When ice crystals grow and stick together, they combine to form larger flakes.
This process is a key step in the formation of snowflakes and subsequent precipitation. The provided reference details the progression after this initial aggregation:
- The ice crystals combine to form larger flakes.
- These larger flakes then attract more supercooled droplets. Supercooled droplets are water droplets that remain liquid even at temperatures below 0°C (32°F).
- This growth process continues, causing the flakes to become larger and heavier.
- Eventually, the flakes become heavy enough to fall back towards the ground.
- As they fall through warmer layers of air, these ice particles can melt to form raindrops.
The Journey from Crystal to Precipitation
The transformation of tiny ice crystals into substantial snowflakes, and potentially raindrops, involves several stages:
- Nucleation: Ice crystals form on microscopic particles in very cold clouds.
- Growth: These crystals grow as water vapor freezes onto them.
- Aggregation: Ice crystals collide and stick together, forming larger flakes. This is the process described in the question.
- Accretion (Riming): The flakes may also collide with supercooled water droplets, which freeze upon impact, causing the flakes to grow further and become denser.
- Falling: Once the flakes are large and heavy enough, they fall towards the ground.
- Melting (Optional): If the falling ice particles pass through a layer of air that is above freezing, they will melt and reach the ground as rain.
Why This Process Matters
The sticking together of ice crystals (aggregation) is essential because individual ice crystals are often too small and light to fall to the earth as precipitation. Aggregation creates particles large enough to overcome air resistance and descend as snow. The subsequent interaction with supercooled droplets and melting determine whether the precipitation arrives as snow, rain, or other forms like sleet or freezing rain.
This entire sequence highlights the dynamic nature of cloud physics and how subtle changes in atmospheric conditions dictate the type of weather we experience on the ground.
