We can define weather as the condition of the atmosphere at a particular time and a particular place. As this condition determines what we will wear and what we will do for activities, we should understand something about the basic weather elements and their bearing on the total weather picture.
The basic symbol on the weather map is a circle where numbers and symbols are organized around. Each element has a particular position around the circle to place their value. The center of the cycle will tell a person how much of the sky is covered with clouds. This makes clouds the logical element to investigate first.
Clouds
We are familiar with the water cycle so the student should understand that clouds form from condensation in the atmosphere. The student will first observe the cloud cover and record this observation using the appropriate method on a station model. As for the clouds themselves, we will concern ourselves with the basics and their base elevations. Cumulus clouds, puffy, will use a base height of +1 mile and the symbol . Stratus clouds, layered , will use a base height of +1 mile and the symbol —-. Cirrus clouds, wispy, will use a base height of +3 miles, but are generally higher, and the symbol . We are interested in clouds as their size, shape and location give a key to what is happening with the water vapor in the atmosphere and air movement.
A simple way to show cloud formation is to use a cloud forming apparatus. If you do not have one, your science representative can probably track one down for you to borrow to demonstrate cloud formation for your class. The device consists of a glass flask, rubber bulb and inlet tube. Compressing and releasing the rubber bulb causes condensation and cloud formation. When performing this demonstration it is best to have a little smoke or dust particles inside the chamber to serve as a nuclei for the water vapor.
Winds
Winds are defined as air in motion. On a station model, the direction the wind is blowing from is represented by a staff. Barbs are placed on this staff to show wind speed.
Winds basically blow from high pressure areas to low pressure areas. The greater the differences in pressure, the stronger the wind. There are other influences that play a part in wind direction. One is Earth rotation which causes the Coriolis effect. This causes the winds in the northern hemisphere to deflect to the right and just the opposite in the southern hemisphere. The other factor is the heating and cooling of water vs. land. The temperature of water is more stable than that of land. This causes the air to have different densities at different times of day and seasons. This difference in their densities causes air movement.
There are places on Earth that winds blow with predictable regularity. They are the trade winds. The prevailing westerlies and the polar easterlies are not as regular. Basically, the cold air over the poles moves towards the equator. At the equator, the warm air rises, moves back toward the north pole, cools and falls back to earth to start the cycle again.
During World War II, the jet were discovered by airplanes doing high altitude bombing raids. They found that between the altitudes of 6 Km and 12Km a belt of high speed winds existed that moved at speeds upward to 500 Km/hr. Further investigations of this phenomena show that the jet stream plays an important part with weather determination. Students could do a research paper on the jet stream.
At this time, the student will construct two instruments for measuring wind. A wind vane for wind duration and an anemometer for measuring wind speed.
As mentioned earlier, there are a variety of ways to make weather instruments. I will briefly tell one method for the wind vane. You will need a 3’ by 5’ file card, a test tube, 2 drinking straws, 3 paper clips, sharpened pencil and a stapler You will first staple the straws to the index card, next bend the straws around the test tube and clip them together in front using the paper clips. Finally, place the test tube over the point of the pencil and it is ready for operation.
An anemometer can be constructed using 4 paper cups, wood strips, coat wire, medicine dropper and a block of wood for the base. Place a straight piece of coat hanger wire into the wood base. Connect the wood strips together forming right angles and attach the four cups to each end of a wood strip. Color one cup different from the rest of the cups. Drill a hole in the center of the wood strips and place the medicine dropper in the hole. Place the wood strips with the cups over the wire hanger wire. The cups can now turn freely in the wind and can be used as an anemometer.
To calibrate the anemometer have the student take it home and have a parent or relative ride them in a car at speeds of 5 mph and 10 mph. Count the number of times the colored cup rotates in a minute at this speed and use this as your speed guide.
Air Pressure
Because air is matter, it has weight and takes up space. Different examples can be used to show this. We can blow up a balloon to show that it has volume. Weight can be a little more difficult to demonstrate. One way is to do the can crushing demonstration. The student should be aware that warm air and cold air have different densities making them weigh different for the same volume as discussed from earlier units.
The procedure is to place a small amount of water in a can that can be sealed. You heat the can and water. When the water starts to boil you remove the can from the heat source and seal the container. As the container cools, it begins to buckle. At this time you will ask the student why this is happening. At least one student will probably say that the pressure on the on the outside is greater than the pressure on the inside You can then ask them what causes pressure. If you want to go one step further, ask the student what they think will happen if you reheat the can. The can will take the original shape. This demonstration will also support the idea of more room for water vapor in warm air the cold air.
The rising or falling of barometric pressure is an indicator for the type of weather that is expected. When the barometric reading starts to fall, this usually indicates the air that was closer to the earth’s surface is rising. This layer of air is warmer and contains more water vapor than it can hold at high altitudes. As this air rises, the barometric reading goes down and the water vapor condenses and may form clouds or cause precipitation. This is why a falling barometer indicates cloudy or stormy weather.
Just the opposite happens with a high pressure reading. The air from above descends and causes the barometric reading to rise. The air from above generally doesn’t contain enough water vapor to cause precipitation and we can safely say we will experience good weather.
The barometric reading is located in the upper right of the station model. Standard air pressure is about 760mm
A barometer can be constructed by using a thin sheet of rubber (part of a balloon) , a jar, masking tape, quick drying cement, needle, paper soda straw and shoe box.
Place the thin sheet of rubber over the jar and secure it so that no air can enter or exit. Attach the needle to the straw and attach the straw to the rubber sheet. Draw 10 lines on an index card and number them form one to ten. Note the weather conditions and the position of the pointer on your homemade barometer. Monitor if the needle or falls and relate it to the weather conditions.
Temperature
We will refer back to our definition of temperature as the average kinetic energy of a substance that is measured in degrees. The scale that the student will use in this science unit is the Celsius scale. They should be aware that water freezes at 0 and boils at 100 degrees. You can measure the temperature of ice water to show the freezing point. The boiling point is found by heating the water and taking the temperature of water when it starts to bubble vigorously.
We are aware that the temperature, the lower the air pressure as molecules move farther apart leaving more room between them. At the same time, we must realize that because there is more room between the molecules of air, more water vapor can enter the air. The demonstration I like to use to show that there are spaces between the molecules is to mix equal amounts of water and ditto fund. I place 50 ml of water in one graduated cylinder and 50 ml of ditto fluid in another cylinder. I then ask the class what will happen if I mix the two together. They are very surprised when the combined volume does not equal 100 ml. This demonstration illustrates to them that there are spaces between molecules and not all molecules are the same size.
Construction of a thermometer can be done by using an Erlenmeyer flask, 30 cm length of glass tubing, one hole rubber stopper and colored water. Insert the glass tube into the one hole stopper. Put a plug of colored water, about one inch, into the tube and have it at rest about half way up the tube. Place the stopper and tube into the flask and allow it to stabilize. Place a string at the upper level of the plug of water and then appear to squeeze the flask. Ask the students why the plug moved up the tube. Do not answer the question. Use something that will insulate the heat from your hands against the flask- and repeat the “squeezing” of the flask. Ask the students why the plug did not move this time. Ask and perform any other reasonable investigation they might want to perform with the apparatus. Finally decide what practical use this apparatus could be used for. (thermometer)
.Another type of thermometer that could be constructed is by using a 250 ml flask, a 125 ml flask, 2 rubber stoppers, a 30cm glass tube, and colored water. Fill the flask with colored water. Place the glass tube into the one hole stopper and gently put the stopper into the flask. Water will rise up into the glass tube. Gently heat the top portion of the tube to lower the air pressure. Now place the 125 ml flask and stopper onto the glass tubing. This is your expansion chamber. Heat the water very slowly and observe the water level. Do not overheat.
These two types of student and/or teacher constructed thermometers make the student understand the principle of how a thermometer operates and clarifies the definition of temperature.
To find the temperature on a weather map, you look in the upper left of the station model.
Dew point
The dew point is the point at which water vapor in the air will condense at that temperature and pressure. If the temperature is above freezing, dew forms on the ground when the air that comes in contact with the ground cools to that temperature. If the temperature is below freezing, frost forms.
The simplest way to find the dew point in the classroom is to use a thermometer, ice, water and a container that will allow moisture to form on the outside. Place the ice and thermometer into the container of water and stir gently. When moisture begins to form on the outside of the container, read and record the temperature. This is the dew point.
Precipitation
Precipitation is moisture that falls to earth from the sky. It is classified as rain, snow, sleet and hail. Precipitation starts as snow high up in the atmosphere. The temperature of the atmosphere will determine whether it will remain as snow or change to another form as it travels to earth.
The rain gauge is the instrument used to measure the amount of precipitation. I have found that it is best to purchase this instrument as precipitation generally does not come in large quantities.
Inches of precipitation over the last 3 hours are located m the lower left of the station model.
Relative Humidity
Although the relative humidity is not found on a station model it is a basic weather element.
Relative humidity refers to the amount of water vapor in the air compared to the amount that it can hold at that temperature and pressure.
Changes m temperature result in changes in relative humidity.
One way to measure relative humidity is to use a sling psychrometer. This device uses a wet bulb and a dry bulb thermometer. You swing these instruments around until the temperature does not go any lower. You then use a chart that will allow you to find the relative humidity. You can construct a sling psychrometer by connecting two plastic backed thermometers with double backed foam tape. For best results, have the bulb of the thermometer you will use for the wet bulb open to the air. This will allow for a better air flow for evaporation to occur when the wet gauze is applied to the thermometer.
You can also construct a hygrometer to measure relative humidity. You still use a wet bulb and dry bulb thermometer but you fan the thermometers instead of spinning them around. The same chart is still used to find the relative humidity.
Weather Map
These weather elements are taken at specific times each day and the readings sent to the National Weather Bureau. The information then is used to construct a weather map. Plotting this information on a map allows the meteorologist to make weather predictions for the coming days.
The map shows the location of high and low pressure regions, types of fronts, and the basic weather elements.
Collect the daily weather map from the local paper and place it in your bulletin board. Have the students trace the weather patterns for about two weeks. After the first week, have the students try to guess what the weather will be like at various places in the United States the next day by looking at the weather map.
