How do you judge the gale often mentioned in the weather forecast?

In the Tang Dynasty more than 1000 years ago, our people not only recorded weather phenomena such as rain and snow, but also measured the wind. At the beginning of the Tang dynasty, an accurate instrument for measuring wind speed was not invented, but at that time, the moving speed of wind could be calculated according to the characteristics of wind to objects, and the wind grade could be determined.

There is such a record in Li's "Phenomenon Play Zhan": "The moving leaves are ten miles, the songs are hundred miles, the branches are two hundred miles, the leaves are three hundred miles, the dead branches are four hundred miles, the big branches are five hundred miles, the stones are three thousand miles." This is to estimate the wind speed according to the influence of wind on trees. "moving leaves for ten miles" means that the leaves are slightly fluttering and the wind speed is ten miles a day; What "sings" is the rustling of leaves, and the wind speed at this time is hundreds of miles a day.

In addition, some wind grades are determined according to the symptoms of trees, such as "first-class moving leaves, second-class ringing, third-class shaking branches, fourth-class falling leaves, fifth-class broken branches, sixth-class broken branches, seventh-class broken trees, flying sand and stones, and eighth-class uprooting trees".

These eight winds, plus "no wind" and "gentle wind" (when the wind comes, it is cool and gentle, so it is called gentle wind), which can be combined into ten levels. The grades of these winds are not much different from those imported from abroad. This can be said to be the earliest wind level in the world.

More than 200 years ago, there were no instruments for measuring the magnitude of wind, and there were no unified regulations. Every country expresses itself in its own way. At that time, there was a man named beaufort in England. He carefully observed the situation of various objects on land and at sea in different winds, and accumulated 50 years of experience before he divided the wind into 13 in 1805, which is also commonly known as Beaufort wind scale. Later, after research and supplement, the original explanation was explained more clearly, and the speed of each wind level was increased, which became the "jargon" for forecasting wind power.

Wind has both magnitude and direction, so the wind forecast includes wind speed and direction. The magnitude of wind speed is usually expressed by wind grade. The level of wind is determined according to the degree of influence of wind on ground objects. Meteorology is generally divided into seventeen grades according to the magnitude of wind.

In the weather forecast, we often hear the expression "the north wind is 4 to 5", in which the wind refers to the average wind; If you hear the phrase "gust 7", gust refers to the wind with high and low speed, and the wind at this time refers to the high-speed wind.

In fact, in nature, the wind sometimes exceeds 12. For example, the central wind force of a strong typhoon or tornado may be much larger than the magnitude of 12, but the wind above the magnitude of 12 is rare, so the magnitude is generally not specified.

Hurricane John is the third recorded category 5 hurricane in the Central Pacific Ocean, which set a record for the highest wind speed in this area, reaching 280 km/h. Since 1994, only Hurricane Ou Kai has reached the category 5 hurricane intensity in the Central Pacific Ocean. Like girma, its air pressure is lower than John's, but its wind speed is slower than John's.

When Typhoon Dai Wen transited, its intensity was equivalent to the second-class typhoon in the tropical cyclone classification of the National Hurricane Center. At that time, the average wind force in Victoria Harbour was 1.33 km/h, the highest gust was 259 km/h, and Tate's Cairn also recorded a gust of 284 km/h.

Typhoon Taipei is the strongest tropical cyclone typhoon ever recorded on earth. At present, the tropical cyclone with the highest wind speed is Typhoon Haiyan in the northwest Pacific Ocean, with an average wind speed of 3 15 km/h.

The fastest "normal" wind speed on the earth's surface reached 372km/h, which was recorded on April 1934 in Mount Washington, New Hampshire, USA. However, during the tornado in Oklahoma in May 1999, the fastest wind speed measured by researchers reached 513 km/h. ..

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