Download Fog and Precipitation

Fog and Precipitation
• List in three steps how to form a cloud
• List in three steps how to form a cloud
1. Warm air rises
2. Cooling down
3. Stick to condensation nuclei
Fog
• A cloud with its base very close to or at the
ground.
Fog
• Generally the same as clouds except for the
method and place of formation.
Fog
• Results from hot air moving over a cold
surface.
Fog
• Can be caused by cooling or evaporation.
How Precipitation Forms
• What do you think?
How Precipitation Forms
• Forms from tiny water droplets that are less
than 20 micrometers.
• For precipitation to form these cloud droplets
must grow in volume by roughly one million
times.
Cold Cloud Precipitation
• Bergeron Process – relies on two processes.
1. Supercooling  water droplet below its
freezing point. Not frozen yet.
2. Supersaturation  water vapor content is
over 100%
Warm Cloud Precipitation
• Collision-Coalescence Process happens when
– One drop of water moves round the cloud
colliding and coalescing (joining) with other drops.
– Will then fall as rain.
Forms of Precipitation
• The type of precipitation depends on the
temperature of the lowest few kilometers of
the atmosphere.
Forms of Precipitation
• Rain means drops of water that fall from a
cloud.
• This happens when the temperature is above
4°C
Forms of Precipitation
• Snow happens when the temperature is very
low.
Forms of Precipitation
• Sleet happens when a layer of air with a
temperature above freezing must overlie a
subfreezing layer near the ground.
Forms of Precipitation
• Freezing rain – glaze – forms when raindrops
become supercooled and turn to ice when
they hit something.
Forms of Precipitation
• Hail is produced in cumulonimbus clouds.
• Begin as small ice pellets and collect other
supercooled water droplets as they fall.
1. How are clouds classified?
2. Compare and contrast clouds and fogs.
3. What must happen in order for precipitation to
form?
4. Describe how the temperature profile of air near
Earth’s surface controls the type of precipitation
that falls to ground.
5. What type of precipitation would fall to Earth’s
surface if a thick layer of air near the ground was
-8°C
6. Write a paragraph comparing the Bergeron and
Collision-Coalescence processes. Relate each to the
types of precipitation that can result.