Water and Atmospheric Moisture

1
Water and Atmospheric Moisture
2
(No Transcript)
3
Hydrologic Cycle
4
(No Transcript)
5
Moisture, Clouds, and Precipitation

• Humidity
• Global Precipitation
• Lifting Mechanisms
• Precipitation Processes
• Big Question What Causes Air to Precipitate?

6
Global Precipitation
7
U.S. Current Relative Humidityclick on map
8

• ABSOLUTE HUMIDITY
• Absolute humidity (expressed as grams of water
  vapor per cubic meter volume of air) is a measure
  of the actual amount of water vapor (moisture) in
  the air, regardless of the air's temperature. The
  higher the amount (weight) of water vapor per
  kilogram, the higher the absolute humidity.
• RELATIVE HUMIDITY
• Relative humidity (RH) (expressed as a percent)
  also measures water vapor, but RELATIVE to the
  temperature of the air.
• In other words, it is a measure of the actual
  amount of water vapor in the air compared to the
  total amount of vapor that can exist in the air
  at its current temperature.
• WARM AIR CAN HOLD MORE WATER VAPOR THAN COLD
  AIR, so with the same amount of absolute/specific
  humidity, cooler air will have a HIGHER relative
  humidity, and warmer air a LOWER relative
  humidity.

9
Humidity

• Capacity of air is primarily a function of
  temperature
• Relative Humidity (RH)
• (actual water vapor content)
  x 100 (max. water vapor
  capacity of the air)
• Heated air becomes lower in RH because
  denominator gets larger
• Cooled air becomes higher in RH

10
Saturation vsAir Temperature
The actual amount of Water air can hold
changes With air temperature Air at 104 F can
hold 3 times As much water as 68 F air ! (47
grams vs only 15 grams) Air at 68 F can hold 4
times As much water as air at 0 F (15 grams vs
only 4 grams)
104 F
47 grams
68 F
15 grams
32 F
4 grams
11
Saturation and Dew Point

• Saturated v. unsaturated air
• Dew-point temperature
• temperature to which air must be cooled to reach
  saturation (100 RH)
• water on outside of drinking glass
• ice on your car window
• dew and fog

12
Adiabatic Cooling Clouds and Lifting
Condensation Level (LCL)

• LCL / Cloud base dew point altitude

13
Relative Humidity and Temp.

• RH fluctuates over a day or season.

14
Measuring Relative Humidity

• Sling psychrometer

Hair hygrometer
15
After Saturation Occurs the AirMust Release
Extra Water as Fluid
Water forms on the outside of a cold glass as the
cold Air surrounding the glass chills the air to
the Dew
Point Temperature
The
resulting water
is not from the glass,

the water is from
condensation of

moisture in the air
around the glass


16
In Nature Extra Moisture isTransformed to Water
Droplets
Cold air next to the rain-soaked cliff is chilled
To The Dew Point Temperature creates a Misty
Cloud along a Rocky Mountain slope Air near
the Slope is 100 Saturated
17
(No Transcript)
18
Fog by the Golden Gate
19
Temperature Inversions
Common Summer Inversion in Los Angeles
20
(No Transcript)
21
Which of the four types is this?
Clarence River, Australia
22
Fog A Cloud on the Ground
This April fog occurred in the San Fernando
Valley after a clear, cold April night. It
evaporated by noon.
Fog in Glendale
23
Temperature Inversions
When warmer air overlies cooler air, pollutants
and fog are trapped beneath the inversion.
Common Winter Radiation Inversion in Valleys
24
Which of the four types is this?
25
Which of the four types is this?
Appalachian Mountains
26
An often very dense type of valley fog called
Tule Fog in the Central Valley of California
Pacific Ocean
27
Atmospheric Lifting Mechanisms

• Air Lifting processes create clouds
  precipitation
• Are the only means of precipitation on Earth
• Four types of lifting are recognized
• Convectional Lifting
• Convergence
• Orographic Lifting
• Frontal Lifting

28
Global Precipitation Patterns
29
Convergence
Convergence occurs when large air masses meet
are forced to rise vertically by crowding of
molecules. This process is best seen at the ITCZ
where the Trades Winds meet rise to form
towering clouds heavy precipitation
30
Convectional Lifting
Anywhere air is warmer than its surrounding air,
it will rise. In this example an island heats
more than the surrounding water and causes a
massive cumulus cloud to form.
31
Convectional Lifting Over Florida
Warmer temperatures over the peninsula of
Florida, which is land, cause air to rise
compared to the cooler oceans nearby
Rising air in this Shuttle Picture is Shown by a
Cloud pattern which generally follows the shape
of the southern Florida peninsula
32
Convectional Lifting in the Desert
Extremely high afternoon temperatures in late
summer often leads to thunderstorms throughout
the worlds arid regions.
Mojave Desert
The Grand Canyon in August
33
Orographic Lifting of Air
When air moving Horizontally Encounters
a Mountain it must Rise over the crest As it
rises, it cools To create clouds, And most
often precipitation
Moisture Lost
Dry Air
Moist Air
Run off NO Run off
34
Frontal Lifting of Air
Although not a mountain range, masses of moving
air Create the same effect Unlike mountains air
masses Can provide lifting in many different
locations Fronts can lift air Which is
stable, Creating clouds large amounts Of
precipitation As rain, snow, Sleet or hail
35
Precipitation Types / Properties
36
Snowflakes and Temperature
Snow crystal images from an electron microscope
37
Seasonal and Global Variation in Lifting
Mechanisms and Precipitation

• Convergence increases when subsolar point
  (ITCZ) is in the region.
• Convection maximized when insolation and
  temperature are most intense and when marine air
  moves over warm land masses common also in
  deserts, with their intense summer heating
• Orographic requires forced upslope rising of
  air (mountains)
• Frontal midlatitudes only, where cold and warm
  air meet and collide

38
Summary

• Humidity
• Relative Humidity
• Relationship to Temperature
• Dew Point
• LCL/Cloud Base
• Precipitation (Rain, Snow, Sleet)
• When air is substantially cooled below the dew
  point, large droplets or ice crystals form and
  may fall if large enough.
• Lifting Mechanisms
• Convective, Orographic, Frontal, Convergence