What is the principle of micrometeorology?

Micrometeorology is a discipline that studies atmospheric phenomena and processes near the ground with the horizontal scale below12000m. Sometimes refers to meteorology in the atmospheric boundary layer. Micro-meteorology refers to the small-scale climate characteristics in the near-surface atmosphere and the upper soil caused by some structural characteristics of the underlying surface. This small-scale climate feature is generally manifested in individual meteorological values and sometimes in individual weather phenomena (such as wind, fog, frost, rain, etc.). However, the change of this factor will not greatly change the weather and climate characteristics determined by large-scale processes (advection and front). Phenomenon in daily life How can the "micrometeorology" tofu, which is hidden in the frozen tofu bubble, "freeze"? It turns out that "craftsman" is "ice". Ice crystals have the characteristics of unusual "merging" effect and "abnormal expansion" on water droplets. When the temperature drops below 0℃, a small amount of water in tofu first forms ice crystals around the "frozen core" in tofu. At this time, tofu has three "phases": ice, water and gas. Because ice crystals are solid, once they are formed, their molecular movements are not as free as liquid water. Compared with the surrounding supercooled water with the same temperature (that is, water that does not freeze below 0℃), they are already in a supersaturated state. On the contrary, ice crystals will become "obese" because of the constant condensation of water vapor on their surfaces (that is, directly changing from gas to solid). Under the constant "merging" of ice crystals, the water in tofu gradually disappears because of this "merging" or partial evaporation. Under the "abnormal expansion" of ice, the plastids containing tofu also expand correspondingly, which increases the gap between plastids. Because the water vapor pressure of air is smaller than that of tofu, it is constantly evaporated and consumed at high wind speed, and what is preserved is "dry matter". This is the "micrometeorology" of water in the phase evolution. The evolution and interaction of the "three-phase state" mentioned above have occurred countless times in nature. Generally speaking, precipitation occurs in the clouds, but it doesn't always happen when there are clouds, because there are countless cloud droplets floating in the air, which are so small that we can't see them with naked eyes, and the diameter is less than1%mm. The condensation of water vapor occurs on very tiny condensation nuclei such as salt particles, dust or soot with strong hygroscopicity. When the air relative humidity is close to 100%, even if the temperature is far below the freezing point, small water droplets can be formed. However, to reach the size of raindrops with a diameter of one millimeter, the diameter of some cloud drops must be increased by a hundred times. Ice crystals can also form on frozen nuclei, which come from some soil dust particles or meteorite dust. Because the number of frozen nuclei is far less than that of condensed nuclei, water droplets may not freeze at a low temperature of MINUS 40℃ and become supercooled. When ice crystals enter supercooled clouds and supercooled water droplets, the phenomenon that ice crystals "merge" is similar to supercooled water droplets in frozen tofu bubbles. At this time, if the actual vapor pressure of air is between the saturated vapor pressure of ice crystals and water droplets, ice crystals are supersaturated and water droplets are unsaturated. Therefore, supercooled water droplets will evaporate, and water vapor will condense on ice crystals and become "prisoners" of ice crystals. This kind of "ice crystal effect", in which water droplets are constantly evaporating and getting smaller, and ice crystals are constantly "merging" to make water vapor bigger, is of great significance for ice crystals to become big cloud droplets in mixed clouds as soon as possible and promote precipitation. Because after the cloud droplets increase, whether the updraft makes them rise or the downdraft makes them fall, more small cloud droplets can be "merged" or "collided", and finally become liquid or solid precipitation and land on the ground when the updraft can't support it. Based on the principle of "ice crystal effect" in precipitation, artificial freezing nuclei (silver iodide, etc.) are introduced into artificial precipitation enhancement operations in various places. Shoot anti-aircraft guns or rockets into the clouds, so that the supercooled clouds become ice crystal clouds. When the ice crystals "collide" up and down until the updraft can't hold up, they melt into showers when they fall.