What is weather observation?

Tracking the weather is sometimes as simple as observing the wind direction, but sometimes it is as complicated as launching a satellite worth hundreds of millions of yuan. Meteorological monitoring still depends on some basic measurement methods-observation of temperature, humidity, wind and air pressure. For centuries, these have been part of the work of meteorologists. It is still very complicated to estimate these weather characteristics, but their variables are consistent. In recent decades, these standard observation data collected in the field can be completed by a variety of remote sensing instruments. Radar, satellites and other equipment can now report weather conditions more than ten miles, hundreds of miles or even thousands of miles away.

In the past, mercury thermometers or alcohol thermometers were used to measure temperature, but at the beginning of17th century, the first thermometers used were air and alcohol. The atmosphere gets hot, the liquid expands and the liquid level in the thermometer rises. Nowadays, digital thermometers rely on internal changes in the electronic characteristics of circuits or resistors. Most weather stations publish records of the highest or lowest temperature every 24 hours, mainly according to the actual temperature changes. The United States uses Fahrenheit, while other regions use Celsius.

Meteorologists use barometers to measure atmospheric pressure, which is the force per unit area formed by the atmospheric mass above the earth's gravitational pull-down instrument. A typical aneroid barometer measures the pressure directly acting on an empty pipe with a certain degree of vacuum. At present, the more advanced barometer is called piezoelectric resistance meter, which measures the change of the reaction force of the atmosphere on the silicon film. A weather station located at an altitude of 1 mile (1.6 km) can withstand about 85% of the atmospheric pressure at sea level. This is because the air above it is thin. In order to get rid of the influence of this altitude, barometer is often read as altitude. This transformation assumes a hypothetical but reasonable standard atmosphere between the actual height and sea level.

Air pressure used to be measured in inches of mercury. For a mercury barometer, liquid can rise in a vacuum tube because atmospheric pressure acts around the mercury tube. The standard atmospheric pressure at sea level is 29.92 inches of mercury, or the metric conversion is about 1.0 13 millibar (if water is added to the classical barometer instead of mercury, the instrument needs to extend to the height of three floors). The humidity in the air is measured by a hygrometer. It is a hygrometer that stretches or contracts with hair, dry rope or thin metal wire according to the change of relative humidity.

Another wet method is to use dry and wet bulb thermometer to measure dew point temperature. Wind direction is the main meteorological variable. Use it as a sign of the coming weather and record it. Some records about wind direction can be traced back to more than 2000 years ago. The horizontal wind direction can be recorded with a compass scale, with 360 representing the north, 90 representing the east,180 representing the south and 270 representing the west. Record or describe the wind direction with an approximate decimal system. If the east wind turns to the southeast wind or the northwest wind.

Wind speed is usually measured by an anemometer. Open your arms against the wind with propellers and things like that, and install countless spinning balls. The pressure anemometer can accurately record the dynamic pressure generated at the open end due to the action of wind. Acoustic anemometer measures wind power by measuring the sound generated by wind blowing through the gap between two sensors. The recording unit of wind speed is miles per hour, also called knots, which is another name for miles per hour, equivalent to 1. 15 miles per hour. The metric system adopts kilometer/hour or meter/second. Since the wind speed changes every second, modern anemometers include a software that can measure the average constant wind speed and the power of strong winds in a specific time. Monitor the wind at high altitude with radio sonar and wind direction profile monitor.

Combined with other factors used to predict meteorological changes, weather phenomena include visibility (within a few miles or kilometers), cloud shape and height, and the proportion of gathering in the sky. The previous wind, the rainfall in a certain period of time. Finally, it includes the thickness of snowfall and the amount of water contained in the snow.

The Global Meteorological Observatory conducts ground observation at least once an hour and sends the observation results to the meteorological department of the country where it is located.

Most of these readings were processed and made public within a few minutes. This is due to international cooperation and the Internet. In addition, volunteer observers also control nearly 10,000 weather stations, and each person makes one or two observations every day. The observation report, together with international data, laid the foundation for climate observation.

In the past few years, many countries, including Japan and the United States, have fully or mostly automated ground observation websites. In this way, observers only check and maintain these websites. These websites are equipped with the most advanced electronic equipment, and the observation results can often be transmitted once in 10 ~ 15 minutes.

Before the invention of weather balloons, people's observation of atmospheric motion was only related to the ground. Since the19th century, balloon experiments have been used to obtain the atmospheric motion above the ground, and these heights of airflow play a key role in the weather movement and change.

The radio came out in the 1920s. It was not until the advent of radiosondes that stations with weather balloons changed people's views on the upper atmosphere. The most typical example is that radiosonde measures air pressure through a small barometer, and measures the influence of temperature and humidity on electrical conductivity. With the rise of radiosonde, it sends back reports by radio, and measures wind speed and direction according to the changes of radiosonde in a certain area. About an hour later, a special radiosonde rose 15 miles (24 kilometers). The balloon inflated and finally exploded. The instrument package has completed its task and landed on the ground with a micro parachute.

In the 1940s, radiosondes spread information to the whole world every day. Meteorologists will soon study high-altitude jets and other features. At present, 1000 radiosondes are launched every day in the world, most of which are in the northern hemisphere.

Radar is the best tracker, which can track the wind during a thunderstorm. You can also draw a salty map of the rain and snow area. The first radar was developed and improved during World War II, and later became a civilian radar. Radar sends out electromagnetic signals, usually microwaves, which will turn back when encountering raindrops, hail and snowflakes; By measuring the time required for the signal to return to the radar and how many signals return, scientists can calculate how far the precipitation area is and how much precipitation there is.

Doppler radar was widely used in 1990s. It uses the frequency of the return signal to estimate the moving speed of precipitation targets-to estimate the speed at which the wind blows them.

In North America, Europe and Australia, people often collect information from clouds to ground lightning. They are used to distinguish and track storms and forest fires, and also used in aviation and other fields. There are about 100 sets of radar antenna networks on the American meteorological website to detect the angle or arrival time of cloud-to-ground pulse signals, and there are more than 20 million such effects every year. The idea of going from the earth to space for the first time changed people's understanding of their homes, triggered global environmental changes and changed meteorology. The photos taken by the rocket show that the global cloud network is more complicated than people expected. Scientists began to imagine an orbiting satellite, which can monitor the earth at all times. By the mid-1960s, their dreams had come true. Satellites take pictures of the earth and send back information in a few minutes.

There are basically two kinds of meteorological satellites: geostationary satellites, that is, geostationary operational environment satellites, referred to as GDES；; Polar orbit satellite is a polar control environment satellite, referred to as POES. In the geostationary orbit, the geostationary satellite is located about 22,000 miles (35,000 kilometers) above the equator, and its running speed is synchronized with the earth's rotation speed, and it hangs in one place almost day and night. The rest of the earth is monitored by polar orbiting satellites, which travel repeatedly from north to south and pass near the polar regions every two hours.

Satellite pictures of TV weather broadcasts are usually taken by geosynchronous satellites. Although they can be seen in the daytime, they are usually developed by infrared rays. Infrared rays diffused from the earth's surface can be used to estimate water vapor in the air. This is because when the wavelength of infrared reaches 6.7 microns, water vapor can easily absorb energy. The more water vapor there is, the more infrared rays from the earth will be absorbed before reaching the satellite. Infrared emission can also be used to measure the temperature of cloud top, which is closely related to storms.

Microwave data has many special functions. Because microwaves can penetrate clouds, there is less energy loss. For example, the appearance of ice and snow passing through the planet can be tracked because the microwave frequency of frozen water is different from that of land and liquid water.

The life span of a satellite is only a few years-this gives scientists a chance to launch a new satellite. After the development of the past 20 years, mankind has a broader understanding of the atmosphere. According to the amount of ultraviolet radiation reflected from the stratosphere to the polar orbiting satellites above it, the annual increase and decrease of the Antarctic "ozone hole" are monitored. The United States launched a detector in 1995 to monitor the lightning inside the clouds and from the clouds to the ground. The measurement results show that lightning is less than half of what scientists expected. Some satellites even carry radar equipment into space. These devices measure the height of the ocean surface (the index of water temperature) and the storm surge of the ocean (the wind speed guide on the sea surface).

People often observe the weather, but the global weather map is only arranged twice a day, that is, 0000 UTC and1200 UTC-a globally recognized 24-hour system. Radiosondes have also been launched, and a full set of external observations have been completed. All the major weather stations in the world use these data. The chart shows the wind force on different isobaric surfaces (such as 850, 700 and 500 mbar), and also shows that the temperature, humidity and air pressure recorded by radiosonde are relatively high. It is necessary to check these data in detail, because once they enter the computer prediction system, even a few wrong observations will cause serious losses. Use specially designed software to find out the corresponding observation values in the general meteorological map. A similar method can adjust the data to fit the map grid. These grids are used in the model to infer future weather conditions from the current weather. The data measured by radiosonde are marked with punctuation marks on the chart, which is called thermal detection. Each detection shows a follow-up survey of temperature and humidity from the ground to the top of the troposphere over the designated place. Next to the detection is an arrow, which indicates the wind direction and wind speed at each altitude, and the mark is the same as that in the horizontal weather map. Detection can be used to calculate rainfall and humidity, the energy of storm formation, the rotation of thunderstorm and the possibility of tornado formation.

Most foreign-made satellites are used for research, not for weather forecasting. Satellites measure the temperature at different heights in the atmosphere to make up for the deficiency of the global radio detection network. This situation is normal in the ocean and southern hemisphere, because there are too few radio detection networks there.