| A | B |
|---|
| atmosphere | The layer of air that surrounds our planet |
| air pressure | Particles of air pressing down on the Earth's surface |
| troposphere | The layer of atmosphere closest to Earth |
| stratosphere | The layer of atmosphere that contains ozone |
| greenhouse effect | The warming of Earth caused by the atmosphere trapping thermal energy from the sun |
| air mass | A huge body of air which all has similar temperature and moisture |
| front | The border where two air masses meet |
| cirrus | Wispy, high-altitude clouds that are made up of ice crystals |
| cumulus | Puffy cotton-ball clouds that begin to form when water droplets condense at middle altitudes |
| cumulonimbus | Towering, dark rain clouds with a nimbus of gray white |
| stratus | Dark gray clouds that form a low layer and sometimes bring light rain or snow showers |
| barometer | An instrument that measures air pressure |
| humidity | The amount of water vapor in the air |
| hygrometer | A tool to measure the moisture in the air |
