Chapter 17 Moisture, Clouds, Precipitation

Water vapor

• Odorless, colorless gas

• Freely mixes with other gases

• Can change from one state of matter to another

Waters changes of states

Ice, liquid water, water vapor

Calorie

Amount of energy required to raise 1 gram of water 1 degree Celsius

Latent Heat

Energy absorbed or released during a change of state

Mixing ratio

Mass of water vapor in a unit of air compared to remaining mass of dry air

Relative humidity

• Ratio of the air’s actual water vapor content to its water vapor capacity (at a given temperature and pressure)

• Adding or removing water vapor

• Varies with temperature

Dew point temperature

Temperature to which air has to be cooled in order to reach saturation and then begin to condense

Adiabatic Temp changes

Cooling or warming of air caused when it expands/compresses, not because heat is added/subtracted

- Parcel – few hundred cubic meters, independent of surrounds

• Dry: rate of cooling/warming in unsaturated air

• 1°C per 100 meters

• Wet: rate of temperature change in saturated air

Orographic lifting

Air forced to rise over a mountain or barrier

Frontal lifting

Warmer, less-dense air forced over cooler, denser air

Convergence

Pileup of horizontal airflow resulting in upward movement

Localized convection lifting

Unequal surface heating causes localized pockets of air to rise due to buoyancy

Stable air

air that resists vertical displacement

Unstable air

air that does not resist vertical displacement

Cloud condensation nuclei

microscopic particles that serve as surfaces on which water vapor condenses

Hygroscopic nuclei

those that have a high affinity for water, such as salt particles; will absorb water

Clouds

visible aggregates of minute droplets of water or tiny crystals of ice

Cloud types

How precipitation forms

Cloud droplet grow to larger precipitation