This blog post explains the various meteorological processes and scientific principles behind the formation of rain and snow in an easy-to-understand manner.
How exactly is precipitation like rain or snow formed? Clouds consist of tiny water droplets or small ice crystals suspended in the air, formed when water vapor in the air condenses. Precipitation is created when these water droplets or ice crystals undergo a growth process within the cloud.
The cloud formation process begins when water vapor in the atmosphere condenses or sublimates. At this stage, cloud particles are very small, with diameters around 0.01mm, making them resistant to evaporation. As cloud particles collide and merge, gradually growing larger, they eventually fall to the ground as precipitation. The form of precipitation is determined by various meteorological conditions, including temperature, air currents, and atmospheric pressure. In temperate or polar regions, precipitation forms as ice crystals grow larger. When the temperature within a cloud ranges from 0°C to -40°C, supercooled water droplets and ice crystals coexist within the cloud. Supercooled water droplets refer to small water droplets in the atmosphere that remain liquid and do not freeze even at temperatures below 0°C. However, below 0°C, the saturation vapor pressure for supercooled water droplets is greater than that for ice crystals. Consequently, supercooled water droplets evaporate into water vapor, which then moves toward the ice crystals. This migrating vapor adheres to the ice crystals, causing them to gradually grow larger. This process is called the ‘nucleation process’. When these enlarged ice crystals fall to the ground, they become snow. If they melt during descent, they become rain. The nucleation process is also applied to create artificial rainfall. Spraying silver iodide into clouds aids in the formation of ice crystals. These formed ice crystals then undergo the nucleation process, growing to become either snow or rain.
Meanwhile, in tropical regions where the temperature inside clouds is above 0°C, ice crystals do not exist. Therefore, precipitation in these areas forms through processes different from the nucleation process. Clouds contain water droplets of various sizes; relatively large droplets collide with and merge with smaller droplets as they fall. At this point, updrafts within the cloud allow the larger droplets to remain in the cloud longer, causing them to repeatedly collide with smaller droplets. The resulting larger droplets then fall, colliding and merging with other droplets in a repeated process. This process is called the ‘collision-coalescence process’. When millions of water droplets merge through collision-coalescence, they form raindrops that fall to the ground. The collision-coalescence process is also applied artificially to induce precipitation. This is done by spraying substances that absorb moisture from the air, such as salt particles, or water droplets into the atmosphere, causing water droplets within clouds to grow larger.
Precipitation plays a crucial role in the Earth’s water cycle. It maintains moisture on the Earth’s surface, which is essential for balancing ecosystems. Furthermore, precipitation replenishes groundwater resources, provides water for agriculture and industry, and plays a major role in preventing natural disasters. For example, rain washes away atmospheric dust and pollutants, improving air quality, and adequate rainfall helps alleviate droughts. Conversely, excessive precipitation can cause flooding, necessitating proper forecasting and management.
Thus, precipitation forms through various meteorological conditions and processes, significantly impacting our lives and environment. Scientists study these processes to enhance the accuracy of weather forecasting, advance artificial rainfall technology, and contribute to preventing natural disasters. Understanding the formation of precipitation and its effects is crucial for responding to climate change and managing the environment sustainably.
