Download Water in the Atmosphere

Moisture,
Clouds and
Precipitation
Chapter 18
H2O exists in
atmosphere in all
three states of
matter…
Solid:
snow
hail
ice
Liquid:
rain and cloud
droplets
Gas:
invisible H2O
vapor
When it comes to understanding
atmospheric processes, water
vapor is the most important
gas in the atmosphere.
H2O may change from one
state to another:
What is latent heat?
The process of changing state
requires that energy is transferred
in the form of heat
Energy is absorbed or released during
state change
What is Melting?
• from solid ice to liquid H2O
What is
Freezing?
• liquid H2O to solid ice
What is Evaporation?
• from liquid H2O to H2O vapor
What is Condensation? from H2O
vapor to liquid H2O
What is Sublimation? change
from solid to H2O vapor
Example: Dry ice
What is Deposition? change
directly from H2O vapor to a
solid
Warmer the air, the more H2O
vapor it can hold
• What is
Humidity?
water vapor in
the air
• What is Relative
humidity?
the % of moisture
the air can hold
relative to the
amount it can hold
at a certain
temperature
Relative humidity=specific humidity X 100
capacity (saturated)
Psychrometer: instruments used
to measure relative humidity
• Works on principle
that evaporation
causes cooling
• 2 thermometers…wetbulb and dry-bulb
• Readings show how
dry the air is
What is Dew point? the
temperature at which
water vapor condenses
• Dew, clouds, and fog forms
• If dew point is below
freezing, frost will form
What are Clouds?
simply high fog, mist,
or haze
• Form when air above surface
cools below dew point
• Clouds are classified on the
basis of their form and height
What determines cloud shapes?
•Shape depends on air movement
that forms it:
-horizontal air movement = layers
-vertical air movement = piles
• Temperature above freezing – clouds
drop water
• Temperature below freezing – clouds
drop snow crystals
What are the
three main cloud
types?
CIRRUS:
- thin, feathery, made of ice crystals
- form at high altitudes
- seen when weather is fair, but can
mean rain or snow
- “a curl of hair”
STRATUS
•
•
•
•
Low sheets or layers; gray and smooth
Block out the sun
Associated with rain and drizzle
“a layer”
CUMULUS
• Piled in thick, puffy masses
• Usually mean fair weather
• “a pile”
Other cloud
types:
Cirrostratus
Stratocumulus
Cirrocumulus
Altocumulus
Nimbostratus
Cumulonimbus:
large cloud that produce
LIGHTNING, THUNDER,
HEAVY SHOWERS =
Thunderstorms
What is
Precipitation?
• Water that falls from the atmosphere to
the earth
• Occurs when cloud droplets grow into
drops heavy enough to fall to Earth
• Type of precipitation that reaches
Earth’s surface depends on the
_______________in the lower few
kilometers in the atmosphere
Condensation nuclei: suspended
particles that provide the necessary
surfaces for cloud forming
condensation.
What are the FORMS OF
PRECIPITATION?
• Drizzle: fine drops….less than 0.5mm
diameter
• Rain drops: larger… 0.5mm to 5mm
diameter
• Snow: falls in clumps of six-sided crystals
• Sleet: pellets of ice that fall to the ground
when raindrops fall through freezing air
for precipitation to form, cloud
droplets must grow in volume by
roughly one million times!
• Hail:
forms in cumulonimbus clouds-
irregular balls or lumps made of layers of ice
What is a Rain
gauge?
instrument used
to measure the
amount of
rainfall
What is Acid precipitation? acid
drops that fall to the ground
- contain nitrate and sulfate
particles that come from burning
fuels, volcanoes and cars
http://www.epa.gov/acidrain/site_students/acid_anim.html