How is the lowest black cloud in the sky formed?

Clouds are no strangers to us. White in sunny days and black in rainy days are called clouds. They make the sky unpredictable. People often see that the sky is sometimes blue and cloudless, sometimes white clouds are blooming, and sometimes dark clouds are gathering. Why sometimes there are clouds in the sky and sometimes there are no clouds? How are clouds formed? What is it made of? Clouds floating in the sky are composed of many tiny water droplets or ice crystals, some of which are mixed together. Sometimes it also contains some big raindrops and ice particles. The bottom of the cloud does not touch the ground and has a certain thickness. The formation of clouds is mainly caused by water vapor condensation. More than ten kilometers from the ground, the closer to the ground, the higher the temperature and the denser the air; The higher the altitude, the lower the temperature and the thinner the air. On the other hand, the water surface of rivers, lakes and seas, as well as the moisture of soil, animals and plants, evaporate into the air at any time and become water vapor. After water vapor enters the atmosphere, it turns into clouds to cause rainfall, or condenses into frost dew, and then returns to the ground, permeates the soil or flows into rivers, lakes and seas. Later evaporation (sublimation) condensation (condensation) drops. It goes on and on. After the water vapor enters the lower atmosphere from the evaporation surface, the temperature here is high and there is much water vapor. If the hot and humid air is lifted, the temperature will gradually decrease, and when it reaches a certain height, the water vapor in the air will reach saturation. If the air continues to be lifted, there will be excess water vapor. If the temperature there is higher than 0℃, the excess water vapor will condense into small water droplets; If the temperature is lower than 0℃, excess water vapor will condense into small ice crystals. When these small water droplets and small ice crystals gradually increase to a level that can be recognized by human eyes, it is a cloud. People often see that the sky is sometimes blue and cloudless, sometimes white clouds are blooming, and sometimes dark clouds are gathering. Why sometimes there are clouds in the sky and sometimes there are no clouds? How are clouds formed? What is it made of? Clouds floating in the sky are made up of many tiny water droplets or ice crystals, some of which are mixed together. Sometimes it also contains some big raindrops and ice particles. The bottom of the cloud does not touch the ground and has a certain thickness. Thunderstorm clouds People usually refer to the clouds where lightning occurs as thunderclouds. In fact, there are several kinds of clouds related to lightning, such as stratocumulus, nimbostratus, cumulonimbus, cumulonimbus, and the most important one is cumulonimbus. Lei Yun in general professional books refers to cumulonimbus clouds. The process of cloud formation is a process in which water vapor in the air reaches saturation or supersaturation through various reasons and condenses. Water vapor saturation in the air is a necessary condition for cloud formation. The main ways are: (1) keeping the water vapor content unchanged and cooling the air; (2) keeping the temperature constant and increasing the water vapor content; (3) Not only the water vapor content is increased, but also the temperature is reduced. But for the formation of clouds, the cooling process is the most important process. In the process of cooling, the cooling effect brought by ascending movement is the most common. Cumulonimbus cloud is a kind of cloud formed in the process of strong vertical convection. Because the ground absorbs much more solar radiation heat than the air layer, the ground temperature rises more during the day, especially in summer. Therefore, due to heat conduction and heat radiation, the atmospheric temperature near the ground rises, the gas temperature inevitably expands, the density decreases, and the pressure also decreases. According to the principle of mechanics, it will rise, and the density of the air layer above it is relatively high, and it will sink. In the rising process, the hot airflow expands and depressurizes, and at the same time, it exchanges heat with the high-altitude low-temperature air, so the water vapor in the rising air mass condenses, and water droplets appear, forming clouds. In the process of strong convection, the fog droplets in the cloud further cool down and become supercooled water droplets, ice crystals or snowflakes, and gradually increase with the height. At the freezing height (-10℃), due to the latent heat released by the freezing of supercooled water, the cloud top suddenly develops upward and spreads horizontally near the tropopause, forming a cloud anvil, which is a remarkable feature of cumulonimbus clouds. In the process of cumulonimbus cloud formation, positive and negative charges are accumulated in different parts of the cloud under the simultaneous action of atmospheric electric field, temperature difference electrification effect and debris electrification effect. When the charge accumulates to a certain extent, it will discharge between clouds or between clouds and the ground, which is what people usually call "lightning". Lightning has brought great disasters to human society with its great destructive power, especially in recent years, lightning disasters have occurred frequently, and the harm to the national economy has become increasingly serious. It is necessary to strengthen the awareness of lightning protection, actively cooperate with meteorological departments, do a good job of prevention, and minimize the losses caused by lightning. Classification of the causes of clouds Clouds are formed in areas where moist air rises and meets cold air. It may happen that the warm air mass in front of the front cloud rises to a cloud topography cloud. When the air rises along the normal terrain, the advection cloud passes through the cold underlying surface, such as the cold water body, which is caused by the convective movement of the air. Cyclone clouds are caused by the rising airflow from the cyclone center. In short, there are three main forms of clouds: large cumulus clouds, large stratus clouds and fibrous cirrus clouds. The scientific classification of clouds was first proposed by French naturalist Jean Lamarck in 180 1. 1929, according to the classification made by British scientist luke howard in 1803, the international meteorological organization divided clouds into ten major cloud genera according to their shapes, components and formation reasons. These ten cloud genera can be divided into three cloud systems according to the height of cloud bottom: high cloud system, middle cloud system and low cloud system. Another classification separates cumulonimbus and cumulonimbus from the low cloud family, which is called the straight cloud family. The cloud base height used here is only applicable to mid-latitude areas. (In addition to Britain and the United States, countries such as the World Gas Organization generally adopt the international system of units. Cirrus (Ci), Cirrocumulus (Cc) and cirrostratus (Cs, cirrostratus) high clouds are formed in the cooler part of the troposphere above 6000m above sea level. It belongs to three genera, all cirrus. At this height, water will solidify and crystallize, so this group of clouds is all made up of ice crystals. High clouds are generally fibrous, thin and mostly transparent. The middle clouds of Ac (altocumulus) and As (stratocumulus) are formed at an altitude of 2,500 to 6,000 meters. They are made up of excessively frozen water droplets. Nimbostratus (Ns) stratocumulus (Sc) stratocumulus (St) low cloud is formed in the atmosphere below 2500m. These include thick and gloomy stratocumulus, stratocumulus (discontinuous stratocumulus) and thick and gloomy nimbostratus. Stratospheric grounding is called fog. Cumulus (Cu, Cumulus) Cumulonimbus (Cb, Cumulonimbus) Straight clouds have a very strong updraft, so they can grow from the bottom to a higher place. Cumulonimbus clouds of rainstorms and thunderstorms can start at a height close to the ground and then develop to a height of 75,000 feet. At the bottom of the cumulonimbus cloud, when the falling cold air meets the rising warm air, it will form a breast-like cloud like a pouch. When the cumulonimbus cloud expands, it will form a thin dome-shaped cloud at the top. Other condensation trails refer to slender clouds formed when jets pass high in the sky. Noctilucent clouds are very rare. They are formed in the middle layer of the atmosphere and can only be seen at high latitudes. Clouds and Weather People have long recognized that weather changes can be predicted by observing clouds. 1802, British naturalist luke howard put forward the famous classification of clouds, which made it more accurate to observe clouds and measure weather. Howard divided clouds into three categories: cumulus, stratus and cirrus. These three types of clouds, together with the words for height and rainfall, produce ten basic types of clouds. According to these cloud phases, people have some reliable experience in forecasting the weather changes in the future 12 hours. For example, if the fluffy cumulus clouds are very scattered, it can be said that it is good weather, but if the clouds expand or have new development, it means that there will be a sudden rainstorm. Clouds and climate clouds absorb heat from the ground and reflect it back to the ground, which helps to keep the earth warm. However, clouds also reflect sunlight directly back into space, which has a cooling effect. Which effect is dominant depends on the shape and location of the cloud.