Lecture 11 Clouds Part 2 Flashcards
Why do some clouds cause precipitation?
Because cloud droplets must grow big enough to fall as precipitation
How do cloud droplets grow to the raindrop size?
- condensational growth
- collision coalescence
Collision and coalescence process
A) collisions that join together small cloud droplets
B) coalescence that attaches with faster and larger droplets with smaller slower droplets
How do cloud droplets grow to the raindrop size?
Bergeron process
Accretion
Aggregation
Supercool water
Is water at or below 0 degrees Celsius but remains liquid
(It remains liquid because there are not suitable particles for ice to nucleate upon. The nucleation particles are called ice nuclei.
Bergeron process
In a cloud that has both ice crystals and water droplets, the ice crystal will grow larger at the expense of surrounding water droplets
What causes the Bergeron process?
1) air is saturated in clouds, so both the liquid droplet and ice crystal are in equilibrium
2) at the same sub freezing temperature, molecules escape the surface of water much more easily than they escape the surface of ice
3) the saturation vapor pressure just above the water surface is greater than the saturation vapor pressure above the ice surface
Accretion
A process that ice crystal growth by sweeping up supercooled water drops
Aggregation
The process by which ice crystal collide and form a single larger ice particle
Forms of precipitation
1) rain
2) snow
3) sleet and freezing rain
4) graupel and hail
Virga
Observable streak or shift of precipitation that falls from a cloud but evaporates before reaching the ground
Graupel
Precipitation that forms when supercooled water droplets in the air are collected and freeze on falling snowflakes forming balls of crisp opaque rime
How do we measure precipitation
- rain gauges
- weather radar
- satellite
