How a cloud forms
1 min 30 s. The words are spoken and shown in the picture; the player can also show them as subtitles.
For the Earth and Space Sciences Regents. Topic: Structure of the lower atmosphere, with the past questions on it.
What Dr. Mars says (the words of the video)
How does a cloud form?
The Sun warms the ground; the ground warms the air above it.
Warm air near the ground rises.
Dr. Mars stands on a parcel of air, a mass of air that moves together.
His thermometer shows the temperature of the air.
The air holds water vapor: water as an invisible gas.
Here it is drawn as faint white curved lines.
Higher up, air pressure is lower, so the rising parcel expands.
Expanding air cools: Dr. Mars's thermometer reading falls.
At its dew point, water vapor condenses into tiny droplets.
Dew point: the temperature at which water vapor starts to form droplets.
The parcel turns white: it is now a cloud.
Cloud base: the height where rising air reaches its dew point.
Check yourself! Where does the cloud start to form: A, B, or C?
Compare each air temperature with the dew point.
Answer: C! The air there has cooled to its dew point.
When his parcel rose to the height of C, his thermometer read the dew point.
Dr. Mars. Free practice for the New York Earth and Space Sciences Regents.