Title: Moisture in the Atmosphere
1Lecture 5
- Moisture in the Atmosphere
2Water in the Atmosphere
- Water comprises 0-4 of the earths atmosphere
- Water is important to the earths energy budget
because of - Latent heat release
- Greenhouse gas
- Water has a high heat capacity
3Water (H2O)
4Phase Changes that Release Latent Heat
- Condensation
- Vapor gt Liquid
- Freezing
- Liquid gt Solid (Ice)
- Deposition
- Vapor gt Solid (Ice)
5Phase Changes that Absorb Latent Heat
- Evaporation
- Liquid gt Vapor
- Melting
- Solid (Ice) gt Liquid
- Sublimation
- Solid (Ice) gt Vapor
6Phase Changes
- If you leave a glass of water sitting out for
many days, what happens to the water level in the
glass? - .does it go up?
- ..does it go down?
- ..does it remain constant?
7Phase Changes
- What happens if you cover a glass of water with
plastic wrap and let it sit out for many days? - .does the water level go up?
- .does it go down?
- .does it stay the same?
When evaporation balances condensation.. the
air is said to be saturated with water vapor.
8What determines the rate of evaporation?
- Wind
- Temperature of the Water
What determines the rate of condensation?
9Hydrologic Cycle
Some vapor condenses into clouds, and then falls
as precipitation
Wind transports water vapor to other regions
Water evaporates back into vapor
Precipitation lands on ground and in water ways.
Water evaporates from oceans
Water runs off land into oceans
10Hydrologic Cycle
Precipitation lands on ground and in water ways.
Some vapor condenses into clouds, and then falls
as precipitation
Water evaporates back into vapor
Wind transports water vapor to other regions
Water runs off land into oceans
Water evaporates from oceans
11Hydrologic Cycle (Frozen)
Precipitation lands on Polar Ice Cap.
Some vapor condenses into clouds, and then falls
as precipitation (Snow!)
Ice/Snow sublimates into the air
Wind transports water vapor to other regions
Ice flows off the polar plateaus, onto the ice
shelves, melts into oceans or Icebergs calve and
melt into the oceans.
Water evaporates from oceans
12True or False
- ___Warmer air holds more water vapor than cold
air. - ___Humid air weighs more than dry air.
13Water Vapor is a Gas in the Atmosphere, just like
Nitrogen and Oxygen
14Weight of Dry Air
- Oxygen (O2)
- Molecular weight 32
- by volume 21
- 32 x .21 6.72
- Nitrogen (N2)
- Molecular weight 28
- by volume 78
- 28 x .78 21.84
- Dry air
- Molecular weight 21.84 6.72 28.56
15Weight of Moist Air
- Water Vapor (H2O)
- Molecular weight 18
- by volume 4
- 18 x .04 .72
- Dry Air
- Molecular weight 28.56
- by volume 95
- 28.56 x .95 27.132
- Moist Air
- Molecular weight 27.132 .72 27.852
Moist air weighs less!!!!
16How can we measure water vapor in our atmosphere?
Handout
17Measures of Moisture
- Absolute measure
- Mixing Ratio (w)
- Vapor Pressure (e)
- Absolute Humidity
- Specific Humidity
-
- Dew Point Temperature (Td)
- Relative measure
- Relative Humidity (RH)
- Dew Point Depression (Tdd)
- Capacity/Limit
- Saturation Vapor Pressure (es)
- Saturation Mixing Ratio (ws)
- Temperature (T)
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19Vapor Pressure
20Relative Humidity
- The relative humidity can be changed by two
methods - Change the airs water vapor content
- Change the temperature
- Relative humidity does NOT give you an idea of
the actual amount of water vapor in the air.
21Moisture/Temperature During the Day
22Relative Humidity
Mixing Ratio
Vapor Pressure
- RH (w/ws ) x 100
- (e/es) x 100
- Example w 5 g/Kg, ws 13 g/Kg
- RH 38
- Example e 12 mb, es 48mb
- RH 25
23Which has drier air?
- The Sahara Desert
- Air temp 35 oC
- Dew point 5 oC
- Relative humidity 16
The Sahara has more water vapor!
- Antarctica
- Air Temp -2 oC
- Dew Point -2 oC
- Relative humidity 100
24Relative Humidity vs. Specific Humidity
25What is the relative humidity in your home like?
- Do you think it is greater or less than that of a
desert? - Where does the air in our homes come from?
26Moisture Variables
- Absolute measures depend only on the moisture
content - Relative measures depend on both the water
content and the temperature
27Relating Variables
28What does it mean when people say that the
weather in Arizona isnt bad because it is a dry
heat?
29Humidity and People
- Evaporation is a cooling process for human skin.
- The less humid the air is, the easier it is for
sweat to evaporate. - The skin can become as cool as the wet bulb
temperature.(Tw)
30Heat Index
- This index is used by the National Weather
Service. - Combines ambient temperature with relative
humidity. - Determines an apparent air temperature, or what
the temperature feels like to the average
person. - A comfort index much like Wind Chill
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32Why does naturally curly hair get frizzy when
it is humid, and straight hair goes limp?
33Measuring Humidity
- Hygrometers measure humidity.
- Hair Hygrometer
- Electric Hygrometer
- Infrared Hygrometer
- Dew Cell
- Dew Point Hygrometer
- Sling Psychrometer
Blonde Hair 1 Sensor of Humidity