Title Photo Page

1
Title Photo Page
6Atmospheric Moisture
2
Impact of Moisture on the Landscape

• Atmospheric moisture influences landscape both in
  short term and long term.
• Short term, with puddles, flooding, snow and ice
• Long term, with precipitation integral to
  weathering and erosion, critical to vegetation.

• Precipitation
• Floods
• Snow and ice
• Wind
• Erosion
• Weathering
• Precipitation and phase changes
• Winds
• Atmospheric Particles

• Terrestrial Vegetation
• Types and distribution of biota
• Natural Resource
• Water for human consumption
• Energy
• Storage and transfer

3
The Nature of Water Common place but Unique

• Water is both the most distinctive and the most
  abundant substance on Earth.
• Surface water makes up more than 70 of Earths
  surface.

4
The Nature of Water Common place but Unique

• Occurs in three forms in the atmosphere
• Ice
• Liquid
• Water vapor

• Fig. 6.1

5

• 1 Water Molecule
• H2O

• Covalent bond
• Fig. 6-2

• Hydrogen bond
• Fig. 6-3

6

• Properties of Water
• Changes State
• Liquid
• Solid
• Vapor
• Expands Upon Freezing
• Important in weathering of rock
• Basis of shelf ice and icebergs
• Adhesion (Sticky)
• Surface tension
• Capillary action

• Fig. 6-4

7
Water facts

• As water freezes it contracts until it reaches
  about 4C and then expands as it cools from 4C
  to 0C.
• hexagonal structures (as water freezes)
• ice floats (less dense than water)
• Water is a universal solvent
• it can dissolve almost anything
• Water also has a great heat capacity.
• when warmed, it can absorb an enormous amount of
  energy with only a small increase in temperature
• high heat capacity is attributed the great amount
  of energy required to overcome the hydrogen bonds
  between water molecules

8
Phase Changes of Water

• Evaporation liquid water converted to the
  gaseous form.
• Condensation water vapor converted to the
  liquid form.
• Sublimationthe process by which water vapor is
  converted directly to ice, or vice versa.

9
More on H20 phase changes

• Latent heat of vaporization the energy that is
  absorbed when water undergoes a phase change from
  a solid to a liquid or a liquid to a gas
  (boiling)
• Latent heat of condensation the energy that is
  released when water undergoes a phase change from
  a gas to a liquid or a liquid to a solid
  (freezing)
• Importance of Latent Heat in the Atmosphere -
  absorption and release of energy during
  evaporation and condensation have several effects
• Water can store energy when it evaporates
• Water can release heat back to the atmosphere
  when it condenses.

10

• Phase Changes gt exchange of Latent Heat

• Fig. 6-6

11

• Phase Changes of Water
• Animation (Phase Changes of Water)

• Fig. 6-5

12
Water Vapor and the Hydrologic Cycle

• Fig. 6-7

Hydrologic cycle the ceaseless interchange of
moisture in terms of its geographical location
and its physical state.
13
Simplified Hydrologic Cycle
Water evaporates, becomes water vapor goes into
atmosphere vapor condenses, becomes liquid or
solid state returns to Earth.
14
Water vapor the gaseous state of water
atmospheric moisture.

• Evaporation process by which liquid water is
  converted to gaseous water vapor
• Rates (Controls)
• Temperature of air
• Temperature of water
• Humidity
• Wind
• Evapotranspiration the process of water vapor
  entering the air from land sources
• Moisture sources
• Plants
• Soil
• Potential Evapotranspiration (PE)

• Fig. 6-8

15
Measures of Humidity

• Humidity the amount of water vapor in the air
• Absolute Humidity a direct measure of the water
  vapor content of air (weight of water vapor in a
  given volume of air grams of water per cubic
  meter of air)
• Specific Humidity a direct measure of
  water-vapor content expressed as the mass of
  water vapor in a given mass of air (grams of
  vapor/kilograms of air)

Absolute Humidity Graph

• Fig. 6-9

Red line is the maximum absolute humidity
16

• Vapor Pressure the pressure exerted by water
  vapor in the air

• At any given temperature, there is a maximum
  vapor pressure that water vapor molecules can
  exert
• Saturated airthe point at which some water vapor
  molecules must become liquid because maximum
  vapor pressure is exceeded

• The warmer the air, the more water vapor it can
  hold before becoming saturated

Specific Humidity Graph
Red line is the maximum specific humidity

• Fig. 6-10

17

• Relative Humidity an expression of the amount of
  water vapor in the air in comparison with the
  total amount that could be there if the air were
  saturated a ratio that is expressed as a
  percentage
• (Actual Water Vapor in Air/Capacity x 100)

• Temperature-Relative Humidity Relationship

• Fig. 6-11

18

• Related Humidity Concepts
• Dew Point Temperature
• Temperature at saturation
• Sensible Temperature
• Temperature as it feels to a persons body
• Affected by humidity and wind

19
Condensation process by which water vapor is
converted to liquid water opposite of
evaporation.

• Phase change of gas as to liquid
• Water vapor to water droplets
• Requirements
• Decrease in temperature (usually)
• A surface
• Condensation nuclei
• Grass
• Cup of water

• Fig. 6-12

20
Adiabatic Processes

• Animation (Adiabatic Processes)
• Terms
• Adiabatic
• Lapse rate
• Lifting Condensation
• Level (LCL)

• Fig. 6-14

21

• Dry Adiabatic Lapse Rate
• the rate at which a parcel of unsaturated air
  cools as it rises this rate is relatively steady
  
• 10ºC (5.5ºF) 1,000 m-1
• Saturated Adiabatic Lapse Rate
• the rate at which a parcel of unsaturated air
  cools as it rises this rate is relatively steady
  
• 6ºC (3.3ºF) 1,000 m-1

• Fig. 6-14

22

• Comparisons of Lapse Rates

Notice the mid-high level clouds above the
lifting condensation level. Clouds cover 50 of
the Earth at any given time.

• Fig. 6-15

23
Rainshadow

• Fig. 6-16 Temperature changes in air as it
  crosses over a mountain

24
Clouds

• Classification
• Cloud form
• Cirriform clouds
• Latin cirrus, a lock of hair
• Stratiform clouds
• Latin stratus, spread out
• Cumuliform clouds
• Latin cumulus, mass or pile

• Table 6-1

25
Cumuliform

• Fig. 6-13

26

• Subtypes of Cloud Forms
• High clouds
• found above 6 kilometers (i.e., cirrus clouds)
• Middle clouds
• between about 2 and 6 kilometers (i.e.,
  altocumulus and alto stratus)
• Low clouds
• below 2 kilometers (i.e., stratocumulus and
  nimbostratus)
• Clouds of vertical development
• clouds with vertical development (i.e.,
  cumulonimbus clouds)

• Fig. 6-18

27
Fog a cloud whose base is at or very near ground
level

• Types
• Radiation
• forms through loss of ground heat
• Advection
• forms when warm moist air moves over a cold
  surface
• Upslope/Orographic
• caused by adiabatic cooling when humid air climbs
  a topographic slope
• Evaporation
• when water vapor is added to cold air that is
  already near saturation

• Fig. 6-20

28

• Distribution of fog
• United States and southern Canada

• Fig. 6-21

29

• Dew the condensation of beads of water on
  relatively cold surfaces if temperature is below
  freezing, ice crystals forms
• Dew droplets
• White frost

• Fig. 6-22

30
The Buoyancy of Air
the tendency of an object to rise in a fluid

• Atmospheric Stability and Instability
• Stable airresists vertical movement
  non-buoyant, so will not move unless force is
  applied
• Unstable airbuoyant, will rise without external
  force or will continue to rise after force is
  removed
• Conditional instabilityintermediate condition
  between absolute stability and absolute
  instability.

• Fig. 6-23

31

• Determining Atmospheric Stability
• Stable Atmosphere
• At all elevations, rising air is cooler than
  surrounding air
• Air rises only if it is forced to do so.

• Fig. 6-25a

32

• Determining Atmospheric Stability
• Unstable Atmosphere
• At all elevations, rising air is warmer than
  surrounding air
• Air is unstable and rises because of its buoyancy.

• Fig. 6-25b

33

• Determining Atmospheric Stability
• Conditionally Unstable Atmosphere
• Rising air is cooler than surrounding air up to
  4,000 meters
• Condensation at 4,000 meters, releases heat, air
  becomes warmer than the surrounding air and is
  now unstable.

• Fig. 6-25c

34

• Determining Atmospheric Stability (continued)
• Unstable air is associated with distinct
  updrafts, which are likely to produce vertical
  clouds.
• Cumulous clouds suggest instability.
• Towering cumulonimbus clouds suggest pronounced
  instability.
• Horizontally developed clouds, most notably
  stratiform, characterize stable air forced to
  rise.
• Cloudless sky indicative of stable, immobile air.

• Fig. 6-26

35
Precipitation

• The Processes that Produce Precipitation
• Collision and Coalescence
• Warm clouds
• Tropics and mid-latitudes
• Droplets to raindrops

• Fig. 6-27

36

• Bergeron process
• Cold clouds w/ Ice Crystal Formation
• Middle and polar latitudes
• Snowflakes or raindrops

• Fig. 6-28

37

• Forms of Precipitation
• Rain the most common and widespread form of
  precipitation, consisting of drops of liquid
  water
• Fig. 6-29
• Snow solid precipitation in the form of ice
  crystals, small pellets, or flakes, which is
  formed by the direct conversion of water vapor to
  ice.
• Sleet small raindrops that freeze during decent,
  reaching ground as small pellets of ice
• Glaze rain that turns to ice the instant it
  collides with a solid object
• Hail rounded or irregular pellets or lumps of
  ice produced in cumulonimbus clouds as a result
  of active turbulence and vertical air currents
• Fig. 6-30

38

• Forms of Precipitation through Atmospheric
  Lifting

• Convective occurs when unequal heating of
  different air surface areas warms one parcel of
  air and not the air around it spontaneous (a)
• Orographic caused when topographic barriers
  force air to ascend upslope external force (b)

• Frontal occurs when air is cooled to the dew
  point after unlike air masses meet, creating a
  zone of discontinuity (front) that forces the
  warmer air to rise over the cooler air external
  force (c)
• Convergent showery precipitation caused by
  convergent lifting, the least common form, which
  occurs when air parcels converge and the crowding
  forces uplift, enhancing instability external
  force (d)

39
Global Distribution of Precipitation

• Average Annual Precipitation Animation
• (Seasonal Pressure and Precipitation Patterns)
• Very High Levels
• Tropical regions
• ITCZ
• Trade winds
• Monsoon areas
• Upper Middle Latitudes
• West coasts
• Orographic lifting

• Very Low Levels
• Subtropical latitudes
• Subtropical High Pressure dominates
• Middle Latitudes
• Rain shadow areas
• High Latitudes
• Low evaporation rates
• Cold, dry air

40
Distribution of Precipitation

• Fig. 6-34

Nature of an air mass and the degree to which
that air is uplifted determine the amount of
precipitation in an area.
41

• Seasonal Precipitation Patterns

• Shifting of ITC Zone
• Worldwide Summer Maximum
• Monsoon Areas

- Fig. 6-35 top
42

• Precipitation Variability

• U.S. Average January and July precipitation.
• Fig. 3-16 top and bottom, dissolve overlay,
  toggle

43

• Precipitation Variability (continued)

• Percent departure from average precipitation in a
  given year

44
Acid Rain

• Sulfuric and Nitric Acids in Rain
• Acidity
• pH less than 5-6
• Fig. 6-38

Cause human-industry (sulfur dioxide from smoke
stacks) Effect dying fish and forestshumans?
45

• Acid Rain in North America

46
Homework

• Read Ch. 6
• Recreate the Water Cycle
• Illustration (color preferred)
• With all components (names and arrows)
• Add text for explanation as necessary
• Must be legible!
• Due next week (or) before the midterm