Raymond W. Brooks
Weather is generally defined as the condition of the atmosphere at a particular time and a particular place. The main factors for these conditions are the amount and angle of the sunlight that reach the earth. These factors cause a global wind pattern. At the equator we have what are called the Trade Winds. These exist between 0° and 30° north and south of the equator. At 30° to 60° north or south of the equator we have the Prevailing Westerlies and the final loops are called the Polar Easterlies that are located from 60° to 90° north or south of the equator.
One of the most important effects of the Sun on the Earth is the water cycle. This cycle constantly moves water from the atmosphere to earth and back into the atmosphere making it a renewable resource. If we did not have this cycle, we would not have life, as we know it. We should review or introduce the water cycle at this time. Remember a cycle is something that keeps happening over and over, so it really does not matter where you start. Basically the cycle is precipitation, run-off, evaporation, and condensation. A good website for this explanation with a great diagram is:
http://ga.water.usgs.gov/edu/watercycle.html
When we talk about weather, the condition of the atmosphere, we generally concern ourselves with seven basic weather elements. We now will spend some time on how to measure these basic weather elements and see their importance in a weather forecast. If weather is a class project, you may divide the class into groups with each investigating one basic weather element and constructing an instrument to measure that element. The construction of the instrument(s) helps them to understand the basic principle of the measuring device we use to measure that element.
These elements are:
Precipitation
: Moisture that falls to the earth in the form of rain, snow, sleet or hail.
The form of precipitation that eventually falls to earth depends on the temperature of the atmospheric layers as it travels to earth. All precipitation begins as snow.
There are different ways to construct a precipitation gauge. You can go online to find one that you prefer to construct.
One online source is: http://www.miamisci.org/hurricane/moisture.html
Air Pressure
: The pressure of the atmosphere on people and objects at the surface of the earth.
The barometer is the instrument we use to measure air pressure. Normal air pressure is 14.7 psi (pounds per square inch.) This means that on every square inch our body, a pressure of 14.7 psi is acting on it. A change in air pressure is an indicator of a change in weather. If the air pressure rises, it generally means good weather. If the air pressure falls, poor weather conditions can be expected.
When the air descends, it becomes warmer making the spaces between the molecules greater and room for more water vapor molecules. This downward movement also increases the pressure on the earth's surface causing an increase in air pressure readings.
Just the opposite occurs when the air ascends. The air becomes cooler causing the molecules to come closer together that force water vapor molecules to combine. When they combine, clouds form and precipitation may fall. The upward movement takes pressure off the earth's surface and the barometer readings fall.
Again, you can go online and find a way to construct a barometer of your choice.
One source is: http://www.miamisci.org/hurrican/airpressure.html
Air Temperature
: Molecular activity of air molecules.
Air temperature is an important element. It determines when crops will grow, what crops will grow, what we will wear and what activities we can perform on a particular day.
We read a thermometer by the rising and falling of a liquid in a tube that air has been removed. This vacuum allows the liquid to move up and down without resistance. As stated earlier, temperature is the measure of molecular activity. The warmer the liquid, the greater the molecular motion and expansion occurs. Just the opposite occurs with the cooling of the liquid.
A good way to show what happens in a thermometer is to build a water thermometer. If you have access to an Interaction of Earth and Time textbook, there is a good demonstration activity showing the principle of the thermometer.
You should make sure your students have knowledge of the Celsius and Fahrenheit scales. A good website is: http://miamisci.org/hurricane/temperature.html
Relative Humidity
: Amount of moisture in the air compared to what it can hold at
that temperature and pressure.
We are most comfortable when the relative humidity is about 45%. As the temperature changes, so can the relative humidity. The warmer the air, the more spaces between air molecules for water vapor. The cooler the air, the less space for water vapor. When we reach a relative humidity of 100%, we will have some type of precipitation.
We can use an instrument called a sling psychrometer to measure relative humidity.
Again you can find how to construct this instrument in a textbook or online.
One online source is: http://www.miamisci.org/hurricane/moisture.html
Wind
(Speed & Direction): Horizontal movement of air.
Wind is caused by the difference in pressure. The greater the pressure difference, the stronger the wind. The direction the wind is coming from is how it is named.
Wind direction is measured by a wind vane and wind speed by an anemometer. There are different ways to construct and calibrate these instruments. The type you choose will depend on the grade level of your students.
One website is: http://www.miamisci.org/hurricane/wind.html
Clouds
: Formed when moisture in the air condenses around solid particles in the atmosphere. There are four basic cloud types with a Latin root. Cummulus (heap), stratus(layer), cirrus(curl) and nimbus(rain).
Clouds are classified as high-level, mid-level, low-level and clouds with vertical development. To go into greater detail with clouds, go to the website: http://ww2010.atmos.uiuc.edu/(GH)/guides/mtr/cld/cldtyp/home.rxml
If you would like to make a cloud in the classroom, go to website: http://www.ucar.edu/educ_outreach/webweather/cloudact2.html
"Create a Portable Cloud"
Dew Point
: The temperature at which air is saturated and condenses to a liquid.
A good way to start their understanding of dew point is to ask students what happen on the outside of a cold can of soda when you take it out of the refrigerator in the summer. Most will say moisture appears on the out side. Ask them if they know why this happens. Most probably will not know. You can explain to them that the air is cooled when it touches the can causing the water vapor molecules to come closer together and condense on the outside of the can. Tell them the same thing happens in the atmosphere when the air is cooled to the dew point.
One way for them to find dew point is to fill a glass ¾ full of water. Add ice to the water and stir carefully with a thermometer. Take the thermometer reading when moisture begins to form on the container. This is the dew point.
Weather Station Model
If you would like your students to be able to plot and read information on a weather station model, go to: http://cimss.ssec.wisc.edu/wxwise/station/page2.html
