in the weather forecast issued by meteorological stations, we often hear the saying that the wind turns north to south, and the wind force is 2 to 3. The "level" here indicates the wind speed.
wind speed is the forward speed of the wind. The greater the air pressure difference between two adjacent places, the faster the air flow, the greater the wind speed, and the greater the strength of the wind. Therefore, the size of the wind is usually expressed by the wind force. The unit of wind speed is expressed in meters per second or kilometers per hour. When releasing the weather forecast, most of them use the wind level.
how is the wind power series determined?
more than a thousand years ago, in the Tang dynasty, people not only recorded weather phenomena such as sunny, rainy and snowy weather, but also measured the wind power. 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 the wind could be calculated and the wind grade could be determined according to the characteristics of the wind to objects. There is such a record in Li Chunfeng's "Phenomenon Play Zhan": "Moving leaves are ten miles, singing songs are hundred miles, shaking branches are two hundred miles, falling leaves are three hundred miles, twigs are four hundred miles, big branches are five hundred miles, stones are thousands of miles, and big roots are three thousand miles." This is to estimate the speed of the wind according to the effect of the wind on the trees. "Moving leaves for ten miles" means that the leaves are slightly fluttering, and the speed of the wind is ten miles a day; "Singing" 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 singing, third-class shaking branches, fourth-class falling leaves, fifth-class broken branchlets, sixth-class broken branches, seventh-class broken trees, flying sand and stones, and eighth-class uprooting trees and roots". These eight levels of wind, plus two levels of "no wind" and "gentle wind" (when the wind comes, it is cool and gentle, and the dust can't afford it, 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 2 years ago, there was still no instrument for measuring the magnitude of wind power, and there was no unified regulation. Every country expressed it 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 sea in different winds, and accumulated 5 years of experience before dividing the winds into 13 grades in 185. 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 now. In some places, the content of wind power level has been compiled into ballads for memory:
on the zero-level windless kitchen smoke; The first-class soft wind smoke is slightly inclined;
the secondary breeze leaves ring; Three-level breeze swaying branches;
level 4, wind and dust; Five-level breeze water waves;
a strong wind of level 6 shakes the tree; Seven-level wind walk is difficult;
the branches of the eight-level gale are broken; Nine-level gale chimney destroyed;
ten-level gale roots are uprooted; Eleven storm lands are rare;
category 12 hurricanes are extremely rough.
the distance that the wind moves per second-the wind speed, its formula is "from all the way to nine, multiply by two". It means: from level 1 to level 9 wind, multiply each level by 2, and the maximum speed of the wind can be roughly obtained. For example, the maximum speed of the first-class wind is 2m per second, the second-class wind is 4m per second, and the third-class wind is 6m per second, and so on. There are also transitional figures between winds at all levels, such as the first wind is 1-2 meters per second, the second wind is 2-4 meters per second, the third wind is 4-6 meters per second, and so on. Below is a wind scale.
wind grade table
wind grade sea level wave height (m) sea surface and fishing boat sign land surface object sign equivalent wind speed (m/s)
generally the median in the highest range *
--. ~ .2
1.1.1 with microwave smoke to indicate the wind direction, The leaves shake slightly for .3 ~ 1.51 < P > 2.2.3 with small ripples. When the fishing boat shakes the human face, it feels windy, the leaves make a slight noise, the flag begins to flutter, the tall grass and crops begin to shake for 1.6 ~ 3.32 < P > 3.61. with small waves, and the fishing boat gradually feels that the leaves and twigs shake endlessly, and the flag unfolds. The tall grass and crops keep shaking 3.4 ~ 5.44
4 1.1.5. When the fishing boat is full of sails, it can make the hull lean to one side and blow up dust and paper on the ground, and the branches shake. The tall grass and crops fluctuate 5.5 ~ 7.97
5 2.2.5. There are more white foams on the top of the waves, and some leaves and twigs of the fishing boat swing away from the sails, and there are small waves on the inland water surface. The waves of tall grass and crops fluctuated obviously 8. ~ 1.79
63.4. White foam began to be blown away from the wave top by the wind, and most branches of fishing boats were shaken, and wires whirred, making it difficult to hold umbrellas. Tall grass and crops fell to the ground from time to time 1.8 ~ 13.812
74.5.5 White foam left the wave top and was blown into stripes, and the whole tree was shaken, and the big branches were shaken. It is inconvenient to walk in the windward. 13.9 ~ 17.1 16
8 5.5 7.5 White foam is blown into obvious stripes to destroy twigs, and people feel great resistance when they walk in the windward. 17.2 ~ 2.7 19
9 7. 1. The waves blown by the wind reduce the horizontal visibility, make it difficult for motor boats to sail, damage the straw houses and lift the tiles. Big branches can be broken 2.8 ~ 24.4 23
1 9. 12.5 The horizontal visibility is obviously reduced by the waves blown by the wind, and the sailing of motor boats is dangerous. Trees can be blown down, and general buildings are damaged 24.5 ~ 28.4 26
11.5 16. The horizontal visibility is obviously reduced by the waves blown by the wind, and the extremely dangerous trees encountered by motor boats can be blown, and general buildings are seriously damaged 28. 32.6 > 31
Actually, in nature, the wind sometimes exceeds 12. For example, the wind force in the center of a strong typhoon or a tornado may be much larger than the magnitude of 12, but the gale above 12 is relatively rare, so the magnitude is generally not specified.
In order to measure the wind more accurately, people often use portable anemometers to measure the wind in the field. This kind of portable anemometer generally consists of a sensing part and a counter (see the left figure). The induction part consists of three air cups (there are also four air cups) mounted on the cross, and the air cups can rotate freely on bearings, and the air cups are protected by a small frame. The lower part of the central shaft is connected with the counter, and the air cup rotates, which also makes the counter rotate. So the counter records the number of revolutions of the air cup. A counter usually has two or three counting disks, with the large pointer indicating single digits and ten digits, and the hands on the two small counting disks indicating hundred digits and single digits respectively. There is a switch (starting lever) at the lower part of the instrument. Pushing it up can make the counter engage with the sensing part and the counter starts to work. When the starting lever is pulled down, the counter is separated from the sensing part and the counter stops working. When the instrument is placed in a high place and it is inconvenient to start it directly by hand, a small rope can be used to connect the switch. When observing, the rope can be pulled to open and close. Portable anemometers are generally placed in places with open surroundings and no tall obstacles, and their bodies are vertical. Turn off the switch before observation and write down the indicator of the pointer. After a minute or two, turn on the switch and start the stopwatch to record the time. At this point, the observer quickly left the anemometer and stood downwind of the instrument. Nearly 1 seconds after starting the instrument, the observer quickly approached the instrument, turned off the switch at the positive 1 seconds, and recorded the second pointer indication. According to the two readings before and after, the difference is calculated, which indicates the scale number of the anemometer pointer during the observation time and is recorded in the record table. Divide this difference by the observation time, and you can get the scale number of the anemometer every second, and take one decimal place. Then according to the number of scales per second, find out the average wind speed (unit: m/s) from the verification certificate of the anemometer, and take one decimal place.
it is best to observe it twice in a row and take its average value to eliminate the instrument itself and human error.
some portable anemometers not only have the structural performance of the anemometer mentioned above, but also have a wind vane on the shaft to indicate the wind direction, which is called a anemometer.