacific and the South China Sea, hurricanes in the Atlantic Ocean, the Caribbean Sea, the Gulf of Mexico and the East Pacific, tropical storms in the Indian Ocean and the Bay of Bengal, and tropical cyclones in Australia.

Naming and numbering of typhoons

The naming, definition, classification and determination of the center position of tropical cyclones are different in different countries and methods, even in the same country, they are not exactly the same among different meteorological stations. Therefore, it often causes various misunderstandings and confusion in use.

In order to change this situation, the meteorological department adopted the method of naming typhoons. At the end of World War II, the United States identified four groups of girls' names with English letters (except Q, U, X, Y and Z) for the first time to name Atlantic hurricanes. Each group is arranged in alphabetical order. Such as the first group: Anna, B 1anche (Blanche), Camille. Te (Camil.te), etc. Until wcnda (wenda); Group 2: A 1nla (alma), BECL (J/ (Becky), Sierra (Celia), etc. Until Willner; The third and fourth groups are also named according to A to W. When the plane detects a typhoon, it will be named according to the order in which it appears. The first one will be named Anna, and the second one will be named B 1Anche, etc. When the first group of names is used up, use the names headed by the second group A again. The first typhoon name in the second year is followed by the last typhoon name in the previous year, which can be recycled. It is impossible for a typhoon to occur in any area in a year to exceed the sum of these four groups of names. Take the Pacific Northwest, which has the most typhoons in the world, for example, there are no more than 50 typhoons a year. Therefore, in the same year, it is impossible for each region to have the same name. Of course, the names of typhoons will be repeated in different years. Therefore, in front of the typhoon name. Be sure to indicate the year to show the difference.

Starting from 1959, China began to adopt the intensity and method of typhoon numbering. All typhoons formed or invaded in the Pacific Ocean and South China Sea to the west of east longitude 150 degrees and north of the equator are numbered according to the order of occurrence. For example, the first typhoon number of 1999 is 990 1, the second typhoon number is 9902, and so on.

This typhoon numbering method has been adopted by meteorological stations in many countries and regions. Some countries have long been accustomed to using the English names of typhoons, except the numbers. At the same time, it also indicates the English name of the typhoon.

Classification of typhoons

In meteorology, tropical cyclones are classified according to their intensity. The United Nations World Meteorological Organization has formulated an internationally unified classification standard for tropical cyclones:

A tropical cyclone with a central maximum wind force of 7 (< 17. 1 m/s =) is called a tropical depression;

The maximum wind force in the center reaches 8-9 (17.2-24.4m/s), which is called a tropical storm.

A tropical cyclone with a central maximum wind force of10-1(24.5-32.6 m/s) is called a typhoon or hurricane.

The source of typhoon

There are 80- 100 typhoons in the world every year (tropical cyclones in other areas are also called typhoons here), most of which occur in the Pacific Ocean and the Atlantic Ocean. According to statistics, typhoons in the western Pacific are mainly concentrated in four areas:

1, east of the Philippine Islands, near the Ryukyu Islands. This area has the most typhoons in the northwest Pacific Ocean, and typhoons occur almost all year round. June-June mainly occurs in the waters near Samar Island and Mindanao Island in the Philippines south of 15 degrees north latitude. After June, the occurrence area expanded northward, appearing in the waters near Luzon Island to Ryukyu Islands in the Philippines from July to August, moving southward to the waters near Luzon Island in September, and moving to the waters south of 10 to February in the Philippines.

2. Near the Mariana Islands east of Guam. From July to June, 65438+ 10, there were typhoons around the island, and there were few typhoons before May. June and June,11-65438+February, mainly occurred in the waters near the south of the islands.

3. On the sea near Marshall Islands (typhoons are mostly concentrated in the northwest and north of the islands). In June 5438+10 month, 1 month, typhoons occurred most frequently here; There are few typhoons in June.

4. North-central South China Sea. There are the most typhoon opportunities in June-September, with fewer typhoons in April, increasing gradually in May, and decreasing gradually from 10 degrees north latitude to 15 degrees in February, but most of them occur in the North Sea.

How is a typhoon formed?

There are often many weak tropical eddies on the surface of tropical oceans. We call them "embryos" of typhoons, because typhoons always grow from this weak tropical vortex. Through meteorological satellites, it is found that only about 10% of a large number of tropical eddies on the ocean surface can develop into typhoons. How is a typhoon formed?

Generally speaking, the occurrence of typhoons requires the following basic conditions:

1. First of all, there must be a wide enough tropical ocean surface, which requires not only that the surface temperature of seawater is higher than 26.5℃, but also that the water temperature in a layer of seawater 60 meters deep should exceed this value. Among them, the vast ocean surface is the necessary natural environment for the formation of typhoons, because the friction between air molecules in typhoons consumes an average of 365,438+000-4,000 calories/cm **2 of energy every day, and this huge energy can only be supplied by the latent heat released by the vast tropical ocean. In addition, the strong wind around the tropical cyclone will make the sea water churn around the center, even in the typhoon center where the air pressure drops very low, and then spread around, so the sea water will churn around from the typhoon center. In a typhoon, this sea churning phenomenon can affect the depth of 60 meters. On the ocean surface where the seawater temperature is lower than 26.5℃, it is difficult to maintain a typhoon due to insufficient heat energy. In order to ensure that the sea surface temperature is always above 26.5℃ during this tumbling process, this warm water layer must have a thickness of about 60 meters.

2. There must be a weak tropical vortex before the typhoon is formed. We know that the operation of any machine consumes energy, which requires energy. Typhoon is also a "heat engine". It rotates there at such a huge scale and speed and consumes a lot of energy, so it needs an energy source. The typhoon's energy comes from the water vapor in the tropical ocean. In a pre-existing tropical vortex, the air pressure in the vortex is lower than that around it, and the air around it carries a lot of water vapor to the center of the vortex, causing upward movement in the vortex area; Wet air rises and water vapor condenses, releasing huge latent heat of condensation, which can make typhoons run. Therefore, even if there is a tropical ocean surface with high temperature and high humidity to supply water vapor, it is impossible to form a typhoon without the strong rise of air and the condensation and release of latent heat. Therefore, the upward movement of air is an important factor to produce and maintain typhoons. But the necessary condition is that a weak tropical vortex exists first.

3. There should be enough earth rotation deflection force. Because the geostrophic deflection at the equator is zero and gradually increases to the poles, the typhoon is located about 5 latitudes away from the equator. Because of the rotation of the earth, there is a force that changes the direction of air flow, which is called "earth rotation bias force" On the rotating earth, the rotation of the earth makes it difficult for the surrounding air to flow directly into the low pressure, but rotates counterclockwise along the center of the low pressure (in the northern hemisphere).

4. Above weak low pressure, there is little difference between high and low air direction and wind speed. In this case, the upper and lower air columns work together, and the high-altitude heat is easy to accumulate, thus heating up. Once the cyclone is generated, the ambient airflow above the friction layer will flow along the isobar, and the warming effect of the upper layer can be further completed. In the area north of 20 N, the climatic conditions have changed, mainly because the high-rise wind is very strong, which is not conducive to warming, and typhoons are not easy to appear.

These are just the necessary conditions for a typhoon. Having these conditions does not mean that there will be a typhoon. The occurrence of typhoon is a complicated process, which has not been fully understood so far.

In the next section, we will introduce the typhoon structure, related weather, typhoon path, typhoon forecast and typhoon prevention measures in detail.

The Harm and Utilization of Typhoon

When a typhoon moves on the sea, it will set off huge waves, followed by violent storms, which will pose a serious threat to sailing ships. When a typhoon lands, the storm will cause great losses to people's lives and property, especially to agriculture and buildings.

However, typhoons do not always bring misfortune to mankind, except for its "evil" side, and sometimes they also benefit mankind. For some areas, if there is no typhoon, the growth of crops and the bumper harvest of agriculture in these areas are unimaginable. Typhoons in the northwest Pacific, hurricanes in the West Indies and tropical storms in the Indian Ocean account for almost 60% of the total number of strong tropical cyclones in the world, bringing abundant rain to fertile land and creating a suitable climate. Typhoon precipitation is the main source of summer precipitation in Jiangnan area and northeast provinces of China. It was the typhoon that lifted the drought in the Pearl River Delta, the two lakes basin and the Northeast Plain, and ensured a bumper agricultural harvest. It is precisely because of the large amount of precipitation brought by typhoon that many large and small reservoirs are full of rainwater, so that the hydroelectric generating set can operate normally and save raw coal 1 10,000 tons; On a hot day, a typhoon comes, and a cool breeze blows gently, which can also cool off the heat. Therefore, it is not unreasonable for some people to think that the typhoon "caused local disasters and benefited a large area".