| A | B |
|---|
| Water cycle | Continual movement of water among Earth's atmosphere, oceans, and land surface through evaporation, condensation, and precipitation. |
| Evaporation | Process by which molecules at the surface of a liquid absorb enough energy to change to a gas. |
| Condensation | The change in state from a gas to a liquid. |
| Humidity | The amount of water vapor in a given volume of air. |
| Relative humidity | Percentage of water vapor in the air compared to the maximum amount of water vapor that air can contain at a particular temperature. |
| Psychrometer | Instrument used to measure relative humidity. |
| Dew point | Temperature at which condensation begins. |
| Cirrus | Wispy, feathery clouds made of ice crystals that form at high levels. |
| Cumulus | Fluffy, white clouds, usually with flat bottoms, that look like rounded piles of cotton. |
| Stratus | Clouds that form in flat layers and often cover much of the sky. |
| Precipitation | Any form of water that falls from clouds and reaches Earth's surface as rain, snow, sleet, or hail. |
| Rain gauge | Instrument used to measure precipitation. |
| Drought | Long period of low precipitation. |
| Air mass | Huge body of air that has similar temperature, humidity, and air pressure at any given height. |
| Front | The boundary where unlike air masses meet but do not mix. |
| Cyclone | A swirling center of low air pressure. |
| Anticyclone | A high-pressure center of dry air. |
| Isobar | A line on a weather map that joins places that have the same air pressure. |
| Isotherm | A line on a weather map that joins places that have the same temperature. |
| Jet stream | Bands of high-speed winds about 10 kilometers above Earth's surface. |
