This document discusses various aspects of water in the atmosphere and how it relates to meteorology. It covers the water cycle and how water changes state between solid, liquid, and gas through processes like melting, evaporation, condensation, and sublimation. It also defines key humidity terms like relative humidity, saturation, and dew point. Relative humidity depends on both the air temperature and its water vapor content compared to the maximum it can hold at a given temperature.

1. Meteorology
Temperature and humidity

2. Water Vapor
• Source of all condensation and
precipitation
• Most important gas in the atmosphere for
understanding atmospheric processes
• Zero to 4% by volume

3. Water Changes State
• Always requires heat
• Heat is either absorbed or released
• Water must pass through the atmosphere
in the form of water vapor
• If all the water vapor was in a global layer
it would only be 2 mm deep

5. Solid to Liquid
• Melting
– Heat is transferred to ice water
– Temperature of the water remains a constant 0
degrees C until all ice has melted
– Heat breaks apart crystal structure of ice forming
liquid water

7. Liquid to Gas
• Evaporation
– Changing a liquid into a gas
– Requires 2500 joules of energy to convert 1
gram of liquid water to water vapor

8. Liquid to Gas
• “Evaporation as a cooling process”
– Energy is needed to evaporate water
– Cooling effect after getting out of the pool
– Energy needed comes right from your skin
• Condensation
– Water vapor changes to liquid
– Generates clouds and fog

10. Solid to Gas
• Sublimation
– Conversion of solid directly to a gas
– No liquid state
– Dry ice (frozen carbon dioxide)
– Generates “smoke”
• Deposition
– Conversion of vapor directly to a solid
– Frost on cold objects, grass, windows

11. Humidity
• Humidity – the amount of water vapor in the air
• Saturation
– Balance between liquid water and water vapor
– Closed jar: half water, half air
– Water begins to evaporate  increases pressure in
the air
– Pressure is caused by more water vapor molecules
moving into the air
– Pressure in air continues to increase
– Forces more water molecules to return to liquid
– When a balance occurs, air is said to be saturated

12. Saturated Air
• Depends on temperature
• Warm air contains more water vapor than
cold air

13. Relative Humidity
• Ratio of air’s actual water vapor content
compared to the amount of water vapor
the air can hold at the time
• How much water vapor can the air hold?
– Depends on temperature and pressure
• Indicates how near the air is to saturation

16. Relative Humidity
• How can it be changed?
– 1 – adding or removing water vapor
• Occurs naturally
• Oceans and smaller bodies of water
– 2 – varies with temperature
• Lowering air temperatures causes INCREASE
• Raising air temperatures causes DECREASE

17. Dew Point
• The temperature at which one parcel of air
would need to be cooled in order to reach
saturation
• If the air was cooled further it would
condense
• This would cause dew,
fog, clouds

18. How do you measure humidity?
• Hygrometer – used to measure relative
humidity
• Psychrometer
– Two thermometers side by side
– One is dry bulb, the other wet bulb
– Larger the difference on the reading the lower
the relative humidity
– If air is saturated the thermometers will have
the same reading