Water in the Atmosphere Chapter 16.4

Humidity A measure of the amount of water vapor in the air How much water vapor air holds depends on temperature Warm air holds more water vapor than cold air

Relative Humidity The amount of water vapor in the air compared to the maximum amount of water vapor air can hold at a particular temperature Blue = amount of water in the air Yellow = amount of water air can actually hold

Measuring Relative Humidity R.H. can be measured with a psychrometer

To find relative humidity: Look across from dry-bulb temp Look down from difference between dry-bulb and wet-bulb temp (dry-wet = difference) Result is relative humidity

Cloud Formation Clouds form when water vapor in the air condenses to form liquid water or ice crystals Dew point – the temperature at which condensation begins Clouds need particles on which to condense (salt, dust, or smoke) Dew or frost is when water vapor condenses on a surface

Clouds Cumulus – fluffy, rounded Cirrus - feathery Nimbus added to cloud type indicates precipitation Stratus – flat layers

Cloud Combinations Altocumulus – high puffy Altostratus- high layered Cirrocumulus - fish scales Predicts rain Cumulonimbus – often Produce thunderstorms

Let’s Make A Cloud

Precipitation Any form of water that falls from clouds and reaches the surface Rain – water droplet at least 0.5 mm in diameter Sleet – rain that falls through a freezing layer of air and falls to the ground Freezing rain – rain that freezes after hitting the surface

Precipitation Snow – water vapor that freezes directly into ice crystals and stays solid all the way to surface Hail – droplet of water that freezes high in a cloud, falls and gathers more moisture in the cloud and is forced upward in the cloud by updrafts to freeze. Falls to ground when it becomes too heavy.