The Three Phases of Water

• Vapor - gas (invisible)

• Liquid - droplets (cloud and precipitation)

• Solid - ice crystals (snow, frost)– extraordinary characteristic - exists in all 3

phases at the same time in the free atmosphere– maximum content by % - 3 or 4% in Tropics– many ways to measure (Td, Tw, RH, e/es)

Water Measurements

The Three Phases of Water

• The Relative part of RH– depends on actual water content– depends on air temperature

• in a typical day: RH max when T is minimum

• RH min when T is maximum– provided no change of moisture content

• Dewpoint Temperature– depends only on actual water content

The Water Cycle

The Three Phases of Water

• Making a cloud– Three ingredients

• water vapor (source of water to be evaporated)

• cooling mechanism (lifting by bouyancy or topography)

• condensation nuclei (most common forms are dust and sea salt - hygroscopic)

• Making it rain/snow– Two processes (warm/cold cloud)

Non Precipitating Water

• Dew

• Frost

• Guttation