Key for cloud webquest
Analysis Questions:
1.1 What are the three necessary ingredients for cloud/fog formation?
A, water vapor
B. a change in temperature and/or pressure
C. Condensation nuclei: particles for water to form on
2.1 Define the following ways that air forms clouds:
Adiabatic cooling: the cooling caused by the separation of molecules as warm air rises and
spreads due to decreased pressure with altitude
Adiabatic lapse rate: the rate at which temperature decreases as an air mass rises (average is
about 6.5°C/km)
Advective cooling: As warm air mass moves over a cold surface heat moves from air to surface
and air cools.
Lifting/The Foehn Effect: As air moves against topographic elements (like mountains or even
buildings) the air mass is forced upward. As it moves upward it is cooled
Mixing: As warm and cold air masses come together, energy is transferred. Cold air masses also
move warm air masses up in altitude where they cool by adiabatic cooling.
3.1 What are the four processes of cooling that can lead to cloud formation? Draw a
diagram of each.
See above: many answers accepted.
4.1 Why does air expand when it rises?
Because air pressure decreases with altitude
5.1 look at the three diagrams of stable and unstable air masses. Describe the differences
in temperature, relative humidity and lapse rate between stable, unstable and conditionally
unstable air masses.
Temperature: Unstable the difference in temperature is from 40°C to -8°C while in stable it is
much less 20°C to – 5°C. Conditional instability is like unstable but you do not reach 0° degrees
until a much higher altitude.
Environmental Lapse Rate, how fast the air cools is much higher than the adiabatic lapse rate for
unstable air than it is for stable air. In unstable air masses the environment is colder than the
clouds. In stable air the environment is warmer than the clouds.
Relative humidity: usually higher in unstable than stable
6.1 How does the adiabatic lapse rate change for air that has a high relative humidity
versus air that has a low relative humidity?
Wet air has a lower adiabatic lapse rate (6°C/km) vs. dry adiabatic lapse rate (10°C/km)
7.1 What is the difference between clouds and fog?
Fog forms at the surface of the earth, clouds form at altitude
8.1 Describe four ways fog can form.
Radiation fog: occurs under clear, calm skies when infrared radiation (heat) escapes
Key for cloud webquest
to upper atmosphere and outer space and the air is cooled to its dew point. Sometimes
called valley fog or ground fog and is the most common fog over land in
the world.
Advection fog: occurs when warm, humid air is cooled to its dew point by coming
into contact with a cooler surface below. Snow, ice, and cold water are common
surfaces that cause advection fog.
Steam Fog - occurs when cooler air rests above warmer water and vapor that
evaporates into the air cools to its dew point. Sometimes called Arctic sea smoke.
Frontal Fog - also knows as precipitation fog and occurs when rain drops fall into
unsaturated, cooler air below. As the drops evaporate, water vapor is introduced
into the cooler air. Very quickly, the vapor condenses into a small fog droplet.
9.1 How might pollution affect the formation of clouds and fog.
More particles = more condensation nuclei = more clouds/fog
1.2. What 2 features of clouds are used to categorize them?
Altitude and shape
2.2. List the words that describe the altitude where you find the different cloud types
cirr - high, ice, all white, very thin
alto - middle, ice and/or liquid, white and grey, thin
cumu - puffy appearance, all vertically-developed clouds begin with "cumu"
nimb - cloud must be precipitating
strat - cloud is spread out, most likely covers the sky
3.2. Describe the following cloud types
a. Cirrus: whispy, feathery and composed of ice crystals. The first sign of approaching warm front
or upper level jet-stream
b. cirrocumulus: are layered clouds permeated with small cumuliform lumpiness. They also may line up
in streets or rows of clouds across the sky denoting localized areas of ascent (cloud axes) and descent
(cloud-free channels).
c. altocumulus: exhibit "cumulo" type characteristics (see below) in mid levels, i.e., heap-
like clouds with convective elements. Like cirrocumulus, altocumulus may align in rows
or streets of clouds, with cloud axes indicating localized areas of ascending, moist air,
and clear zones between rows suggesting locally descending, drier air.
d. altostratus: are "strato" type clouds (see below) that possess a flat and uniform type
texture in the mid levels. They frequently indicate the approach of a warm front and
may thicken and lower into stratus, then nimbostratus resulting in rain or snow.
e. stratocumulus: clouds are hybrids of layered stratus and cellular cumulus, i.e.,
Key for cloud webquest
individual cloud elements, characteristic of cumulo type clouds, clumped together in a
continuous distribution, characteristic of strato type clouds. Stratocumulus also can be
thought of as a layer of cloud clumps with thick and thin areas. These clouds appear
frequently in the atmosphere, either ahead of or behind a frontal system.
f. cumulus: The outline of L2 clouds are usually clear cut, with horizontal bases and cauliflower shaped
tops. Sunlit parts are mostly brilliant white, while bases are relatively dark. The clouds are sometimes
arranged in lines, called cloud streets, nearly parallel to the wind direction. They may also form with tall
towers that may be tilted by the wind. Showers can occur with these clouds but will not contain lightning and
thunde
g. cumulonimbus: If enough atmospheric instability, moisture, and lift are present,
then
strong updrafts can develop in the cumulus cloud leading to a mature,
deep cumulonimbus cloud, i.e., a thunderstorm producing heavy rain.
4.2 Cirrus: very high, whispy clouds
5.2 Stratus: lower clouds, like a blanket across the sky.
5.3 Cirrocumulus: Mackeral sky, very high but individual little cells schooled together
5.4 Cumulus: puffy clouds takes up multiple altititudes.
1.3) How do clouds keep the earth cool?
Clouds cool the Earth by reflecting incoming sunlight. Thus the net effect of clouds on
the climate is to cool the surface by about 5°C, at least under the current global
distribution of clouds.
2.3) How do clouds make the earth warmer?
Clouds warm the Earth by absorbing infrared radiation emitted from the surface and
reradiating it back down.
3.3) Why does a cloudless desert sky at night mean that the temperature will get much colder?
No clouds to re-radiated surface infrared
4.3) Which kinds of clouds make the earth warmer: high clouds or low clouds?
high clouds have a net warming effect, because they block little incoming solar radiation
but, being so cold, they return little outgoing infrared radiation back to the Earth surface.
Low clouds have a net cooling effect, because they have a high albedo, and, being nearly
as warm as the surface, they emit nearly as much infrared radiation to space as would the
surface under clear skies.
1.4 Write down the four steps described in "How to forecast the weather using clouds" give you to
predict the weather by watching clouds. You may need to scroll down a lot to get to that section.
1. Take several days of observations for 2 areas
2. Research what weather is expected in your area
3. compare the climate in the two areas
4. If things start to get unusual, that means there might be a drastic change in the
weather, or just a quick shift.
2.4 What weather might you expect if you see the following clouds
a. Stratus: drizzle or fine snow
Key for cloud webquest
b. Nimbostratus: precipitation as rain and snow, continuous
c. Altocumulus: if seen on warm, sticky morning expect thunderstorms in afternoon
d. Altostratus: usually occur a few hours before the arrival of a warm front that can bring
precipitation
e. Cirrus: if gradually increasing, usually means the arrival of a warm front that may bring
precipitation
f. Cirrostratus: usually come 12-24 hours before rain or snow
g. Cirrocumulus: usually show fair but cold weather except in tropics where they indicate
oncoming hurricane
h. Cumulus: usually show “fair” and dry conditions. If they do bring precipitation it is light and
quick
i. Cumulonimbus:: Thunder clouds, anvil headed clouds. Show extreme weather heavy rain, hail,
tornado, hurricane. Anvil points in the direction storm is moving.