Background for Teachers
Where's Weather Made?
Even though we noted on the Student Research Page that all weather gets created in the troposphere, technically, almost all weather gets created there. The other layers of the atmosphere do have a little bit of influence over weather-making.
The troposphere is its thinnest at the poles, where it measures about 5 miles. At the equator it's the thickest, at approximately 11 miles.
Even though it's just one of the five layers, the troposphere accounts for a whopping half of our planet's atmosphere.
Here are the five layers of Earth's atmosphere, from the closest to us to farthest from us:
1. Troposphere – Where almost all weather is made. About 5-11 miles above us.
2. Stratosphere – Where you'll find ozone and where meteorologists send weather balloons. About 31 miles above us.
3. Mesosphere – Meteorites usually hit this layer and that's where they are when we spot them. About 53 miles above us.
4. Thermosphere – Strangely, even though large doses of ultraviolent and x-ray radiation from the sun create high temperatures here (up to 3600° F!), life in the thermosphere would feel really cold to us because, with the ultra thin air, there just aren't enough molecules to heat up our skin. About 430 miles above us.
5. Exosphere – Remember what the prefix "exo" means? "Outer." Makes sense, considering that this is the outer most layer of our atmosphere. Here atoms and molecules escape into space. This is also where we send satellites to orbit. About 6,200 miles above us.
The National Earth Science Teachers' Association (NESTA) offers "Windows to the Universe – Atmosphere" if you're hungry for more technical information on this topic. http://www.windows2universe.org/earth/Atmosphere/layers_activity_print.html.
What Makes Weather?
On the Student Resource Page we say that four elements work together to make weather:
- air pressure
While, we have simplified the list for the sake of 4th-graders, these certainly do create the basic ingredients for weather-making.
Air pressure plays a central role in weather-making. As atoms and molecules that live within the atmosphere move around randomly, they exert pressure when they bump into one another.
Their movements can be in all directions. Atoms and molecules can come from the bottom, the top, sides, diagonally, etc. This is important for your students to understand.
As a general rule, when elevation increases the number of molecules decreases. Thus, the density of the air also decreases. Less dense air means less air pressure.
Air temperature also effects density, thus, air pressure. Here’s how: Warm air is less dense than cold air because the warmer molecules are the faster they move. The faster they move the farther apart they are from one another. The farther apart they are from one another, the less dense the air is.
On the Student Research Page we discuss “high” and “low” pressure. We write:
Air moves from places where it’s being pushed on hard, to places where it’s not being pushed on as hard. In official weather words we say that the air moves from places of "high pressure" to places of "low pressure."
This simplifies the concept of "more density," which is "high pressure," and "low density," which is "low pressure" for the children.
- Cold air has more density; therefore, more air pressure, than warm air.
- Warm air has less density; therefore, less air pressure than cold air.
- High pressure is caused by: Low elevation and/or cold air
- Low pressure is caused by: High elevation and/or warm air
PLEASE NOTE!! This is VERY simplified! Air pressure is an extremely complex topic.
Precipitation is part of the hydrologic cycle. Recall that the prefix "hydro" means "water" and it comes as no surprise that the hydrologic cycle is simply the formal term for the "water cycle." This refers to the continuous movement of water on, above, and below Earth’s surface. Through the hydrologic cycle water transforms itself through all three stages of matter: solid, liquid, and gas.
The U.S. Geological Survey has excellent resources on the water cycle. http://ga.water.usgs.gov/edu/watercycleprecipitation.html
According to The Royal Meteorological Society (which has been around since 1850!), only 0.034% of Earth's water is in the atmosphere at any one time, while about 97% of it is in our oceans. Be sure to print out this great PDF they've created especially for teachers: http://www.rmets.org/pdf/science_weather/precipitation.pdf
Since precipitation falls from clouds, you want might to direct your students to http://eo.ucar.edu/webweather/cloudhome.html where they can learn all about these puffy players in the weather-making game.
The atoms and molecules that create changes in air pressure usually get set into motion by changes in temperature.
REMEMBER - Air temperature effects density, thus, air pressure. Here’s how: Warm air is less dense than cold air because the warmer molecules are the faster they move. The faster they move the farther apart they are from one another. The farther apart they are from one another, the less dense the air is.
So, cold air has more density and more air pressure than warm air. And warm air has less density and less air pressure than cold air.
CLIMATE describes patterns of weather over a long time.
WEATHER describes what’s happening right now or what will happen tomorrow.