1. CLOUDS AND PERCIPITATION
BY SARAH MURPHY

2. Adiabatic Temperature Changes and
Expansion and Cooling
• Temperature changes even though heat isn't added
or subtracted.
• When air expands, it cools. When air compresses, it
warms up.
• Dry adiabatic rate:
Rate of adiabatic warming or
cooling of unsaturated (dry) air.
• Wet adiabatic rate:
Rate of adiabatic temperature
changes in saturated air.
http://www.kidsgeo.com/geography-
for-kids/0070-adiabatic-temperature-
changes.php

3. Orographic Lifting
• Places that are elevated act as barriers, or
walls, to air flow, making air rise.
• Air cools, which may result in clouds
appearing, and even precipitation.
http://www.nc-
climate.ncsu.edu/edu/k12/.Lifting
Mechanisms

4. Frontal Wedging
• When masses of warm and cold air collide, it
creates a front.
http://santas
usana.org/pa
kelly/ES9CP/E
S9%20clouds
.htm

5. Convergence
• The collision of contrasting air masses make
air rise. When air in the lower atmosphere
flow together, air rises.
• Air can’t go down, so it goes up, which leads
to cooling, and sometimes makes clouds form.
http://www.thekeytoisla
m.com/en/scientific-
explanations/clouds-
and-rains.shtml

6. Localized Convective Lifting
• Air above a paved parking lot will warm up more
than a wooded area. Air above the parking lot is
less dense than the surrounding air.
• During the summer, unequal heating of Earth’s
surface causes some spots of air to be warmed up
more than the rest of the surrounding air.
http://rst.gsfc.nasa.gov/Sect14/Sect
14_1c.html

7. Stability (Density Differences and
Stability and Daily Weather)
• Temperatures that are warmer than the
surrounding air rise until it reaches an altitude
where the temperature is equal.
• Stable air stays in same place, unstable air rises.
• Clouds won’t form when there is stable conditions in
the atmosphere.
http://stab
ilitycloud.c
om/

8. Condensation
• The air must be saturated in order for water
vapor in the air to form dew, fog or clouds.
• Saturation occurs when air is cooled to its dew
point, but saturation doesn’t really occur
when water vapor is in the air.
http://decorating.visitac
asas.com/how-to-
combat-condensation/

9. Types of Clouds
• Cumulus clouds:
Round, individual clouds.
Flat based, rising into dome or tower-like shapes.
• Cirrus clouds:
White and thin, high in the sky.
• Stratus clouds:
Layers that cover up most of the sky.
No distinct individuality. http://www.xconomy.com/bo
ston/2011/03/22/clouds-
clean-air-cancer-and-cardio-
some-massachusetts-
companies-on-the-rise/

10. High Clouds
• Cirrus, cirrostratus, and cirrocumulus.
• Thin and white.
• Made of ice crystals, due to low temperature,
and high altitude.
http://scienceray.com/earth-
sciences/meteorology/clouds-
types-and-how-they-are-formed/

11. Middle Clouds
• Ranges from 2000 – 6000 meters high.
• Altocumulus clouds.
• Larger and denser than cirrocumulus clouds.
http://scienceray.com/earth-
sciences/meteorology/clouds-
types-and-how-they-are-formed/

12. Low Clouds
• Stratus, stratocumulus, and nimbostratus
clouds.
• Fog-like, covers most of the sky.
• Nimbostratus clouds produce precipitation.
http://scienceray.com/earth-
sciences/meteorology/clouds-
types-and-how-they-are-formed/

13. Clouds of Vertical Development
• Clouds that do not fall in the 3 height
categories are associated with unstable air.
• The end result of clouds with great vertical
forms are rain showers or thunderstorm.
http://www.uwgb.edu/du
tchs/EarthSC102Notes/10
2Clouds.htm

14. Fog by Cooling and by Evaporation
• Fog is clouds that are very low to the ground.
• Fog that is caused by cooling usually forms where
moist and warm air is carried to the shorelines by
prevailing winds.
• Fog that is caused by evaporation
forms when cool air moves over
warm air, which rises due to the
different kinds of air meeting.
http://www.brainhar
monycenter.com/brai
n-fog.html

15. Cold Cloud Precipitation
(Bergeron Process)
• The Bergeron Process relies on supercooling
and supersaturation to freeze the water in
the air.
• Pure water in the air doesn’t freeze until it
reaches -40 degrees Celsius, instead of 0
degrees Celsius.
http://alibanfm.wordpress.com/

16. Warm Cloud Precipitation
(Collision-Coalescence Process)
• Water absorbing particles can remove water
vapor from the air, which forms droplets that
are big.
• The big drops collide with smaller droplets in
the air.
http://www.cbs
6albany.com/sec
tions/weather/r
esearch/topics/t
opicfive/

17. Rain and Snow
• The term rain means drops of water that fall from a
cloud and have a diameter of about 0.5 mm.
Anything smaller is called a drizzle.
• Snowflakes usually melt before they hit the ground.
• Snow is made up of 6 sided ice crystals.
http://warebuzz.com/dx-winter-snow-
screensaver.html

18. Sleet, Glaze and Hail
• Glaze is supercooled freezing rain.
• Hail is made in cumulonimbus clouds.
• Sleet is the fall of small particles of clear or
transparent ice.
http://cocorahs.or
g/Content.aspx?p
age=hail