Weather Station

The weather in the tropics can be unpredictable. And there's no radio or TV station to turn on and get a reliable forecast. That's why you'll need a weather station to figure out what changes lie ahead. You'll want advance warning if that big storm is on the way. And you'll want to know which direction it's coming from.

The Challenges!

Find the Dew Point

The island climate is completely different from the one you're used to. How do you avoid getting caught in a torrential storm or a thick fog? The dew point is the temperature at which moisture in the air begins to form dew. It is a way of gauging the air's humidity. Here's a way to calculate it.

You'll need:

• tin can
• thermometer
• tablespoon
• ice cubes
• paper towel
• bowl
• water

What you do:
Crush the ice cubes in the paper towel using the back of the tablespoon. Fill the bowl halfway with crushed ice. Make sure the outside of the tin can is completely dry. Fill the can with cold water. Place the thermometer in the can. Add one tablespoon of crushed ice and stir. Continue adding ice until a layer of dew is visible on the outside of the can. Immediately read the thermometer to find the dew point temperature. If it's high, beware! The humidity is high also.

What's going on?
All air contains water vapor. As air cools (when it comes in contact with the cold can), the water vapor begins to condense. This is why glasses holding cold drinks "sweat" in the summertime. The dew point is the temperature at which moisture in the air begins to form dew. The higher the dew point temperature, the higher the moisture content of the air at a given temperature.

Activity adapted from Robert Wood. Science for Kids: 39 Easy Meteorology Experiments. TAB Books, 1991.

Make a Barometer

A barometer shows changes in air pressure. High pressure indicates good weather, low pressure indicates possible storms. By consulting your barometer every day, you'll be able to make predictions about weather changes. (This can be a multi-day activity to compare the daily differences in air pressure.)

You'll need:

• tall glass or jar
• bowl
• 4 paper clips
• pen
• water

What you do:
Slide the paper clips onto the rim of the glass and space them equally around the rim. Fill the glass about two-thirds full with water. Place the bowl upside down over the glass. Carefully turn the bowl and the glass over so that the glass sits upside down in the bowl. Some of the water will run out of the glass but most will stay inside it. With a pen mark the level of the water in the glass at the beginning of the activity. Take your barometer outside into the open air. Look for changes in the water level in the glass over time. (This may take several hours or even longer than a day.)

What's going on?
When the atmospheric pressure of the air rises, the water in the bowl will be forced downwards by the weight of the air on the water. This, in turn, will cause the water in the glass to rise. A barometer measures the weight of the amount of air between the surface of the earth (the water in the bowl) and the top of the atmosphere.

Activity adapted from Robert Wood. Science for Kids: 39 Easy Meteorology Experiments. TAB Books, 1991.

Make a Compass

Make a compass to determine the different directions: North, South, East, and West.

You'll need:

• needle
• magnet
• plastic container
• a cork (1/4" to 1/2 " thick)
• pen
• water

What you do:
Fill the plastic container with water. Stroke one end of the magnet along the needle in one direction at least 50 times to magnetize the needle. Lay the needle on the cork, with one end of the needle in the center. Tape the needle down. Float the cork in the container of water. The needle will bob around until it points North, towards the Earth's magnetic north. When the needle settles in position, mark North on the side of the container. Now you can determine the other directions and label them East on the right, South on the bottom and West on the left.

What's going on?
The Earth's core is thought to consist largely of molten iron, which crystallizes into a solid. Convection caused by heat radiating from the core, along with the rotation of the Earth, causes the liquid iron to move in a rotational pattern. It is these rotational forces in the liquid iron layer that lead to weak magnetic forces around the axis of spin. The magnetized needle in a compass can detect very slight magnetic fields. No matter where you stand on Earth, you can hold a compass in your hand and it will point toward the North. This is amazingly helpful because you can tell which way to go no matter what the weather or time of day.

Build a Wind Vane

A change in wind direction often indicates an imminent change in the weather. Be prepared for sudden change by making this wind vane. (You can also use the compass you made in the previous activity to identify the direction of the wind.)

You'll need:

• a long tack
• scissors
• modeling clay
• a plastic pot or container, e.g., from take-out food
• ruler
• glue stick
• thin, colored card
• drinking straw
• 2 pencils with eraser
• compass

What you do:
Turn the plastic container upside down. Make a hole in the center by inserting the pencil, sharp end first. Make sure that it is firmly in place. With another pencil and a ruler, draw two large triangles and four small ones on the colored card. Then cut out the shapes. Glue the small triangles to the base of the plastic container at equal distances and on opposite sides from each other as on a compass. One point of each small triangle should overlap the edge of the pot, with the pencil in the middle. Cut short slits in each end of the straw and insert one large triangle in each end to make an arrow-shaped "vane." Push the tack through the center of the straw and into the eraser on the pencil sticking out of the pot. Secure the other end of the pot to a surface with a ring of modeling clay. Take the vane outside or to a simulated windy weather area and watch it swing in the wind. Finally, use your compass to determine East, West, North and South, and then label the small triangles accordingly. Now you can tell which direction the wind vane is pointing.

What's going on?
The direction in which the vane points indicates the direction from which the wind is blowing. For instance, in a westerly wind, the vane points "West."

Activity adapted from Neil Ardley. 101 Great Science Experiments. Dorling Kindersley, 1993, pp. 14-15.