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Charge accumulation in cold clouds Charge accumulation in warm clouds

The condition for thunder and lightning is that there is a lightning strike in the thunderstorm cloud and form a polarity.Scientists have conducted a lot of observations and experiments on the charging mechanism of thunderclouds and the regular distribution of charges, accumulated a lot of data, and put forward various explanations, but some arguments are still controversial.The “ion current” hypothesis in the initial stage of convective cloud is that there are a large number of positive and negative ions in the atmosphere. On the raindrops in the cloud, the charge distribution is uneven. The outermost molecules are negatively charged, and the inner layer is positively charged. The potential difference of the layer is about 0.25V higher than that of the outer layer.In order to balance this potential difference, the water droplets must preferentially absorb the negative ions in the atmosphere, which makes the water droplets gradually become negatively charged.When the development of convection begins, lighter positive ions are gradually brought to the upper part of the cloud by the rising airflow; while the negatively charged cloud droplets are heavier and stay in the lower part, causing the separation of positive and negative charges.Charge accumulation in cold clouds When convection reaches a certain stage and the cloud body rises to a height above 0°C, there will be supercooled water droplets, chalcedony and ice crystals in the cloud.This kind of cloud that is composed of water vapor condensate in different phases and whose temperature is lower than 0°C is called cold cloud.The charge formation and accumulation processes of cold clouds are as follows: ① The supercooled water droplets collide and freeze on the chalcedony grains. There are many water droplets in the cloud that will not freeze when the temperature is lower than 0℃. This kind of water droplets are called supercooled water droplets.Supercooled water droplets are unstable, as long as they are gently shaken, they immediately freeze into ice particles.When the supercooled water droplets collide with the chalazion, they will freeze immediately, which is called crash freezing.When a crash occurs, the outside of the supercooled water droplet immediately freezes into an ice crust, but its inside remains temporarily liquid, and because the latent heat released by the external freezing is transferred to the inside, the temperature of the liquid supercooled water inside is higher than that of the outside ice crust. .The difference in temperature causes the frozen supercooled water droplets to be positively charged on the outside and negatively charged on the inside.When the inside also freezes, the cloud droplet expands and splits, and the outer skin ruptures into many positively charged ice chips, which fly to the upper part of the cloud with the airflow. The core part of the negatively charged frozen droplet attaches to the heavier chalazion, making the chalazion. It is negatively charged and stays in the middle and lower part of the cloud.

② The frictional collision between ice crystals and chalazion is electrified chalazion is composed of frozen water droplets, white or milky white, and the structure is relatively crisp.Since cold water droplets often collide with it and release latent heat, its temperature is generally higher than that of ice crystals.There are a certain amount of free ions (OH- and H+) in ice crystals, and the number of ions increases with increasing temperature.Because there is a temperature difference between the contact part of the chalazion and the ice crystal, there must be more free ions at the high temperature end than at the low temperature end, so the ions must migrate from the high temperature end to the low temperature end.During ion migration, the positively charged hydrogen ions are faster, while the negatively charged heavier hydroxide ions are slower.Therefore, an excess of hydrogen ions at the cold end occurred within a certain period of time, resulting in an electric polarization in which the high temperature end was negative and the low temperature end was positive.When ice crystals come into contact with the chalazion and separate again, the higher temperature of the chalazion will be negatively charged, while the lower temperature of the ice crystal will be positively charged.Under the action of gravity and updraft, the lighter, positively charged ice crystals are concentrated on the upper part of the cloud, and the heavier negatively charged chalazion stays in the lower part of the cloud, thus causing the upper part of the cold cloud to be positively charged and the lower part to be charged. Negative electricity.③ In addition to the two electrification mechanisms of the cold cloud mentioned above, the water droplets are electrified due to the thin salt content. Some people have also proposed the electrification mechanism due to the thin salt content of the water droplets in the atmosphere.When cloud droplets freeze, the ice crystal lattice can hold negative chloride ions, but repel positive sodium ions.Therefore, the frozen part of the water droplet is negatively charged, while the unfrozen part is positively charged (when the water droplet freezes, it goes from the inside to the outside).As the water droplets freeze in the process of falling, they fall off the surface water before they can freeze, forming many small positively charged cloud droplets, while the frozen core part is negatively charged.Due to the sorting effect of gravity and airflow, the positively charged droplets are brought to the upper part of the cloud, while the negatively charged chalazion stays in the middle and lower part of the cloud.The charge of warm clouds accumulates in tropical areas, and some clouds are located in areas above 0°C throughout the cloud.Therefore, it contains only water droplets and no solid water particles.This kind of cloud is called warm cloud or water cloud.Thunder and lightning can also occur in warm clouds.In thunderstorm clouds in mid-latitudes, the part where the cloud body is located below the 0℃ isotherm is the warm area of ​​the cloud.An electrification process also occurs in the warm area of ​​the cloud.During the development of Lei Yuyun, the above-mentioned mechanisms worked separately at different stages of development.However, the most important charging mechanism is still caused by the freezing of water droplets.A large number of observational facts show that only when the cloud top presents a fibrous filamentous structure, the cloud develops into a thundercloud.Aircraft observations found that there are a large number of cloud particles dominated by ice, snow crystals, and chalazion in thunderclouds, and the accumulation of a large amount of electric charge is the electrification mechanism of the thunderstorm cloud, which can only happen by relying on the collision, freezing and friction during the growth of chalazion.