Monitoring the Earth's Atmosphere

Teacher's Notes

Setting up a weather station on Mars Transparency Master

The weather on all the terrestrial planets (Venus, Earth and Mars) is governed by the same principles. In general, energy from the Sun heats the planet's surface and its atmosphere. This energy is transported over the planet's surface by convection and currents in both the atmosphere and oceans. The Earth's oceans are a major factor in controlling the Earth's climate and weather.

Things to emphasize

1. All weather events, on all scales, are driven by energy from the Sun.
2. Heating of the atmosphere causes pressure variations to form.
3. Pressure differences cause the air to flow from regions of high pressure to regions of lower pressure. This air motion we call "wind".
4. Planetary rotation plays an important role in the behaviour of a planet's atmosphere.
5. All agriculture (and hence human survival) is dependant upon the weather.
6. On Mars, as on Earth, the atmosphere behaves according to well understood (but difficult to predict) mechanisms
7. Seasons cannot be accurately predicted from the weather, therefore seasons are calendar events created by astronomers.
8. Climate is the "average" weather of a location, averaged over twenty five years or more.
9. Extremely general weather predictions based on seasons, can be predicted with 100% accuracy. ( e.g. The first day of summer begins at 4:32am EDT Tuesday June 21st, and it will be warmer than winter)
10. Generalized weather predictions based on climate, can be predicted with 90-99% accuracy( e.g. In July, Arizona will be hot and dry)
11. Detailed daily weather predictions based on daily observations of barometric pressure and wind conditions, can be predicted with varying (depending upon whom you ask!) accuracy.
12. Science investigation involves a multi-step inquiry process: ask an initial question, plan the investigation, record observations and collect data, analyse data to draw a conclusion, and communicate the findings.

Build Some Instruments

Build A Hydrometer

Use a pin or a tack to fasten a humidity pointer onto a piece of cardboard, labelled as indicated in the figure shown below. Tie one end of a strong human hair to the humidity pointer, and the other end of the hair to the top of the cardboard. Treat the pointer as a third class lever. The closer the hair is tied to the fulcrum, the more movement you will observe in the pointer as the humidity changes. Although the dimensions of the hydrometer are not critical, the longer the hair, the better.

Transparency Master

Explanation A human hair is sensitive to the amount of water vapour in the air. As the air becomes more humid, the natural elasticity in the hair "relaxes" and the hair gets longer. Conversely, a dry hair contracts and becomes shorter. We make use of this property of hair to build the classroom hygrometer shown in the figure to the left. This device is for indoor use only.

Transparency Master

A Classroom Barometer A two litre juice can with the lid cut off makes a good barometer. A cut latex balloon, held in place with an elastic band, is used to seal the air in the container. The "pointer" is made of two drinking straws taped to the centre of the balloon, and resting on the lip of the juice can as shown. Slit one end about 1-2cm and insert the end of one straw inside the other before taping them together. Fold a piece of sturdy paper in half and mark it in easily readable increments. Place the paper beside the barometer so that the pointer extends over to the paper, but does not touch it. NOTE: This device is also sensitive to changes in temperature as well as pressure, therefore it is recommenced that the barometer should be placed in a location where there temperature is likely to remain fairly constant.

Monitor the Atmosphere

Activities

1. Plot a daily record of the barometric pressure taking observations twice a day for at least one month. Record with each reading the current weather conditions.
   
   
2. Calibrate the classroom barometer in kilopascals using the barometric pressure from local radio or TV weathercasts.
   
   
3. Investigate how "air masses" are related to high and low pressure cells.
   
   
4. Monitor the humidity in your classroom. Is there any relationship between the daily weather, the seasonal weather and the humidity of the air in the classroom? Can you explain any patterns you find?
   
   
5. Weather vocabulary, Student Activity Master
   
   
6. How cold is it?, Student Activity Master

Pressure "waves"

Air flows from regions of high pressure to regions of lower pressure. The creates a phenomena we call the wind. A large pressure difference between to two points causes the wind to blow more strongly than when the pressure difference between those two points is less.

On the surface of the Earth we live at the bottom of an ocean of air. And just like any ocean, the ocean of air has waves rolling along the top. Of course, unlike the surface of the ocean, the atmosphere has no sharply defined "edge" or "top", but it still has waves on it nonetheless. For example, we could define the "top" as the layer above the Earth's surface where the atmospheric pressure is exactly 2 kilopascals (2kPa).

Transparency Master

As the waves pass overhead we can observe their passage as changes in barometric pressure on the Earth's surface.

It is the passage of these waves that is responsible for the changes in weather that we experience each day.

Transparency Master	Under a low pressure the weather is stormy (Winnipeg), under a high pressure the weather is fair (Calgary). When the barometer is "falling", (changing), and pressure is becoming lower (Thunder Bay) the weather will get worse within the next 12 hours. When the barometer is "rising ", (the pressure is becoming higher) (Regina) the weather will get much better within the next 12 hours.

By carefully monitoring changes in a barometer one can make 12h weather forecasts which are about 90% accurate in terms of general weather conditions.

Topics for class discussion

1. It has been stated that "without astronomy there can be no civilization."

   The reasoning behind this statement is basically this:

   • The first step beyond the nomadic, hunter-gatherer society requires organized agriculture.
   • Organized agriculture requires a knowledge of when to plough fields and sow crop seeds.
   • Weather is far too variable to predict accurately the true beginning of Spring (or related events such as the flooding of the Nile in ancient Egypt) For example, if one were to plant a crop too early it may be killed by frost or washed away by floods. Planting a crop too late in the year may not allow it to mature or ripen.
   • Astronomical events are required to know exactly when the seasons are changing and therefore when to plant crops.

   In light of the above, discuss the variability of the weather with respect to the seasons with your students.

2. The Martian year is approximately twice as long as the Earth year. How long (compared to the Earth) would you expect each season to last on Mars?

3. What features of Mars might make its weather systems somewhat easier to predict than weather systems on Earth?

   ---

   [Home]

   Prepared by YES I Can! Science
   Faculty of Pure and Applied Science, York University