Look at the clouds and know the weather.

Visible polymer suspended in the atmosphere, consisting of a large number of tiny water droplets or ice crystals. Generally, it doesn't touch the ground. If it touches the ground, it's called fog. Because the atmospheric pressure decreases with the increase of height, the air will expand and cool when it rises, and the saturated water vapor pressure will also decrease. When the water vapor in the air reaches saturation and condenses into a large number of tiny water droplets, clouds will form. Clouds with temperatures below 0℃ are often composed of small water droplets (supercooled water droplets) and ice crystals. The appearance of clouds is varied, and its changes often reflect the structure of the atmosphere and the evolution of weather, such as the vertical temperature of the atmosphere, cloudy, sunny and cloudy weather conditions such as rainstorm, hail, tornado and typhoon. Cloud precipitation is an important water source to sustain life. The movement of clouds can indicate the direction and speed of air flow. The cover of clouds affects the radiation of the sun to the ground, thus affecting the climate and the growth of crops. The refraction and scattering of solar light by clouds and precipitation will form colorful atmospheric light images such as halo, China, rainbow, neon and Emei Baoguang. Sometimes violent discharge occurs between clouds, leading to lightning and lightning strikes. People often predict the weather changes in local areas according to the appearance of clouds and their photoelectric phenomena.

As early as the beginning of19th century, L Howard of Britain divided clouds into different types according to their appearance. Up to now, the name of cloud proposed by him has been adopted in meteorological observation. As for the microscopic nature of the cloud, it was determined by observing it with a microscope at the end of 19. With the development of science and technology, people use balloons and airplanes to directly observe its microstructure, use radar to observe its macro-evolution, and use satellite images to understand the distribution and evolution of cloud systems around the world, which makes their understanding of clouds more and more comprehensive and in-depth.

Classification of Clouds In meteorological observation, according to the height and shape of clouds, clouds can be divided into four categories: high clouds, middle clouds, low clouds and straight clouds, and ten genera: cirrus, cirrocumulus, cirrostratus, high cumulus, high stratus, stratus, nimbostratus, cumulus and cumulonimbus. In cloud and precipitation physics, clouds are classified according to physical characteristics: ① according to dynamic characteristics. The vertically developing clouds formed by air convection are called convective clouds or cumulus clouds; When a large range of air gathers and rises slowly, a horizontally extending and evenly layered cloud is formed, which is called layered cloud. ② Classification according to temperature characteristics. Clouds with a temperature higher than 0℃ are called warm clouds. Clouds with temperatures below 0℃ are called Leng Yun. ③ Classification by microstructure. Clouds composed entirely of water droplets are called water clouds; A cloud composed entirely of ice crystals is called ice cloud; Clouds composed of water droplets and ice crystals are called mixed clouds.

The size of water droplets (cloud droplets) in the microstructure of clouds is different, and their radii range from a few microns to 100 microns. The distribution of cloud droplet number per unit volume with cloud droplet size is called cloud droplet spectrum. The total number of cloud droplets per unit volume, called cloud droplet concentration, is generally101~103/cm3. In the continental air mass, the average radius of cloud droplets is small and the concentration is large; In the ocean air mass, the average radius of cloud droplets is large and the concentration is small. There are also water droplets with a radius greater than 100 micron in the cloud, which are actually raindrops that have not fallen off from the cloud. As for the shapes of ice crystals, snow crystals and other solid particles in the cloud, they change with different growth conditions. The concentration of ice crystals in clouds ranges from less than one per liter to several hundred per liter.

The total amount of water contained in water droplets or ice crystals per unit volume of the cloud is called the water content of the cloud, which is generally10-1~100g/m3. The water content varies greatly with the type, development stage and location of the cloud. The water content of pure ice crystal clouds can be less than 10- 1g/m3, and the water content of cumulonimbus clouds can reach100-1g/m3.

Knowledge of the cloud

Content: Cloud.

It refers to a large-scale cloud area existing in tropical areas, and its diameter is about 4 latitudes or more, which is called a cloud cluster. This is a tropical weather system. Many tropical weather systems, such as intertropical convergence zone and tropical storms, are composed of or developed by tropical clouds. Clouds can generally be divided into:

In general, the horizontal range of clouds is 2- 12 latitude. A cloud consists of many cumulonimbus clouds, with cirrus complexes and popcorn clouds at the top, and the area is less than 10 square centimeter. Clouds are composed of several cumulonimbus clouds. This kind of cloud often appears in Tibet and South America? From June to September, there are seasonal storms in Southeast Asia and its adjacent waters. With the advance of monsoon, the cloud explosively develops northward. At 10-20 north latitude and 70- 100 east longitude, it is often covered by seasonal clouds of 1-2, making it the largest cloud cluster on the earth. The north-south width varies from several latitudes to 10 latitudes. The east-west length can reach 20-40 radial degrees, which is closely related to the southwest monsoon activity, so it is called monsoon cloud cluster. Clouds often cause heavy rain.

Cloud chamber/expansion chamber/fog chamber

A box-type device that can control air pressure, temperature and humidity to form clouds is called a cloud chamber. This is a laboratory device for cloud precipitation physics. As far as the temperature of cloud formation is concerned, cloud chamber can be divided into warm cloud chamber (cloud temperature is higher than 0℃) and Leng Yun chamber (cloud temperature is lower than 0℃). As far as cloud-making methods are concerned, they can be generally divided into expansion type, diffusion type, constant temperature type and mixed cloud chamber type. Cloud room generally consists of a main box and a set of auxiliary equipment. The main box can be cylindrical, hexahedron, cuboid, etc. Made of copper or stainless steel, or made of plastic or plexiglass. Auxiliary equipment often includes refrigeration, cloud making, catalysis, observation and other systems. Some cloud rooms can also control airflow and are equipped with wind tunnels. The size of the cloud chamber varies greatly. The largest cloud chamber has a volume of more than 3,000 cubic meters, and the smallest cloud chamber has a volume of only tens of cubic centimeters. Cloud chamber is often used to simulate and study the generation, growth and transformation of cloud and precipitation particles and their accompanying photoelectric phenomena under different conditions, detect the concentration of cloud nuclei and ice nuclei, and test the properties of artificial ice nuclei and hygroscopic nuclei. There are many ways to generate clouds in the cloud chamber: ① Adiabatic expansion and cooling make water vapor saturated and condense into cloud droplets; (2) The Leng Yun chamber wall descends, which leads to the decrease of humidity in the cloud chamber, reaching saturation and condensation of cloud droplets; (3) directly spraying tiny water droplets into the cloud chamber to form a cloud; (4) The cloud chamber is supersaturated to produce condensation.

Cold cloud precipitation mechanism

Leng Yun refers to a cloud whose upper temperature is lower than 0℃ and whose lower temperature can still be higher than 0℃. The upper part of the cloud is often an ice mass, and there are supercooled water droplets and water vapor. How did Leng Yun grow up in a short time and cause rain or snowfall and hail? Its theoretical basis is bergeron process: in the cloud area where the temperature is below 0℃ and there are supercooled water droplets, ice crystals and water vapor, the saturated water vapor pressure on the ice surface is low and the water surface is high, so that when the water vapor pressure in the cloud is between the ice surface and the water surface saturation value, the water vapor condenses on the ice crystals to make the ice crystals bigger, and the water droplets will continue to evaporate and become smaller or disappear, forming ice crystals to "capture".

When the updraft with water vapor, cloud droplets (water droplets) and ice cores reaches the upper part of the cloud with the temperature below 0℃, the water vapor condenses on the ice cores and grows into ice crystals, and the water droplets become supercooled water droplets. Under the storage of ice crystals, supercooled water droplets and water vapor, the ice crystals continuously capture the moisture of water vapor and water droplets through Bergeron process and grow into larger ice crystals. Under the action of updraft and gravity, ice crystals keep rising and falling, and grow through the processes of collision, adhesion and merging with supercooled water droplets, thus producing a large number of large ice crystals (called snow crystals) with line length exceeding 200 microns in a few minutes, and then falling off from the cloud bottom. If the temperature of the gas layer is high, it will melt and form rainfall; If the temperature below 0℃, it will not melt and cause snowfall, and often 20-30 snow crystals stick together to form snowflakes. If the updraft of the cloud is very strong, the cloud is extremely developed, and the water droplets are too cold, the ice mass may collide to form a large hail block and drop the hail to the ground.

Warm cloud precipitation mechanism

There is a popular saying that when the updraft carries cloud condensation nuclei and water vapor to a certain height, and the air is close to saturation or supersaturation, water vapor condenses on the condensation nuclei, producing cloud droplet embryos, and continues to rise and condense to grow into cloud droplets. Some larger cloud droplets will collide with many smaller cloud droplets in the process of rising or falling, which is called collision growth. They can grow into raindrops with a radius of 200 microns or even several millimeters. Raindrops with a radius of more than 3 mm will be seriously deformed in the process of falling, and sometimes they will break into several small raindrops. However, such small raindrops may be picked up by the updraft and grow into large raindrops along the collision path. The chain reaction process of rising, growing, falling, breaking, rising again and growing again is called Langmuir chain reaction, which makes warm clouds grow into raindrops with sufficient quantity and quality in a few minutes. When the updraft and the atmosphere can't,

Characteristics of various clouds on satellite cloud images

A cirrus cloud on the visible light cloud image has a low albedo and is gray-dark gray; If cirrus clouds in visible light cloud images are white, their clouds are thick or overlap with other clouds; On the infrared cloud picture, cloud top temperature is very low and white. Whether it is visible light or infrared cloud image, cirrus cloud has fiber structure.

B. Medium clouds (high-level clouds and cumulus clouds) On the satellite cloud image, the medium clouds are connected with the weather system, showing a wide range of bands, eddies and commas. On the visible light cloud map, the middle cloud is gray-white to white, and the thickness of the cloud is determined by the different tones; On the infrared cloud image, the middle cloud is moderately gray.

C. Cumulonimbus clouds are the whitest whether they are visible light or infrared cloud images; When the high-altitude wind is small, the cumulonimbus cloud is round, and when the high-altitude wind is strong, there is often a cirrus anvil at the top, which is oval.

D. Cumulus clouds and cumulus clouds are very white in visible light, but due to the different heights of cumulus clouds, the colors on infrared clouds can range from gray to white, with uneven texture and irregular boundaries. Its patterns are cumulus lines and perforated clouds.

E stratocumulus (fog) on the visible light cloud map, stratocumulus (fog) appears as a smooth and uniform cloud area; The hue is white to off-white. If the thickness of stratus cloud exceeds 300 meters, its hue is very white. Stratocumulus (fog) boundary is neat and clear, consistent with the trend of mountains, rivers and coastlines. On the infrared cloud image, the tone of stratocumulus is dark, which is similar to that of the ground.

Cloud identification standard of satellite cloud image

There are six criteria for identifying clouds on satellite images:

(1) Structure type: refers to the distribution pattern of image points with different light and dark degrees, such as high-level cumulus clouds which are often banded and vortex-shaped, and an open cellular cloud system composed of cumulus clouds. ;

(2) Range refers to the distribution scale of cloud systems, from which the physical process of cloud formation can be inferred. Small-scale cloud systems are often related to small and medium-scale weather systems; Large-scale is related to large-scale weather systems.

③ Boundary shape: Different types of clouds have different boundaries, such as irregular cumulus boundary and regular stratocumulus (fog) boundary.

④ Tone: refers to the brightness of an object. The hue of the cloud on the visible cloud image is related to the thickness and composition of the cloud, while on the infrared cloud image it is related to the cloud top temperature.

⑤ Shadow: refers to the high cloud projected on the low target at a certain solar altitude angle.

⑥ Texture: It is used to indicate the roughness of the cloud top surface, for example, the cloud top surface of stratus (fog) is even and smooth; However, the surface of cumulus clouds is uneven.