Martian Dust Storms

Teacher's Notes

Things to emphasize

1. All weather events, on all scales, are driven by energy from the Sun.
2. All weather events occur in a layer of the atmosphere called the troposphere.
3. All agriculture (and hence human survival) is dependant upon the weather.
4. Without some method of distributing the Sun's energy over the Earth's surface, it would be uninhabitable, i.e. The equatorial regions would exceed the boiling point of water and the poles would be cold enough the liquify the atmosphere.
5. A moderate greenhouse effect and atmospheric convection are responsible for making the Earth's atmosphere habitable.
6. 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 and Atmospheric Convection Simulator

The objective of this project is to demonstrate auto-convection and to emphasize that this is the primary method of both local and global heat transfer.

Transparency Master Transparency Master

General Instructions You may choose to build either a Mars-scape or a seascape to demonstrate the principles of convection. The basic design requires that one build a small stage, such as one might build for a puppet show. The key feature of this set is that it is in an airtight cardboard box, except for the two tin-can chimneys. Clear food wrap (or heat shrink window covering) provides an air tight cover over the front. The chimneys are made from discarded tin cans (both ends removed). A small 2-3cm lip along the bottom will hid any items on the "floor" of the box and a flap on one side should be provided to allow easy access to the interior without disturbing the clear plastic across the front.

Transparency Master (Seaside) Transparency Master (Mars)

Construction Details Students can create their own backdrop, however the scene must be a "shore scape" with the beach on the left and the ocean on the right. A "hot pad" (the kind that is heated by placing it in boiling water) is placed under the left hand chimney. Use oven mitts and tongs to handle hot objects. After a few minutes the system will begin to auto-convect. The air flow can be traced using a glowing stick of "punk" or incense.

Activities

Set up your Martian (or Seaside) convection simulator and trace the air currents through it.

The Sun heats the surface of Mars during the Martian daytime. Dark areas absorb more sunlight than bright areas of the Martian surface. Dark regions absorb sunlight, bright regions reflect sunlight. This causes the dark areas to become warmer than the brighter areas of the planet's surface. This effect triggers convection in the Martian atmosphere. This effect can be demonstrated nicely with the convection simulator.

On Earth, convection is the single most important factor driving all the winds on all scales, from little breezes to trade winds and hurricanes.

Although the sun is the primary source of heat, strong convection winds can be caused by warm water. This is especially true of hurricanes. Hurricanes are huge storms driven by the energy given off by warm ocean waters.

Hurricanes get additional energy from the condensation of water vapour as clouds form. In other words, hurricanes are fuelled by water vapour.

Once hurricanes reach land, and the source of water vapour is removed, they quickly weaken and decay into much less violent storms and eventually dissipate.

Topics for class discussion

Based on your observations, and your understanding of convection, answer the following:

1. In the afternoon, where would you expect clouds to form; over the ocean or over the land? Go to the library and find satellite images to support or refute your conclusions.

2. In a convectional storm, where would you expect the barometric pressure to be highest, and where would you expect it to be lowest?

3. How does your response to the questions above relate to your knowledge of high and low pressure systems?

4. On Mars, atmospheric dust absorbs sunlight very efficiently. Once convection triggers a small dust storm the atmosphere containing the dust absorbs even more sunlight. What effect does this create with respect to the size of a Martian dust storm?