Precipitation, such as rain or snow, falls in small, individual units rather than large units due to the processes involved in cloud formation and the physics of atmospheric conditions. The size and structure of precipitation particles are determined by the processes of condensation, coalescence, and collision within clouds. Here's a brief explanation:
Cloud formation: Clouds are formed when warm, moist air rises and cools, causing water vapor to condense into tiny water droplets or ice crystals. These tiny droplets or crystals are initially very small, typically on the order of micrometers in size.
Coalescence and collision: Within the cloud, these tiny droplets or ice crystals can collide and coalesce with other droplets or crystals. As they collide, they grow in size through a process known as coalescence. However, collisions and coalescence tend to occur between similar-sized particles, leading to gradual growth rather than sudden formation of large units.
Air resistance and updrafts: As precipitation particles grow in size, they become subject to air resistance. Larger particles experience greater resistance and are more likely to be slowed down or pushed upward by updrafts in the cloud, preventing them from growing excessively large.
Terminal velocity: Terminal velocity is the maximum speed a particle can attain while falling through the atmosphere. As precipitation particles grow larger, they reach a size where the upward force of air resistance equals the downward force of gravity, causing them to fall at a constant speed. The terminal velocity of larger particles is higher, making it difficult for them to continue growing significantly before they reach the ground.
Due to these processes, precipitation particles tend to grow gradually and remain relatively small before they reach the ground. Raindrops, for instance, typically range in size from 0.1 to 5 millimeters in diameter. Similarly, snowflakes form from ice crystals that aggregate in a complex process, resulting in intricate and unique shapes but still relatively small in size.
It's worth noting that under certain atmospheric conditions, such as severe storms or updrafts in thunderstorms, it is possible for larger and more intense precipitation units, like hailstones, to form. However, these conditions are relatively rare and not the norm for most instances of precipitation.