Atmospheric Moisture

Water in the AtmosphereWater vapor is the source of all condensation and precipitation

Essentially all water on Earth is conserved – water cycle

Changes of StateChanging 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:

MeltingEvaporationSublimation – solid directly to gas

The removal of heatFreezingCondensationDeposition – 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 RH1. Add or remove water vapor2. Change the temperature

Relative Humidity (RH) (cont.)

Once air is saturated further cooling causes condensation (ex: dew, clouds)

Measured using a sling psychrometer

Dew PointDew Point –Temperature to which air

would have to be cooled for saturation to occur

Depends on how much moisture is presentFor every 10 C increase in temp. the

amount of water vapor for saturation doubleHigh dew points indicate moist airLow dew point indicate dry air

Using RH and Dew point

Dew point can found by using the RHWhen air temp. and dew point are

close: RH is highWhen air temp. and dew point are

far apart: Rh is low

Explain this…..

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