Water in the Atmosphere

•          Humidity

–        The measure of the amount of water vapor in the air.

•          Relative Humidity

–        The percentage of water vapor in the air compared to the maximum amount the air could hold.

–        When relative humidity is high, evaporation slows down.

•          Measuring Relative Humidity

–        Psychrometer

•          Uses a wet bulb and dry bulb thermometer

•          Because the wet bulb thermometer is cooled by evaporation, its reading drops below that of the dry-bulb thermometer.

•          How Clouds Form

–        Clouds form through condensation, when water vapor in the air becomes liquid water or ice crystals.

–        Dew Point: The temperature at which condensation forms.

•          Warm air containing water vapor cools, forcing some of the water out of the air and forming water droplets.

•          Particles must be present for condensation to form.

•          Types of Clouds

–        Classified by type and altitude

–        3 main types

•          Cumulus

•          Stratus

•          Cirrus

–        Cumulus

–        Means “heap” or “mass”

–        Indicates fair weather

–        Look like fluffy piles of cotton

•          Stratus

–        Strato means “spread out”

–        Usually cover all or most of the sky

•          Stratus

–        Strato means “spread out”

–        Usually cover all or most of the sky

–        May thicken to form precipitation (nimbostratus)

•          Cirrus

–        Form only at high altitudes (+6 Km)

–        Made of ice crystals

•          Naming clouds

–        May be based on height

–        2 to 6 km above surface = alto meaning “high”

Clouds close to the ground are called fog.