Activities
*Cloud in a Jar with Calvin*
Supplies:
Glass jar with lid (or
use a small bowl/plate to act as a lid)
Hot water
Ice
Dark colored paper
Aerosol (i.e. hairspray or air refreshener) or Matches
Flashlight (optional)
Directions:
This activity requires adult
supervision due to the use of hot water, glass, and the aerosol or matches.
First, make sure the glass
jar is clean. Fill the bottom of the glass jar with hot water (approx. 1"
deep). You may want to swirl the hot water on the sides of the jar to warm
up the glass, otherwise, condensation will immediately occur. Take the lid
of the glass jar and turn it upside down so that it acts as a small bowl.
Put ice in the lid and place the lid on top of the jar. Notice that while
you may have some condensation on the glass, there is no cloud floating inside
the jar. Next, take a can of air refreshener or hair spray, lift the lid of
ice, spritz a small amount of aerosol into the jar and quickly place the lid
of ice on top of the jar. (Instead of an aerosol, an adult can light a match,
blow it out, then throw the smoking match inside the jar and replace the lid
of ice.) Now hold up the dark colored paper to the glass and look for wisps
of cloud to start swirling inside. You may also want to shine a flashlight
inside the jar to see the cloud better. Lift the lid and let the cloud out
so that you can touch it.
Click
on Calvin to see photos of this activity.
Discussion:
Congratulations, you just
made a cloud! But how did it work and how can this activity help us understand
weather in Hawaii?
Just like a baker uses a
recipe to bake a cake, the atmosphere must have three ingredients to make
a cloud: 1) moisture, 2) lifting/cooling, 3) Cloud Condensation Nuclei (CCN).
The moisture was provided by the hot water in the bottom of the jar. Some
of that hot water evaporated into water vapor so that the air inside the jar
would be moist and warm. As the warm, moist air rises in the jar, it gets
cooled by the ice on top. When water vapor cools, it wants to turn back into
liquid, but it needs to condense onto a surface. The aerosol (or smoke from
the match) provides a surface for the water vapor to condense into tiny cloud
droplets. It's called Cloud Condensation Nuclei because it's a very small
particle that can float in the air to help water vapor condense into clouds.
The cloud swirls inside the jar due to the circulation of warm air rising
and cold air sinking.
The islands of Hawaii act
just like the jar. Some of the water in the ocean evaporates into the air
providing moisture. When the islands heat up during the day, it heats that
moist air so that it will rise. (This process is called convection.) The higher
up you go in the sky, the colder the air gets. Think about climbing up Mauna
Kea, it's much colder up on top of the volcano then down at the beach. The
ice in the experiment represents the atmosphere cooling as the air rises.
When that water vapor is cold enough to condense it has many choices of CCN.
The aerosol (or smoke) represents small particles floating in the air. In
Hawaii, the most common CCN are sea salt aerosols, but CCN can also be dust,
smoke, air pollution or volcanic vog.
Have you seen the clouds
that often form on the windward coasts of the islands? The same concept can
be applied, except the air doesn't rise from the land heating up during the
day. Instead, the air rises with the wind. The Tradewinds carry moist air
from over the ocean. When the Tradewinds run into the mountains, it carries
that moist air up the mountain where the air is colder and the water vapor
condenses onto CCN and becomes a cloud.
*Colored Convection with Wendy Wind*
Supplies:
Glass pie pan
Food Coloring
Eye Dropper
4-5 Styrofoam Cups
Ice
Hot water
Directions:
Take 3 styrofoam cups and
place them upside down in a triangular shape. Place the pie pan on top. Fill
pie pan 3/4 full with water at room temperature. Take another cup, fill it
with hot water then carefully slide it under the center of the pie pan. Try
not to touch the pie pan so that the water inside remains still. Put a few
drops of food coloring inside the eyedropper. Next, let the eyedropper touch
the bottom of the pie pan right above the hot water. Squeeze out 1 or 2 drops
of color, then carefully remove the eyedropper. Watch the movement of the
food color inside the pan. Look at it from above and also from the sides.
Draw what you see.
Try this experiment again,
except place a cup of hot water near the side of the pan and a cup of ice
under the center of the pan. Sqeeze 1-2 drops of color above the hot water.
How does the food color move this time?
Click
on Wendy to see photos of this activity.
Discussion:
Congratulations! You just
created a convection cell! Convection is the movement of mass within a fluid.
That fluid could be water (like the ocean), but air is also considered a fluid.
In meteorology, convection means the upward movement of air. A convection
cell is the circulation of air that includes both upward and downward motion.
Did you notice how the drops of color move in the pie pan? Look from the side
of the pan. You should see the color rising if it's near the cup with hot
water and sink when it's near the cup with ice.
This activity is a great
example of sea breezes in Hawaii during the day. If the trade winds are very
light or not even blowing, then the islands will develop sea or land breezes
(depending on day or night).
Sea Breeze
If the sun is out, it heats
up the land so that it is much warmer than the ocean. This causes the air
above the land to heat up while the air over the ocean is cooler. Hot air
will rise and cool air will sink. Together, this rising and sinking motion
creates a convection cell just like in the activity. The cup of hot water
represents the land heated by the sun. The ocean is cooler than the land and
is represented by the cup of ice. The water inside the pie pan represents
the air above the ocean and land. The food coloring allowed us to see the
movement of the water.
Look at the diagram below:
As the warm air rises over
land, it must be replaced by the cooler air over the ocean. We call this a
sea breeze because it's a breeze that comes from the sea. Meteorologists always
name winds based on where they come from. (If you were born and raised in
Hawaii, then went to visit the Mainland, you would tell people that you were
from Hawaii.)
Land Breeze
At night time, the convection
cell is reversed and we call it a land breeze because the wind near the surface
now blows from the land out to sea. This happens because the land cools down
at night and will get colder than the ocean. The air above the ocean is now
warmer compared to the cooler air over the land at night. (Have you ever noticed
how the ocean feels warmer in the evening? It's not because the ocean heats
up at night, it's because the air at night got colder.) This is seen in the
diagram below:
It is important to understand
that the ocean's temperature doesn't change much in a given location. It's
quick and easy to heat up a cup of water...but it would take a very long time
to heat up the entire ocean! When we talk about land and sea breezes, these
winds occur due to the land being colder or warmer than the ocean. That causes
the air above land to be a different temperature than the air above the ocean.
Also, keep in mind that land and sea breezes have a difficult time developing
if the trade winds are blowing strong because this disrupts the convection
cell.
Activity Photos.....
Cloud
in a Jar
Photo 1: Before Aerosol (match)...........................Photo
2: After Aerosol (match).............................Photo 3: Lid removed
to release cloud
Convection
Cell
Photo 1: Setup...............................................................................Photo
2: Drop of food color over hot water
Photo 3: Food color begins to rise and move towards cold water.....Photo
4: Food color continues to spread away from heat source
Photo 5: Food Color rises over hot water.......................................Photo
6: Food Color begins to sink over cold water
weather.gov 
