Atmospheric Moisture

Water in the Atmosphere Water vapor is the source of all condensation and precipitation Essentially all water on Earth is conserved – water cycle

Changes of State Changing states requires energy transfer in the form of heat Latent heat is the stored heat that needs to be added or removed for a phase change to occur

Phase changes requiring…. The addition of heat:  Melting  Evaporation  Sublimation – solid directly to gas The removal of heat  Freezing  Condensation  Deposition – gas directly to solid

Humidity Saturation – the maximum quantity of water vapor air can hold at a given temperature and pressure Warm air can hold more water vapor than cool air

Relative Humidity (RH) Ratio of the air’s actual water vapor content compared with the amount of water air can hold at that temperature and pressure 2 ways to change RH  1. Add or remove water vapor  2. Change the temperature

Relative Humidity (RH) (cont.) Once air is saturated further cooling causes condensation (ex: dew, clouds) Measured using a sling psychrometer

Dew Point Dew Point –Temperature to which air would have to be cooled for saturation to occur Depends on how much moisture is present For every 10 C increase in temp. the amount of water vapor for saturation double  High dew points indicate moist air  Low dew point indicate dry air

Using RH and Dew point Dew point can found by using the RH  When air temp. and dew point are close: RH is high  When air temp. and dew point are far apart: Rh is low

Explain this….. Explain the relationship between saturation, relative humidity and dew point.